x86/ftrace: enable EXECMEM_ROX_CACHE for ftrace allocations
For the most part ftrace uses text poking and can handle ROX memory. The
only place that requires writable memory is create_trampoline() that
updates the allocated memory and in the end makes it ROX.
Use execmem_alloc_rw() in x86::ftrace::alloc_tramp() and enable ROX cache
for EXECMEM_FTRACE when configuration and CPU features allow that.
Link: https://lkml.kernel.org/r/20250713071730.4117334-9-rppt@kernel.org Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Steven Rostedt (Google) <rostedt@goodmis.org> Cc: Daniel Gomez <da.gomez@samsung.com> Cc: Masami Hiramatsu (Google) <mhiramat@kernel.org> Cc: Petr Pavlu <petr.pavlu@suse.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Instead of overriding this method, add EXECMEM_KPROBES entry in
execmem_info with pgprot set to PAGE_KERNEL_ROX and use ROX cache when
configuration and CPU features allow it.
Link: https://lkml.kernel.org/r/20250713071730.4117334-8-rppt@kernel.org Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org> Cc: Daniel Gomez <da.gomez@samsung.com> Cc: Petr Pavlu <petr.pavlu@suse.com> Cc: Steven Rostedt (Google) <rostedt@goodmis.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
execmem: drop writable parameter from execmem_fill_trapping_insns()
After update of execmem_cache_free() that made memory writable before
updating it, there is no need to update read only memory, so the writable
parameter to execmem_fill_trapping_insns() is not needed. Drop it.
Link: https://lkml.kernel.org/r/20250713071730.4117334-7-rppt@kernel.org Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Daniel Gomez <da.gomez@samsung.com> Cc: Masami Hiramatsu (Google) <mhiramat@kernel.org> Cc: Petr Pavlu <petr.pavlu@suse.com> Cc: Steven Rostedt (Google) <rostedt@goodmis.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
execmem: add fallback for failures in vmalloc(VM_ALLOW_HUGE_VMAP)
When execmem populates ROX cache it uses vmalloc(VM_ALLOW_HUGE_VMAP).
Although vmalloc falls back to allocating base pages if high order
allocation fails, it may happen that it still cannot allocate enough
memory.
Right now ROX cache is only used by modules and in majority of cases the
allocations happen at boot time when there's plenty of free memory, but
upcoming enabling ROX cache for ftrace and kprobes would mean that execmem
allocations can happen when the system is under memory pressure and a
failure to allocate large page worth of memory becomes more likely.
Fallback to regular vmalloc() if vmalloc(VM_ALLOW_HUGE_VMAP) fails.
Link: https://lkml.kernel.org/r/20250713071730.4117334-6-rppt@kernel.org Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Daniel Gomez <da.gomez@samsung.com> Cc: Masami Hiramatsu (Google) <mhiramat@kernel.org> Cc: Petr Pavlu <petr.pavlu@suse.com> Cc: Steven Rostedt (Google) <rostedt@goodmis.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Currently execmem_cache_free() ignores potential allocation failures that
may happen in execmem_cache_add(). Besides, it uses text poking to fill
the memory with trapping instructions before returning it to cache
although it would be more efficient to make that memory writable, update
it using memcpy and then restore ROX protection.
Rework execmem_cache_free() so that in case of an error it will defer
freeing of the memory to a delayed work.
With this the happy fast path will now change permissions to RW, fill the
memory with trapping instructions using memcpy, restore ROX permissions,
add the memory back to the free cache and clear the relevant entry in
busy_areas.
If any step in the fast path fails, the entry in busy_areas will be marked
as pending_free. These entries will be handled by a delayed work and
freed asynchronously.
To make the fast path faster, use __GFP_NORETRY for memory allocations and
let asynchronous handler try harder with GFP_KERNEL.
Link: https://lkml.kernel.org/r/20250713071730.4117334-4-rppt@kernel.org Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Daniel Gomez <da.gomez@samsung.com> Cc: Masami Hiramatsu (Google) <mhiramat@kernel.org> Cc: Petr Pavlu <petr.pavlu@suse.com> Cc: Steven Rostedt (Google) <rostedt@goodmis.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Some callers of execmem_alloc() require the memory to be temporarily
writable even when it is allocated from ROX cache. These callers use
execemem_make_temp_rw() right after the call to execmem_alloc().
Wrap this sequence in execmem_alloc_rw() API.
Link: https://lkml.kernel.org/r/20250713071730.4117334-3-rppt@kernel.org Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org> Reviewed-by: Daniel Gomez <da.gomez@samsung.com> Reviewed-by: Petr Pavlu <petr.pavlu@suse.com> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Masami Hiramatsu (Google) <mhiramat@kernel.org> Cc: Steven Rostedt (Google) <rostedt@goodmis.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Patch series "x86: enable EXECMEM_ROX_CACHE for ftrace and kprobes", v3.
These patches enable use of EXECMEM_ROX_CACHE for ftrace and kprobes
allocations on x86.
They also include some ground work in execmem.
Since the execmem model for caching large ROX pages changed from the
initial assumption that the memory that is allocated from ROX cache is
always ROX to the current state where memory can be temporarily made RW
and then restored to ROX, we can stop using text poking to update it.
This also saves the hassle of trying lock text_mutex in
execmem_cache_free() when kprobes already hold that mutex.
This patch (of 8):
The execmem_update_copy() that used text poking was required when memory
allocated from ROX cache was always read-only. Since now its permissions
can be switched to read-write there is no need in a function that updates
memory with text poking.
mm: fix a UAF when vma->mm is freed after vma->vm_refcnt got dropped
By inducing delays in the right places, Jann Horn created a reproducer for
a hard to hit UAF issue that became possible after VMAs were allowed to be
recycled by adding SLAB_TYPESAFE_BY_RCU to their cache.
Race description is borrowed from Jann's discovery report:
lock_vma_under_rcu() looks up a VMA locklessly with mas_walk() under
rcu_read_lock(). At that point, the VMA may be concurrently freed, and it
can be recycled by another process. vma_start_read() then increments the
vma->vm_refcnt (if it is in an acceptable range), and if this succeeds,
vma_start_read() can return a recycled VMA.
In this scenario where the VMA has been recycled, lock_vma_under_rcu()
will then detect the mismatching ->vm_mm pointer and drop the VMA through
vma_end_read(), which calls vma_refcount_put(). vma_refcount_put() drops
the refcount and then calls rcuwait_wake_up() using a copy of vma->vm_mm.
This is wrong: It implicitly assumes that the caller is keeping the VMA's
mm alive, but in this scenario the caller has no relation to the VMA's mm,
so the rcuwait_wake_up() can cause UAF.
The diagram depicting the race:
T1 T2 T3
== == ==
lock_vma_under_rcu
mas_walk
<VMA gets removed from mm>
mmap
<the same VMA is reallocated>
vma_start_read
__refcount_inc_not_zero_limited_acquire
munmap
__vma_enter_locked
refcount_add_not_zero
vma_end_read
vma_refcount_put
__refcount_dec_and_test
rcuwait_wait_event
<finish operation>
rcuwait_wake_up [UAF]
Note that rcuwait_wait_event() in T3 does not block because refcount was
already dropped by T1. At this point T3 can exit and free the mm causing
UAF in T1.
To avoid this we move vma->vm_mm verification into vma_start_read() and
grab vma->vm_mm to stabilize it before vma_refcount_put() operation.
If an anon folio is mapped into userspace, its anon_vma must be alive,
otherwise rmap walks can hit UAF.
There have been syzkaller reports a few months ago[1][2] of UAF in rmap
walks that seems to indicate that there can be pages with elevated
mapcount whose anon_vma has already been freed, but I think we never
figured out what the cause is; and syzkaller only hit these UAFs when
memory pressure randomly caused reclaim to rmap-walk the affected pages,
so it of course didn't manage to create a reproducer.
Add a VM_WARN_ON_FOLIO() when we add/remove mappings of anonymous folios
to hopefully catch such issues more reliably.
Lorenzo Stoakes [Fri, 25 Jul 2025 14:29:01 +0000 (15:29 +0100)]
mm: remove mm/io-mapping.c
This is dead code, which was used from commit b739f125e4eb ("i915: use
io_mapping_map_user") but reverted a month later by commit 0e4fe0c9f2f9
("Revert "i915: use io_mapping_map_user"") back in 2021.
Since then nobody has used it, so remove it.
[akpm@linux-foundation.org: update Documentation/core-api/mm-api.rst, per Vlastimil] Link: https://lkml.kernel.org/r/20250725142901.81502-1-lorenzo.stoakes@oracle.com Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Acked-by: David Hildenbrand <david@redhat.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> Cc: Liam Howlett <liam.howlett@oracle.com> Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Rapoport <rppt@kernel.org> Cc: Suren Baghdasaryan <surenb@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Dev Jain [Thu, 24 Jul 2025 05:23:01 +0000 (10:53 +0530)]
khugepaged: optimize collapse_pte_mapped_thp() by PTE batching
Use PTE batching to batch process PTEs mapping the same large folio. An
improvement is expected due to batching mapcount manipulation on the
folios, and for arm64 which supports contig mappings, the number of
TLB flushes is also reduced.
Note that we do not need to make a change to the check
"if (folio_page(folio, i) != page)"; if i'th page of the folio is equal
to the first page of our batch, then i + 1, .... i + nr_batch_ptes - 1
pages of the folio will be equal to the corresponding pages of our
batch mapping consecutive pages.
Link: https://lkml.kernel.org/r/20250724052301.23844-4-dev.jain@arm.com Signed-off-by: Dev Jain <dev.jain@arm.com> Acked-by: David Hildenbrand <david@redhat.com> Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Reviewed-by: Zi Yan <ziy@nvidia.com> Cc: Barry Song <baohua@kernel.org> Cc: Liam Howlett <liam.howlett@oracle.com> Cc: Mariano Pache <npache@redhat.com> Cc: Ryan Roberts <ryan.roberts@arm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Dev Jain [Thu, 24 Jul 2025 05:23:00 +0000 (10:53 +0530)]
khugepaged: optimize __collapse_huge_page_copy_succeeded() by PTE batching
Use PTE batching to batch process PTEs mapping the same large folio. An
improvement is expected due to batching refcount-mapcount manipulation on
the folios, and for arm64 which supports contig mappings, the number of
TLB flushes is also reduced.
Link: https://lkml.kernel.org/r/20250724052301.23844-3-dev.jain@arm.com Signed-off-by: Dev Jain <dev.jain@arm.com> Acked-by: David Hildenbrand <david@redhat.com> Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Cc: Barry Song <baohua@kernel.org> Cc: Liam Howlett <liam.howlett@oracle.com> Cc: Mariano Pache <npache@redhat.com> Cc: Ryan Roberts <ryan.roberts@arm.com> Cc: Zi Yan <ziy@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
If the underlying folio mapped by the ptes is large, we can process those
ptes in a batch using folio_pte_batch().
For arm64 specifically, this results in a 16x reduction in the number of
ptep_get() calls, since on a contig block, ptep_get() on arm64 will
iterate through all 16 entries to collect a/d bits. Next, ptep_clear()
will cause a TLBI for every contig block in the range via
contpte_try_unfold(). Instead, use clear_ptes() to only do the TLBI at
the first and last contig block of the range.
For split folios, there will be no pte batching; the batch size returned
by folio_pte_batch() will be 1. For pagetable split folios, the ptes will
still point to the same large folio; for arm64, this results in the
optimization described above, and for other arches, a minor improvement is
expected due to a reduction in the number of function calls and batching
atomic operations.
This patch (of 3):
Let's add variants to be used where "full" does not apply -- which will
be the majority of cases in the future. "full" really only applies if
we are about to tear down a full MM.
Use get_and_clear_ptes() in existing code, clear_ptes() users will
be added next.
Link: https://lkml.kernel.org/r/20250724052301.23844-2-dev.jain@arm.com Signed-off-by: David Hildenbrand <david@redhat.com> Signed-off-by: Dev Jain <dev.jain@arm.com> Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com> Reviewed-by: Barry Song <baohua@kernel.org> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Reviewed-by: Zi Yan <ziy@nvidia.com> Cc: Liam Howlett <liam.howlett@oracle.com> Cc: Mariano Pache <npache@redhat.com> Cc: Ryan Roberts <ryan.roberts@arm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Lorenzo Stoakes [Fri, 25 Jul 2025 08:29:45 +0000 (09:29 +0100)]
mm/mseal: rework mseal apply logic
The logic can be simplified - firstly by renaming the inconsistently named
apply_mm_seal() to mseal_apply().
We then wrap mseal_fixup() into the main loop as the logic is simple
enough to not require it, equally it isn't a hugely pleasant pattern in
mprotect() etc. so it's not something we want to perpetuate.
We eliminate the need for invoking vma_iter_end() on each loop by directly
determining if the VMA was merged - the only thing we need concern
ourselves with is whether the start/end of the (gapless) range are offset
into VMAs.
This refactoring also avoids the rather horrid 'pass pointer to prev
around' pattern used in mprotect() et al.
No functional change intended.
Link: https://lkml.kernel.org/r/ddfa4376ce29f19a589d7dc8c92cb7d4f7605a4c.1753431105.git.lorenzo.stoakes@oracle.com Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Reviewed-by: Pedro Falcato <pfalcato@suse.de> Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com> Acked-by: David Hildenbrand <david@redhat.com> Acked-by: Jeff Xu <jeffxu@chromium.org> Cc: Jann Horn <jannh@google.com> Cc: Kees Cook <kees@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Lorenzo Stoakes [Fri, 25 Jul 2025 08:29:44 +0000 (09:29 +0100)]
mm/mseal: simplify and rename VMA gap check
The check_mm_seal() function is doing something general - checking whether
a range contains only VMAs (or rather that it does NOT contain any
unmapped regions).
So rename this function to range_contains_unmapped().
Additionally simplify the logic, we are simply checking whether the last
vma->vm_end has either a VMA starting after it or ends before the end
parameter.
This check is rather dubious, so it is sensible to keep it local to
mm/mseal.c as at a later stage it may be removed, and we don't want any
other mm code to perform such a check.
Lorenzo Stoakes [Fri, 25 Jul 2025 08:29:43 +0000 (09:29 +0100)]
mm/mseal: small cleanups
Drop the wholly unnecessary set_vma_sealed() helper(), which is used only
once, and place VMA_ITERATOR() declarations in the correct place.
Retain vma_is_sealed(), and use it instead of the confusingly named
can_modify_vma(), so it's abundantly clear what's being tested, rather
then a nebulous sense of 'can the VMA be modified'.
No functional change intended.
Link: https://lkml.kernel.org/r/98cf28d04583d632a6eb698e9ad23733bb6af26b.1753431105.git.lorenzo.stoakes@oracle.com Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com> Reviewed-by: Pedro Falcato <pfalcato@suse.de> Acked-by: David Hildenbrand <david@redhat.com> Acked-by: Jeff Xu <jeffxu@chromium.org> Cc: Jann Horn <jannh@google.com> Cc: Kees Cook <kees@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Lorenzo Stoakes [Fri, 25 Jul 2025 08:29:42 +0000 (09:29 +0100)]
mm/mseal: update madvise() logic
The madvise() logic is inexplicably performed in mm/mseal.c - this ought
to be located in mm/madvise.c.
Additionally can_modify_vma_madv() is inconsistently named and, in
combination with is_ro_anon(), is very confusing logic.
Put a static function in mm/madvise.c instead - can_madvise_modify() -
that spells out exactly what's happening. Also explicitly check for an
anon VMA.
Also add commentary to explain what's going on.
Essentially - we disallow discarding of data in mseal()'d mappings in
instances where the user couldn't otherwise write to that data.
We retain the existing behaviour here regarding MAP_PRIVATE mappings of
file-backed mappings, which entails some complexity - while this, strictly
speaking - appears to violate mseal() semantics, it may interact badly
with users which expect to be able to madvise(MADV_DONTNEED) .text
mappings for instance.
We may revisit this at a later date.
No functional change intended.
Link: https://lkml.kernel.org/r/492a98d9189646e92c8f23f4cce41ed323fe01df.1753431105.git.lorenzo.stoakes@oracle.com Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com> Reviewed-by: Pedro Falcato <pfalcato@suse.de> Acked-by: David Hildenbrand <david@redhat.com> Cc: Jann Horn <jannh@google.com> Cc: Jeff Xu <jeffxu@chromium.org> Cc: Kees Cook <kees@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Lorenzo Stoakes [Fri, 25 Jul 2025 08:29:41 +0000 (09:29 +0100)]
mm/mseal: always define VM_SEALED
Patch series "mseal cleanups", v4.
Perform a number of cleanups to the mseal logic. Firstly, VM_SEALED is
treated differently from every other VMA flag, it really doesn't make
sense to do this, so we start by making this consistent with everything
else.
Next we place the madvise logic where it belongs - in mm/madvise.c. It
really makes no sense to abstract this elsewhere. In doing so, we go to
great lengths to explain very clearly the previously very confusing logic
as to what sealed mappings are impacted here.
In doing so, we retain existing logic regarding treatment of madvise()
discard operations for a sealed, read-only MAP_PRIVATE file-backed
mapping. This is something we likely need to revisit.
We then abstract out and explain the 'are there are any gaps in this range
in the mm?' check being performed as a prerequisite to mseal being
performed.
Finally, we simplify the actual mseal logic which is really quite
straightforward.
No functional change is intended.
This patch (of 4):
There is no reason to treat VM_SEALED in a special way, in each other case
in which a VMA flag is unavailable due to configuration, we simply assign
that flag to VM_NONE, so make VM_SEALED consistent with all other VMA
flags in this respect.
Additionally, use the next available bit for VM_SEALED, 42, rather than
arbitrarily putting it at 63 and update the declaration to match all other
VMA flags.
mm/damon/vaddr: skip isolating folios already in destination nid
damos_va_migrate_dests_add() determines the node a folio should be in
based on the struct damos_migrate_dests associated with the migration
scheme and adds the folio to the linked list corresponding to that node so
it can be migrated later. Currently, folios are isolated and added to the
list even if they are already in the node they should be in.
In using damon weighted interleave more, I've found that the overhead of
needlessly adding these folios to the migration lists can be quite high.
The overhead comes from isolating folios and placing them in the migration
lists inside of damos_va_migrate_dests_add(), as well as the cost of
handling those folios in damon_migrate_pages(). This patch eliminates
that overhead by simply avoiding the addition of folios that are already
in their intended location to the migration list.
To show the benefit of this patch, we start the test workload and start a
DAMON instance attached to that workload with a migrate_hot scheme that
has one dest field sending data to the local node. This way, we are only
measuring the overheads of the scheme, and not the cost of migrating
pages, since data will be allocated to the local node by default. I
tested with two workloads: the embedding reduction workload used in [1]
and a microbenchmark that allocates 20GB of data then sleeps, which is
similar to the memory usage of the embedding reduction workload.
The time taken in damos_va_migrate_dests_add() and damon_migrate_pages()
each aggregation interval is shown below.
Before this patch:
damos_va_migrate_dests_add damon_migrate_pages
microbenchmark ~2ms ~3ms
embedding reduction ~1s ~3s
After this patch:
damos_va_migrate_dests_add damon_migrate_pages
microbenchmark 0us ~40us
embedding reduction 0us ~100us
I did not do an in depth analysis for why things are much slower in the
embedding reduction workload than the microbenchmark. However, I assume
it's because the embedding reduction workload oversaturates the bandwidth
of the local memory node, increasing the memory access latency, and in
turn making the pointer chasing involved in iterating through a linked
list much slower. Regardless of that, this patch results in a significant
speedup.
Link: https://lkml.kernel.org/r/20250725163300.4602-1-bijan311@gmail.com Fixes: 19c1dc15c859 ("mm/damon/vaddr: use damos->migrate_dests in migrate_{hot,cold}") Signed-off-by: Bijan Tabatabai <bijantabatab@micron.com> Reviewed-by: SeongJae Park <sj@kernel.org> Reviewed-by: Raghavendra K T <raghavendra.kt@amd.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Suresh K C [Wed, 9 Jul 2025 17:46:57 +0000 (23:16 +0530)]
selftests: cachestat: add tests for mmap, refactor and enhance mmap test for cachestat validation
Add a cohesive test case that verifies cachestat behavior with
memory-mapped files using mmap(). Also refactor the test logic to reduce
redundancy, improve error reporting, and clarify failure messages for both
shmem and mmap file types.
[akpm@linux-foundation.org: coding-style cleanups] Link: https://lkml.kernel.org/r/20250709174657.6916-1-suresh.k.chandrappa@gmail.com Signed-off-by: Suresh K C <suresh.k.chandrappa@gmail.com> Reviewed-by: Joshua Hahn <joshua.hahnjy@gmail.com> Tested-by: Nhat Pham <nphamcs@gmail.com> Acked-by: Nhat Pham <nphamcs@gmail.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Shuah Khan <shuah@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Xuanye Liu [Wed, 23 Jul 2025 10:09:00 +0000 (18:09 +0800)]
mm: add process info to bad rss-counter warning
Enhance the debugging information in check_mm() by including the process
name and PID when reporting bad rss-counter states. This helps identify
which process is associated with the memory accounting issue.
Link: https://lkml.kernel.org/r/20250723100901.1909683-1-liuqiye2025@163.com Signed-off-by: Xuanye Liu <liuqiye2025@163.com> Acked-by: SeongJae Park <sj@kernel.org> Cc: Ben Segall <bsegall@google.com> Cc: David Hildenbrand <david@redhat.com> Cc: Dietmar Eggemann <dietmar.eggemann@arm.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: Juri Lelli <juri.lelli@redhat.com> Cc: Kees Cook <kees@kernel.org> Cc: Liam Howlett <liam.howlett@oracle.com> Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Cc: Mel Gorman <mgorman <mgorman@suse.de> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Rapoport <rppt@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Suren Baghdasaryan <surenb@google.com> Cc: Valentin Schneider <vschneid@redhat.com> Cc: Vincent Guittot <vincent.guittot@linaro.org> Cc: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
kasan: skip quarantine if object is still accessible under RCU
Currently, enabling KASAN masks bugs where a lockless lookup path gets a
pointer to a SLAB_TYPESAFE_BY_RCU object that might concurrently be
recycled and is insufficiently careful about handling recycled objects:
KASAN puts freed objects in SLAB_TYPESAFE_BY_RCU slabs onto its quarantine
queues, even when it can't actually detect UAF in these objects, and the
quarantine prevents fast recycling.
When I introduced CONFIG_SLUB_RCU_DEBUG, my intention was that enabling
CONFIG_SLUB_RCU_DEBUG should cause KASAN to mark such objects as freed
after an RCU grace period and put them on the quarantine, while disabling
CONFIG_SLUB_RCU_DEBUG should allow such objects to be reused immediately;
but that hasn't actually been working.
I discovered such a UAF bug involving SLAB_TYPESAFE_BY_RCU yesterday; I
could only trigger this bug in a KASAN build by disabling
CONFIG_SLUB_RCU_DEBUG and applying this patch.
Commit cd57b77197a4 ("ext4: Convert ext4_bio_write_page() to use a folio)
removed set_page_writeback_keepwrite() which was the last/only caller of
folio_start_writeback_keepwrite().
Link: https://lkml.kernel.org/r/20250722182230.2114587-1-joannelkoong@gmail.com Signed-off-by: Joanne Koong <joannelkoong@gmail.com> Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org> Reviewed-by: David Hildenbrand <david@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
wang lian [Mon, 21 Jul 2025 11:46:14 +0000 (19:46 +0800)]
selftests/mm: add process_madvise() tests
Add tests for process_madvise(), focusing on verifying behavior under
various conditions including valid usage and error cases.
[lianux.mm@gmail.com: v7] Link: https://lkml.kernel.org/r/20250729113109.12272-1-lianux.mm@gmail.com Link: https://lkml.kernel.org/r/20250729113109.12272-1-lianux.mm@gmail.com Link: https://lkml.kernel.org/r/20250721114614.40996-1-lianux.mm@gmail.com Signed-off-by: wang lian <lianux.mm@gmail.com> Suggested-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Suggested-by: David Hildenbrand <david@redhat.com> Suggested-by: Zi Yan <ziy@nvidia.com> Suggested-by: Mark Brown <broonie@kernel.org> Acked-by: SeongJae Park <sj@kernel.org> Reviewed-by: Zi Yan <ziy@nvidia.com> Tested-by: Zi Yan <ziy@nvidia.com> Cc: Christian Brauner <brauner@kernel.org> Cc: Jann Horn <jannh@google.com> Cc: Kairui Song <ryncsn@gmail.com> Cc: Liam Howlett <liam.howlett@oracle.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Baolin Wang [Thu, 31 Jul 2025 01:53:43 +0000 (09:53 +0800)]
mm: shmem: fix the shmem large folio allocation for the i915 driver
After commit acd7ccb284b8 ("mm: shmem: add large folio support for
tmpfs"), we extend the 'huge=' option to allow any sized large folios for
tmpfs, which means tmpfs will allow getting a highest order hint based on
the size of write() and fallocate() paths, and then will try each
allowable large order.
However, when the i915 driver allocates shmem memory, it doesn't provide
hint information about the size of the large folio to be allocated,
resulting in the inability to allocate PMD-sized shmem, which in turn
affects GPU performance.
Patryk added:
: In my tests, the performance drop ranges from a few percent up to 13%
: in Unigine Superposition under heavy memory usage on the CPU Core Ultra
: 155H with the Xe 128 EU GPU. Other users have reported performance
: impact up to 30% on certain workloads. Please find more in the
: regressions reports:
: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/14645
: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/13845
:
: I believe the change should be backported to all active kernel branches
: after version 6.12.
To fix this issue, we can use the inode's size as a write size hint in
shmem_read_folio_gfp() to help allocate PMD-sized large folios.
Link: https://lkml.kernel.org/r/f7e64e99a3a87a8144cc6b2f1dddf7a89c12ce44.1753926601.git.baolin.wang@linux.alibaba.com Fixes: acd7ccb284b8 ("mm: shmem: add large folio support for tmpfs") Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com> Reported-by: Patryk Kowalczyk <patryk@kowalczyk.ws> Reported-by: Ville Syrjälä <ville.syrjala@linux.intel.com> Tested-by: Patryk Kowalczyk <patryk@kowalczyk.ws> Suggested-by: Hugh Dickins <hughd@google.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Kairui Song [Mon, 28 Jul 2025 07:52:59 +0000 (15:52 +0800)]
mm/shmem, swap: improve cached mTHP handling and fix potential hang
The current swap-in code assumes that, when a swap entry in shmem mapping
is order 0, its cached folios (if present) must be order 0 too, which
turns out not always correct.
The problem is shmem_split_large_entry is called before verifying the
folio will eventually be swapped in, one possible race is:
CPU1 CPU2
shmem_swapin_folio
/* swap in of order > 0 swap entry S1 */
folio = swap_cache_get_folio
/* folio = NULL */
order = xa_get_order
/* order > 0 */
folio = shmem_swap_alloc_folio
/* mTHP alloc failure, folio = NULL */
<... Interrupted ...>
shmem_swapin_folio
/* S1 is swapped in */
shmem_writeout
/* S1 is swapped out, folio cached */
shmem_split_large_entry(..., S1)
/* S1 is split, but the folio covering it has order > 0 now */
Now any following swapin of S1 will hang: `xa_get_order` returns 0, and
folio lookup will return a folio with order > 0. The
`xa_get_order(&mapping->i_pages, index) != folio_order(folio)` will always
return false causing swap-in to return -EEXIST.
And this looks fragile. So fix this up by allowing seeing a larger folio
in swap cache, and check the whole shmem mapping range covered by the
swapin have the right swap value upon inserting the folio. And drop the
redundant tree walks before the insertion.
This will actually improve performance, as it avoids two redundant Xarray
tree walks in the hot path, and the only side effect is that in the
failure path, shmem may redundantly reallocate a few folios causing
temporary slight memory pressure.
And worth noting, it may seems the order and value check before inserting
might help reducing the lock contention, which is not true. The swap
cache layer ensures raced swapin will either see a swap cache folio or
failed to do a swapin (we have SWAP_HAS_CACHE bit even if swap cache is
bypassed), so holding the folio lock and checking the folio flag is
already good enough for avoiding the lock contention. The chance that a
folio passes the swap entry value check but the shmem mapping slot has
changed should be very low.
Link: https://lkml.kernel.org/r/20250728075306.12704-1-ryncsn@gmail.com Link: https://lkml.kernel.org/r/20250728075306.12704-2-ryncsn@gmail.com Fixes: 809bc86517cc ("mm: shmem: support large folio swap out") Signed-off-by: Kairui Song <kasong@tencent.com> Reviewed-by: Kemeng Shi <shikemeng@huaweicloud.com> Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com> Tested-by: Baolin Wang <baolin.wang@linux.alibaba.com> Cc: Baoquan He <bhe@redhat.com> Cc: Barry Song <baohua@kernel.org> Cc: Chris Li <chrisl@kernel.org> Cc: Hugh Dickins <hughd@google.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Nhat Pham <nphamcs@gmail.com> Cc: Dev Jain <dev.jain@arm.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Lorenzo Stoakes [Thu, 24 Jul 2025 13:33:56 +0000 (14:33 +0100)]
MAINTAINERS: add MM MISC section, add missing files to MISC and CORE
Add a MEMORY MANAGEMENT - MISC section to contain files that are not
described by other sections, moving all but the catch-all mm/ and
tools/mm/ from MEMORY MANAGEMENT to MEMORY MANAGEMENT - CORE and MEMORY
MANAGEMENT - MISC as appropriate.
In both sections add remaining missing files. At this point, with the
other recent MAINTAINERS changes, this should now mean that every memory
management-related file has a section and assigned maintainers/reviewers.
Finally, we copy across the maintainers/reviewers from MEMORY MANAGEMENT -
CORE to MEMORY MANAGEMENT - MISC, as it seems the two are sufficiently
related for this to be sensible.
Link: https://lkml.kernel.org/r/20250724133356.49487-1-lorenzo.stoakes@oracle.com Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org> Acked-by: Vlastimil Babka <vbabka@suse.cz> Cc: David Hildenbrand <david@redhat.com> Cc: Liam Howlett <liam.howlett@oracle.com> Cc: Michal Hocko <mhocko@suse.com> Cc: Suren Baghdasaryan <surenb@google.com> Cc: Alistair Popple <apopple@nvidia.com> Cc: Christoph Lameter (Ampere) <cl@gentwo.org> Cc: Dave Chinner <david@fromorbit.com> Cc: Dennis Zhou <dennis@kernel.org> Cc: Dev Jain <dev.jain@arm.com> Cc: Jann Horn <jannh@google.com> Cc: Muchun Song <muchun.song@linux.dev> Cc: Nico Pache <npache@redhat.com> Cc: Oscar Salvador <osalvador@suse.de> Cc: Pedro Falcato <pfalcato@suse.de> Cc: Qi Zheng <zhengqi.arch@bytedance.com> Cc: Roman Gushchin <roman.gushchin@linux.dev> Cc: Shakeel Butt <shakeel.butt@linux.dev> Cc: Tejun Heo <tj@kernel.org> Cc: Zi Yan <ziy@nvidia.com> Cc: Joshua Hahn <joshua.hahnjy@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
The trace event has not recorded the right data since it was introduced at
commit c8b360031218 ("mm: add alloc_contig_migrate_range allocation
statistics"). Remove it.
Link: https://lkml.kernel.org/r/20250722194649.4135191-1-ziy@nvidia.com Signed-off-by: Zi Yan <ziy@nvidia.com> Reported-by: kernel test robot <lkp@intel.com> Closes: https://lore.kernel.org/oe-kbuild-all/202507220742.P3SaKlI6-lkp@intel.com/ Acked-by: David Hildenbrand <david@redhat.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> Cc: Brendan Jackman <jackmanb@google.com> Cc: David Rientjes <rientjes@google.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Martin Liu <liumartin@google.com> Cc: "Masami Hiramatsu (Google)" <mhiramat@kernel.org> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: Michal Hocko <mhocko@suse.com> Cc: Richard Chang <richardycc@google.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Suren Baghdasaryan <surenb@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Enze Li [Fri, 18 Jul 2025 06:42:17 +0000 (14:42 +0800)]
selftests/damon: introduce _common.sh to host shared function
The current test scripts contain duplicated root permission checks in
multiple locations. This patch consolidates these checks into _common.sh
to eliminate code redundancy.
SeongJae Park [Sun, 20 Jul 2025 17:16:51 +0000 (10:16 -0700)]
selftests/damon/sysfs.py: test non-default parameters runtime commit
sysfs.py is testing only the default and minimum DAMON parameters. Add
another test case for more non-default additional DAMON parameters
commitment on runtime.
DAMON context commitment assertion is hard-coded for a specific test case.
Split it out into a general version that can be reused for different test
cases.
DAMON monitoring attributes commitment assertion is hard-coded for a
specific test case. Split it out into a general version that can be
reused for different test cases.
DAMOS schemes commitment assertion is hard-coded for a specific test case.
Split it out into a general version that can be reused for different test
cases.
DAMOS scheme commitment assertion is hard-coded for a specific test case.
Split it out into a general version that can be reused for different test
cases.
DamosQuota commitment assertion is hard-coded for a specific test case.
Split it out into a general version that can be reused for different test
cases.
DamosWatermarks commitment assertion is hard-coded for a specific test
case. Split it out into a general version that can be reused for
different test cases.
drgn_dump_damon_status.py is a script for dumping DAMON internal status in
json format. It is being used for seeing if DAMON parameters that are set
using _damon_sysfs.py are actually passed to DAMON in the kernel space.
It is, however, not dumping full DAMON internal status, and it makes
increasing test coverage difficult. Add damos filters dumping for more
tests.
drgn_dump_damon_status.py is a script for dumping DAMON internal status in
json format. It is being used for seeing if DAMON parameters that are set
using _damon_sysfs.py are actually passed to DAMON in the kernel space.
It is, however, not dumping full DAMON internal status, and it makes
increasing test coverage difficult. Add ctx->ops.id dumping for more
tests.
drgn_dump_damon_status.py is a script for dumping DAMON internal status in
json format. It is being used for seeing if DAMON parameters that are set
using _damon_sysfs.py are actually passed to DAMON in the kernel space.
It is, however, not dumping full DAMON internal status, and it makes
increasing test coverage difficult. Add damos->migrate_dests dumping for
more tests.
SeongJae Park [Sun, 20 Jul 2025 17:16:33 +0000 (10:16 -0700)]
selftests/damon/_damon_sysfs: support monitoring intervals goal setup
_damon_sysfs.py contains code for test-purpose DAMON sysfs interface
control. Add support of the monitoring intervals auto-tune goal setup for
more tests.
SeongJae Park [Sun, 20 Jul 2025 17:16:31 +0000 (10:16 -0700)]
selftests/damon/_damon_sysfs: support DAMOS watermarks setup
Patch series "selftests/damon/sysfs.py: test all parameters".
sysfs.py tests if DAMON sysfs interface is passing the user-requested
parameters to DAMON as expected. But only the default (minimum)
parameters are being tested. This is partially because _damon_sysfs.py,
which is the library for making the parameter requests, is not supporting
the entire parameters. The internal DAMON status dump script
(drgn_dump_damon_status.py) is also not dumping entire parameters. Extend
the test coverage by updating parameters input and status dumping scripts
to support all parameters, and writing additional tests using those.
This increased test coverage actually found one real bug
(https://lore.kernel.org/20250719181932.72944-1-sj@kernel.org).
First seven patches (1-7) extend _damon_sysfs.py for all parameters setup.
The eight patch (8) fixes _damon_sysfs.py to use correct max nr_acceses
and age values for their type. Following three patches (9-11) extend
drgn_dump_damon_status.py to dump full DAMON parameters. Following nine
patches (12-20) refactor sysfs.py for general testing code reuse, and
extend it for full parameters check. Finally, two patches (21 and 22) add
test cases in sysfs.py for full parameters testing.
This patch (of 22):
_damon_sysfs.py contains code for test-purpose DAMON sysfs interface
control. Add support of DAMOS watermarks setup for more tests.
SeongJae Park [Tue, 22 Jul 2025 06:03:30 +0000 (23:03 -0700)]
selftests/damon/sysfs.py: stop DAMON for dumping failures
Commit 4ece01897627 ("selftests/damon: add python and drgn-based DAMON
sysfs test") in mm-stable tree introduced sysfs.py that runs drgn for
dumping DAMON status. When the DAMON status dumping fails for reasons
including drgn uninstalled environment, the test fails without stopping
DAMON. Following DAMON selftests that assumes DAMON is not running when
they executed therefore fail. Catch dumping failures and stop DAMON for
that case.
Link: https://lkml.kernel.org/r/20250722060330.56068-1-sj@kernel.org Fixes: 4ece01897627 ("selftests/damon: add python and drgn-based DAMON sysfs test") Signed-off-by: SeongJae Park <sj@kernel.org> Reported-by: kernel test robot <oliver.sang@intel.com> Closes: https://lore.kernel.org/oe-lkp/202507220707.9c5d6247-lkp@intel.com Cc: Shuah Khan <shuah@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
SeongJae Park [Sun, 20 Jul 2025 18:58:22 +0000 (11:58 -0700)]
mm/damon/ops-common: ignore migration request to invalid nodes
damon_migrate_pages() tries migration even if the target node is invalid.
If users mistakenly make such invalid requests via
DAMOS_MIGRATE_{HOT,COLD} action, the below kernel BUG can happen.
Add a target node validity check in damon_migrate_pages(). The validity
check is stolen from that of do_pages_move(), which is being used for the
move_pages() system call.
Link: https://lkml.kernel.org/r/20250720185822.1451-1-sj@kernel.org Fixes: b51820ebea65 ("mm/damon/paddr: introduce DAMOS_MIGRATE_COLD action for demotion") [6.11.x] Signed-off-by: SeongJae Park <sj@kernel.org> Reviewed-by: Joshua Hahn <joshua.hahnjy@gmail.com> Cc: Honggyu Kim <honggyu.kim@sk.com> Cc: Hyeongtak Ji <hyeongtak.ji@sk.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Lorenzo Stoakes [Mon, 21 Jul 2025 15:55:30 +0000 (16:55 +0100)]
docs: update THP documentation to clarify sysfs "never" setting
Rather confusingly, setting all Transparent Huge Page sysfs settings to
"never" does not in fact result in THP being globally disabled.
Rather, it results in khugepaged being disabled, but one can still obtain
THP pages using madvise(..., MADV_COLLAPSE).
This is something that has remained poorly documented for some time, and
it is likely the received wisdom of most users of THP that never does, in
fact, mean never.
It is therefore important to highlight, very clearly, that this is not the
case.
[lorenzo.stoakes@oracle.com: update transhuge page to mention MADV_COLLAPSE] Link: https://lkml.kernel.org/r/d54d1dfb-f06d-4979-983b-73998f05867e@lucifer.local Link: https://lkml.kernel.org/r/20250721155530.75944-1-lorenzo.stoakes@oracle.com Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Acked-by: SeongJae Park <sj@kernel.org> Reviewed-by: Zi Yan <ziy@nvidia.com> Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com> Reviewed-by: Barry Song <baohua@kernel.org> Acked-by: David Hildenbrand <david@redhat.com> Cc: Dev Jain <dev.jain@arm.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Liam Howlett <liam.howlett@oracle.com> Cc: Mariano Pache <npache@redhat.com> Cc: Ryan Roberts <ryan.roberts@arm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Lorenzo Stoakes [Mon, 21 Jul 2025 17:33:26 +0000 (18:33 +0100)]
tools/testing/selftests: test MREMAP_DONTUNMAP on multiple VMA move
We support MREMAP_MAYMOVE | MREMAP_FIXED | MREMAP_DONTUNMAP for moving
multiple VMAs via mremap(), so assert that the tests pass with both
MREMAP_DONTUNMAP set and not set.
Additionally, add success = false settings when mremap() fails. This is
something that cannot realistically happen, so in no way impacted test
outcome, but it is incorrect to indicate a test pass when something has
failed.
Lorenzo Stoakes [Mon, 21 Jul 2025 17:33:25 +0000 (18:33 +0100)]
tools/testing/selftests: add mremap() shrink test for multiple VMAs
Patch series "tools/testing: expand mremap testing".
Expand our mremap() testing to further assert that behaviour is as
expected.
There is a poorly documented mremap() feature whereby it is possible to
mremap() multiple VMAs (even with gaps) when shrinking, as long as the
resultant shrunk range spans only a single VMA.
So we start by asserting this behaviour functions correctly both with an
in-place shrink and a shrink/move.
Next, we further test the newly introduced ability to mremap() multiple
VMAs when performing a MAP_FIXED move (that is without the size being
changed), firstly by asserting that MREMAP_DONTUNMAP has no bearing on
this behaviour.
Finally, we explicitly test that such moves, when splitting source VMAs,
function correctly.
This patch (of 3):
There is an apparently little-known feature of mremap() whereby, in stark
contrast to other modes (other than the recently introduced capacity to
move multiple VMAs), the input source range span multiple VMAs with gaps
between.
This is, when shrinking a VMA, whether moving it or not, and the shrink
would reduce the range to a single VMA - this is permitted, as the shrink
is actioned by an unmap.
This patch adds tests to assert that this behaves as expected.
wang lian [Thu, 17 Jul 2025 13:18:57 +0000 (21:18 +0800)]
selftests/mm: guard-regions: Use SKIP() instead of ksft_exit_skip()
To ensure only the current test is skipped on permission failure, instead
of terminating the entire test binary.
Link: https://lkml.kernel.org/r/20250717131857.59909-3-lianux.mm@gmail.com Signed-off-by: wang lian <lianux.mm@gmail.com> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Acked-by: David Hildenbrand <david@redhat.com> Reviewed-by: Mark Brown <broonie@kernel.org> Reviewed-by: Zi Yan <ziy@nvidia.com> Reviewed-by: Wei Yang <richard.weiyang@gmail.com> Cc: Christian Brauner <brauner@kernel.org> Cc: Jann Horn <jannh@google.com> Cc: Kairui Song <ryncsn@gmail.com> Cc: Liam Howlett <liam.howlett@oracle.com> Cc: SeongJae Park <sj@kernel.org> Cc: Shuah Khan <shuah@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
wang lian [Thu, 17 Jul 2025 13:18:56 +0000 (21:18 +0800)]
selftests/mm: reuse FORCE_READ to replace "asm volatile("" : "+r" (XXX));"
Patch series "selftests/mm: reuse FORCE_READ to replace "asm volatile("" :
"+r" (XXX));" and some cleanup", v2.
This series introduces a common FORCE_READ() macro to replace the cryptic
asm volatile("" : "+r" (variable)); construct used in several mm
selftests. This improves code readability and maintainability by removing
duplicated, hard-to-understand code.
This patch (of 2):
Several mm selftests use the `asm volatile("" : "+r" (variable));`
construct to force a read of a variable, preventing the compiler from
optimizing away the memory access. This idiom is cryptic and duplicated
across multiple test files.
Following a suggestion from David[1], this patch refactors this common
pattern into a FORCE_READ() macro
Dev Jain [Fri, 18 Jul 2025 09:02:44 +0000 (14:32 +0530)]
arm64: add batched versions of ptep_modify_prot_start/commit
Override the generic definition of modify_prot_start_ptes() to use
get_and_clear_full_ptes(). This helper does a TLBI only for the starting
and ending contpte block of the range, whereas the current implementation
will call ptep_get_and_clear() for every contpte block, thus doing a TLBI
on every contpte block. Therefore, we have a performance win.
The arm64 definition of pte_accessible() allows us to batch in the
errata specific case:
Dev Jain [Fri, 18 Jul 2025 09:02:43 +0000 (14:32 +0530)]
mm: optimize mprotect() by PTE batching
Use folio_pte_batch to batch process a large folio. Note that, PTE
batching here will save a few function calls, and this strategy in certain
cases (not this one) batches atomic operations in general, so we have a
performance win for all arches. This patch paves the way for patch 7
which will help us elide the TLBI per contig block on arm64.
The correctness of this patch lies on the correctness of setting the new
ptes based upon information only from the first pte of the batch (which
may also have accumulated a/d bits via modify_prot_start_ptes()).
Observe that the flag combination we pass to mprotect_folio_pte_batch()
guarantees that the batch is uniform w.r.t the soft-dirty bit and the
writable bit. Therefore, the only bits which may differ are the a/d bits.
So we only need to worry about code which is concerned about the a/d bits
of the PTEs.
Setting extra a/d bits on the new ptes where previously they were not set,
is fine - setting access bit when it was not set is not an incorrectness
problem but will only possibly delay the reclaim of the page mapped by the
pte (which is in fact intended because the kernel just operated on this
region via mprotect()!). Setting dirty bit when it was not set is again
not an incorrectness problem but will only possibly force an unnecessary
writeback.
So now we need to reason whether something can go wrong via
can_change_pte_writable(). The pte_protnone, pte_needs_soft_dirty_wp, and
userfaultfd_pte_wp cases are solved due to uniformity in the corresponding
bits guaranteed by the flag combination. The ptes all belong to the same
VMA (since callers guarantee that [start, end) will lie within the VMA)
therefore the conditional based on the VMA is also safe to batch around.
Since the dirty bit on the PTE really is just an indication that the folio
got written to - even if the PTE is not actually dirty but one of the PTEs
in the batch is, the wp-fault optimization can be made. Therefore, it is
safe to batch around pte_dirty() in can_change_shared_pte_writable() (in
fact this is better since without batching, it may happen that some ptes
aren't changed to writable just because they are not dirty, even though
the other ptes mapping the same large folio are dirty).
To batch around the PageAnonExclusive case, we must check the
corresponding condition for every single page. Therefore, from the large
folio batch, we process sub batches of ptes mapping pages with the same
PageAnonExclusive condition, and process that sub batch, then determine
and process the next sub batch, and so on. Note that this does not cause
any extra overhead; if suppose the size of the folio batch is 512, then
the sub batch processing in total will take 512 iterations, which is the
same as what we would have done before.
For pte_needs_flush():
ppc does not care about the a/d bits.
For x86, PAGE_SAVED_DIRTY is ignored. We will flush only when a/d bits
get cleared; since we can only have extra a/d bits due to batching, we
will only have an extra flush, not a case where we elide a flush due to
batching when we shouldn't have.
Link: https://lkml.kernel.org/r/20250718090244.21092-7-dev.jain@arm.com Signed-off-by: Dev Jain <dev.jain@arm.com> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Reviewed-by: Zi Yan <ziy@nvidia.com> Cc: Anshuman Khandual <anshuman.khandual@arm.com> Cc: Barry Song <baohua@kernel.org> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Christophe Leroy <christophe.leroy@csgroup.eu> Cc: David Hildenbrand <david@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jann Horn <jannh@google.com> Cc: Joey Gouly <joey.gouly@arm.com> Cc: Kevin Brodsky <kevin.brodsky@arm.com> Cc: Lance Yang <ioworker0@gmail.com> Cc: Liam Howlett <liam.howlett@oracle.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Peter Xu <peterx@redhat.com> Cc: Ryan Roberts <ryan.roberts@arm.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Will Deacon <will@kernel.org> Cc: Yang Shi <yang@os.amperecomputing.com> Cc: Yicong Yang <yangyicong@hisilicon.com> Cc: Zhenhua Huang <quic_zhenhuah@quicinc.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Dev Jain [Fri, 18 Jul 2025 09:02:42 +0000 (14:32 +0530)]
mm: split can_change_pte_writable() into private and shared parts
In preparation for patch 6 and modularizing the code in general, split
can_change_pte_writable() into private and shared VMA parts. No
functional change intended.
Link: https://lkml.kernel.org/r/20250718090244.21092-6-dev.jain@arm.com Signed-off-by: Dev Jain <dev.jain@arm.com> Suggested-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Reviewed-by: Zi Yan <ziy@nvidia.com> Cc: Anshuman Khandual <anshuman.khandual@arm.com> Cc: Barry Song <baohua@kernel.org> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Christophe Leroy <christophe.leroy@csgroup.eu> Cc: David Hildenbrand <david@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jann Horn <jannh@google.com> Cc: Joey Gouly <joey.gouly@arm.com> Cc: Kevin Brodsky <kevin.brodsky@arm.com> Cc: Lance Yang <ioworker0@gmail.com> Cc: Liam Howlett <liam.howlett@oracle.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Peter Xu <peterx@redhat.com> Cc: Ryan Roberts <ryan.roberts@arm.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Will Deacon <will@kernel.org> Cc: Yang Shi <yang@os.amperecomputing.com> Cc: Yicong Yang <yangyicong@hisilicon.com> Cc: Zhenhua Huang <quic_zhenhuah@quicinc.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Dev Jain [Fri, 18 Jul 2025 09:02:41 +0000 (14:32 +0530)]
mm: introduce FPB_RESPECT_WRITE for PTE batching infrastructure
Patch 6 ("mm: Optimize mprotect() by PTE batching") optimizes mprotect()
by batch clearing the ptes, masking in the new protections, and batch
setting the ptes. Suppose that the first pte of the batch is writable -
with the current implementation of folio_pte_batch(), it is not guaranteed
that the other ptes in the batch are already writable too, so we may
incorrectly end up setting the writable bit on all ptes via
modify_prot_commit_ptes().
Therefore, introduce FPB_RESPECT_WRITE so that all ptes in the batch are
writable or not.
Link: https://lkml.kernel.org/r/20250718090244.21092-5-dev.jain@arm.com Signed-off-by: Dev Jain <dev.jain@arm.com> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Reviewed-by: Ryan Roberts <ryan.roberts@arm.com> Reviewed-by: Zi Yan <ziy@nvidia.com> Cc: Anshuman Khandual <anshuman.khandual@arm.com> Cc: Barry Song <baohua@kernel.org> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Christophe Leroy <christophe.leroy@csgroup.eu> Cc: David Hildenbrand <david@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jann Horn <jannh@google.com> Cc: Joey Gouly <joey.gouly@arm.com> Cc: Kevin Brodsky <kevin.brodsky@arm.com> Cc: Lance Yang <ioworker0@gmail.com> Cc: Liam Howlett <liam.howlett@oracle.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Peter Xu <peterx@redhat.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Will Deacon <will@kernel.org> Cc: Yang Shi <yang@os.amperecomputing.com> Cc: Yicong Yang <yangyicong@hisilicon.com> Cc: Zhenhua Huang <quic_zhenhuah@quicinc.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Dev Jain [Fri, 18 Jul 2025 09:02:40 +0000 (14:32 +0530)]
mm: add batched versions of ptep_modify_prot_start/commit
Batch ptep_modify_prot_start/commit in preparation for optimizing
mprotect, implementing them as a simple loop over the corresponding single
pte helpers. Architecture may override these helpers.
Link: https://lkml.kernel.org/r/20250718090244.21092-4-dev.jain@arm.com Signed-off-by: Dev Jain <dev.jain@arm.com> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Reviewed-by: Barry Song <baohua@kernel.org> Reviewed-by: Ryan Roberts <ryan.roberts@arm.com> Reviewed-by: Zi Yan <ziy@nvidia.com> Cc: Anshuman Khandual <anshuman.khandual@arm.com> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Christophe Leroy <christophe.leroy@csgroup.eu> Cc: David Hildenbrand <david@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jann Horn <jannh@google.com> Cc: Joey Gouly <joey.gouly@arm.com> Cc: Kevin Brodsky <kevin.brodsky@arm.com> Cc: Lance Yang <ioworker0@gmail.com> Cc: Liam Howlett <liam.howlett@oracle.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Peter Xu <peterx@redhat.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Will Deacon <will@kernel.org> Cc: Yang Shi <yang@os.amperecomputing.com> Cc: Yicong Yang <yangyicong@hisilicon.com> Cc: Zhenhua Huang <quic_zhenhuah@quicinc.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Dev Jain [Fri, 18 Jul 2025 09:02:39 +0000 (14:32 +0530)]
mm: optimize mprotect() for MM_CP_PROT_NUMA by batch-skipping PTEs
For the MM_CP_PROT_NUMA skipping case, observe that, if we skip an
iteration due to the underlying folio satisfying any of the skip
conditions, then for all subsequent ptes which map the same folio, the
iteration will be skipped for them too. Therefore, we can optimize by
using folio_pte_batch() to batch skip the iterations.
Use prot_numa_skip() introduced in the previous patch to determine whether
we need to skip the iteration. Change its signature to have a double
pointer to a folio, which will be used by mprotect_folio_pte_batch() to
determine the number of iterations we can safely skip.
Link: https://lkml.kernel.org/r/20250718090244.21092-3-dev.jain@arm.com Signed-off-by: Dev Jain <dev.jain@arm.com> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Reviewed-by: Ryan Roberts <ryan.roberts@arm.com> Reviewed-by: Zi Yan <ziy@nvidia.com> Cc: Anshuman Khandual <anshuman.khandual@arm.com> Cc: Barry Song <baohua@kernel.org> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Christophe Leroy <christophe.leroy@csgroup.eu> Cc: David Hildenbrand <david@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jann Horn <jannh@google.com> Cc: Joey Gouly <joey.gouly@arm.com> Cc: Kevin Brodsky <kevin.brodsky@arm.com> Cc: Lance Yang <ioworker0@gmail.com> Cc: Liam Howlett <liam.howlett@oracle.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Peter Xu <peterx@redhat.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Will Deacon <will@kernel.org> Cc: Yang Shi <yang@os.amperecomputing.com> Cc: Yicong Yang <yangyicong@hisilicon.com> Cc: Zhenhua Huang <quic_zhenhuah@quicinc.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Dev Jain [Fri, 18 Jul 2025 09:02:38 +0000 (14:32 +0530)]
mm: refactor MM_CP_PROT_NUMA skipping case into new function
Patch series "Optimize mprotect() for large folios", v5.
Use folio_pte_batch() to optimize change_pte_range(). On arm64, if the
ptes are painted with the contig bit, then ptep_get() will iterate through
all 16 entries to collect a/d bits. Hence this optimization will result
in a 16x reduction in the number of ptep_get() calls. Next,
ptep_modify_prot_start() will eventually call contpte_try_unfold() on
every contig block, thus flushing the TLB for the complete large folio
range. Instead, use get_and_clear_full_ptes() so as to elide TLBIs on
each contig block, and only do them on the starting and ending contig
block.
For split folios, there will be no pte batching; the batch size returned
by folio_pte_batch() will be 1. For pagetable split folios, the ptes will
still point to the same large folio; for arm64, this results in the
optimization described above, and for other arches, a minor improvement is
expected due to a reduction in the number of function calls.
mm-selftests pass on arm64. I have some failing tests on my x86 VM
already; no new tests fail as a result of this patchset.
We use the following test cases to measure performance, mprotect()'ing the
mapped memory to read-only then read-write 40 times:
Test case 1: Mapping 1G of memory, touching it to get PMD-THPs, then
pte-mapping those THPs
Test case 2: Mapping 1G of memory with 64K mTHPs
Test case 3: Mapping 1G of memory with 4K pages
Average execution time on arm64, Apple M3:
Before the patchset:
T1: 2.1 seconds T2: 2 seconds T3: 1 second
After the patchset:
T1: 0.65 seconds T2: 0.7 seconds T3: 1.1 seconds
Observing T1/T2 and T3 before the patchset, we also remove the regression
introduced by ptep_get() on a contpte block. And, for large folios we get
an almost 74% performance improvement, albeit the trade-off being a slight
degradation in the small folio case.
For x86:
Before the patchset:
T1: 3.75 seconds T2: 3.7 seconds T3: 3.85 seconds
After the patchset:
T1: 3.7 seconds T2: 3.7 seconds T3: 3.9 seconds
So there is a minor improvement due to reduction in number of function
calls, and a slight degradation in the small folio case due to the
overhead of vm_normal_folio() + folio_test_large().
Smatch/coverity checkers report NULL mapping referencing issues[1][2][3]
every time the code is modified, because they do not understand that
mapping cannot be NULL when a folio is in page cache in the code.
Refactor the code to make it explicit.
Remove "end = -1" for anonymous folios, since after code refactoring, end
is no longer used by anonymous folio handling code.
Zi Yan [Fri, 18 Jul 2025 18:37:19 +0000 (14:37 -0400)]
mm/huge_memory: get frozen folio refcount with folio_expected_ref_count()
Instead of open coding the refcount calculation, use
folio_expected_ref_count() to calculate frozen folio refcount. Because:
1. __folio_split() does not split a folio with PG_private, so no elevated
refcount from PG_private;
2. a frozen folio in __folio_split() is fully unmapped, so folio_mapcount()
in folio_expected_ref_count() is always 0;
3. (mapping || swap_cache) ? folio_nr_pages(folio) is taken care of by
folio_expected_ref_count() too.
Link: https://lkml.kernel.org/r/20250718023000.4044406-6-ziy@nvidia.com Link: https://lkml.kernel.org/r/20250718183720.4054515-6-ziy@nvidia.com Signed-off-by: Zi Yan <ziy@nvidia.com> Suggested-by: David Hildenbrand <david@redhat.com> Acked-by: Balbir Singh <balbirs@nvidia.com> Acked-by: David Hildenbrand <david@redhat.com> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Cc: Antonio Quartulli <antonio@mandelbit.com> Cc: Baolin Wang <baolin.wang@linux.alibaba.com> Cc: Barry Song <baohua@kernel.org> Cc: Dan Carpenter <dan.carpenter@linaro.org> Cc: Dev Jain <dev.jain@arm.com> Cc: Hugh Dickins <hughd@google.com> Cc: Kirill A. Shutemov <k.shutemov@gmail.com> Cc: Liam Howlett <liam.howlett@oracle.com> Cc: Mariano Pache <npache@redhat.com> Cc: Mathew Brost <matthew.brost@intel.com> Cc: Ryan Roberts <ryan.roberts@arm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Zi Yan [Fri, 18 Jul 2025 02:29:58 +0000 (22:29 -0400)]
mm/huge_memory: convert VM_BUG* to VM_WARN* in __folio_split
These VM_BUG* can be handled gracefully without crashing kernel.
Link: https://lkml.kernel.org/r/20250718023000.4044406-5-ziy@nvidia.com Link: https://lkml.kernel.org/r/20250718183720.4054515-5-ziy@nvidia.com Signed-off-by: Zi Yan <ziy@nvidia.com> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Acked-by: David Hildenbrand <david@redhat.com> Cc: Antonio Quartulli <antonio@mandelbit.com> Cc: Balbir Singh <balbirs@nvidia.com> Cc: Baolin Wang <baolin.wang@linux.alibaba.com> Cc: Barry Song <baohua@kernel.org> Cc: Dan Carpenter <dan.carpenter@linaro.org> Cc: Dev Jain <dev.jain@arm.com> Cc: Hugh Dickins <hughd@google.com> Cc: Kirill A. Shutemov <k.shutemov@gmail.com> Cc: Liam Howlett <liam.howlett@oracle.com> Cc: Mariano Pache <npache@redhat.com> Cc: Mathew Brost <matthew.brost@intel.com> Cc: Ryan Roberts <ryan.roberts@arm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Zi Yan [Fri, 18 Jul 2025 18:37:17 +0000 (14:37 -0400)]
mm/huge_memory: deduplicate code in __folio_split()
xas unlock, remap_page(), local_irq_enable() are moved out of if branches
to deduplicate the code. While at it, add remap_flags to clean up
remap_page() call site. nr_dropped is renamed to nr_shmem_dropped, as it
becomes a variable at __folio_split() scope.
Link: https://lkml.kernel.org/r/20250718183720.4054515-4-ziy@nvidia.com Signed-off-by: Zi Yan <ziy@nvidia.com> Acked-by: David Hildenbrand <david@redhat.com> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Cc: Antonio Quartulli <antonio@mandelbit.com> Cc: Balbir Singh <balbirs@nvidia.com> Cc: Baolin Wang <baolin.wang@linux.alibaba.com> Cc: Barry Song <baohua@kernel.org> Cc: Dan Carpenter <dan.carpenter@linaro.org> Cc: Dev Jain <dev.jain@arm.com> Cc: Hugh Dickins <hughd@google.com> Cc: Kirill A. Shutemov <k.shutemov@gmail.com> Cc: Liam Howlett <liam.howlett@oracle.com> Cc: Mariano Pache <npache@redhat.com> Cc: Mathew Brost <matthew.brost@intel.com> Cc: Ryan Roberts <ryan.roberts@arm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Zi Yan [Fri, 18 Jul 2025 18:37:16 +0000 (14:37 -0400)]
mm/huge_memory: remove after_split label in __split_unmapped_folio()
Check stop_split instead to avoid the goto statement.
Link: https://lkml.kernel.org/r/20250718183720.4054515-3-ziy@nvidia.com Signed-off-by: Zi Yan <ziy@nvidia.com> Acked-by: David Hildenbrand <david@redhat.com> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Cc: Antonio Quartulli <antonio@mandelbit.com> Cc: Balbir Singh <balbirs@nvidia.com> Cc: Baolin Wang <baolin.wang@linux.alibaba.com> Cc: Barry Song <baohua@kernel.org> Cc: Dan Carpenter <dan.carpenter@linaro.org> Cc: Dev Jain <dev.jain@arm.com> Cc: Hugh Dickins <hughd@google.com> Cc: Kirill A. Shutemov <k.shutemov@gmail.com> Cc: Liam Howlett <liam.howlett@oracle.com> Cc: Mariano Pache <npache@redhat.com> Cc: Mathew Brost <matthew.brost@intel.com> Cc: Ryan Roberts <ryan.roberts@arm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Zi Yan [Fri, 18 Jul 2025 18:37:15 +0000 (14:37 -0400)]
mm/huge_memory: move unrelated code out of __split_unmapped_folio()
Patch series "__folio_split() clean up", v5.
This patchset refactors __folio_split() and __split_unmapped_folio() to:
1. make __split_unmapped_folio() reusable for splitting unmapped
folios. It avoids the need for a new boolean unmapped parameter to
guard mapping-related code when __split_unmapped_folio() is reused to
split unmapped folios.
2. improve code readability and prevent smatch/coverity checkers from
complaining about NULL mapping referencing.
An additional benefit for __split_unmapped_folio() refactoring is that
__split_unmapped_folio() could be called on after-split folios by
__folio_split(). It can enable new split methods. For example, at
deferred split time, unmapped subpages can scatter arbitrarily within a
large folio, neither uniform nor non-uniform split can maximize
after-split folio orders for mapped subpages. The hope is that by calling
__split_unmapped_folio() multiple times, a better split result can be
achieved.
This patch (of 6):
remap(), folio_ref_unfreeze(), lru_add_split_folio() are not relevant to
splitting unmapped folio operations. Move them out to __folio_split() so
that __split_unmapped_folio() only handles unmapped folio splits. This
makes __split_unmapped_folio() reusable.
Remove the swapcache folio split check code before
__split_unmapped_folio() call, since it is already checked at the
beginning of __folio_split() in uniform_split_supported() and
non_uniform_split_supported().
Along with the code move, there are some variable renames:
1. release is renamed to new_folio,
2. origin_folio is now folio, since __folio_split() has folio pointing to
the original folio already.
fs/Kconfig: enable HUGETLBFS only if ARCH_SUPPORTS_HUGETLBFS
Enable HUGETLBFS only when platform subscrbes via ARCH_SUPPORTS_HUGETLBFS.
Hence select ARCH_SUPPORTS_HUGETLBFS on existing x86 and sparc for their
continuing HUGETLBFS support. While here also just drop existing 'BROKEN'
dependency.
Link: https://lkml.kernel.org/r/20250711102934.2399533-1-anshuman.khandual@arm.com Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com> Cc: "David S. Miller" <davem@davemloft.net> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@redhat.com> Cc: Christian Brauner <brauner@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Yadan Fan [Fri, 18 Jul 2025 22:06:51 +0000 (06:06 +0800)]
mm: mempool: fix wake-up edge case bug for zero-minimum pools
The mempool wake-up path has a edge case bug that affects pools created
with min_nr=0. When a thread blocks waiting for memory from an empty pool
(curr_nr == 0), subsequent mempool_free() calls fail to wake the waiting
thread because the condition "curr_nr < min_nr" evaluates to "0 < 0" which
is false, this can cause threads to sleep indefinitely according to the
code logic.
There is at least 2 places where the mempool created with min_nr=0:
Add an explicit check in mempool_free() to handle the min_nr=0 case: when
the pool has zero minimum reserves, is currently empty, and has active
waiters, allocate the element then wake up the sleeper.
fs/proc/task_mmu: read proc/pid/maps under per-vma lock
With maple_tree supporting vma tree traversal under RCU and per-vma locks,
/proc/pid/maps can be read while holding individual vma locks instead of
locking the entire address space.
A completely lockless approach (walking vma tree under RCU) would be quite
complex with the main issue being get_vma_name() using callbacks which
might not work correctly with a stable vma copy, requiring original
(unstable) vma - see special_mapping_name() for example.
When per-vma lock acquisition fails, we take the mmap_lock for reading,
lock the vma, release the mmap_lock and continue. This fallback to mmap
read lock guarantees the reader to make forward progress even during lock
contention. This will interfere with the writer but for a very short time
while we are acquiring the per-vma lock and only when there was contention
on the vma reader is interested in.
We shouldn't see a repeated fallback to mmap read locks in practice, as
this require a very unlikely series of lock contentions (for instance due
to repeated vma split operations). However even if this did somehow
happen, we would still progress.
One case requiring special handling is when a vma changes between the time
it was found and the time it got locked. A problematic case would be if a
vma got shrunk so that its vm_start moved higher in the address space and
a new vma was installed at the beginning:
reader found: |--------VMA A--------|
VMA is modified: |-VMA B-|----VMA A----|
reader locks modified VMA A
reader reports VMA A: | gap |----VMA A----|
This would result in reporting a gap in the address space that does not
exist. To prevent this we retry the lookup after locking the vma, however
we do that only when we identify a gap and detect that the address space
was changed after we found the vma.
This change is designed to reduce mmap_lock contention and prevent a
process reading /proc/pid/maps files (often a low priority task, such as
monitoring/data collection services) from blocking address space updates.
Note that this change has a userspace visible disadvantage: it allows for
sub-page data tearing as opposed to the previous mechanism where data
tearing could happen only between pages of generated output data. Since
current userspace considers data tearing between pages to be acceptable,
we assume is will be able to handle sub-page data tearing as well.
Link: https://lkml.kernel.org/r/20250719182854.3166724-7-surenb@google.com Signed-off-by: Suren Baghdasaryan <surenb@google.com> Reviewed-by: Vlastimil Babka <vbabka@suse.cz> Cc: Alexey Dobriyan <adobriyan@gmail.com> Cc: Andrii Nakryiko <andrii@kernel.org> Cc: Christian Brauner <brauner@kernel.org> Cc: Christophe Leroy <christophe.leroy@csgroup.eu> Cc: David Hildenbrand <david@redhat.com> Cc: Jann Horn <jannh@google.com> Cc: Jeongjun Park <aha310510@gmail.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Josef Bacik <josef@toxicpanda.com> Cc: Kalesh Singh <kaleshsingh@google.com> Cc: Liam Howlett <liam.howlett@oracle.com> Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Michal Hocko <mhocko@kernel.org> Cc: Oscar Salvador <osalvador@suse.de> Cc: "Paul E . McKenney" <paulmck@kernel.org> Cc: Peter Xu <peterx@redhat.com> Cc: Ryan Roberts <ryan.roberts@arm.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Thomas Weißschuh <linux@weissschuh.net> Cc: T.J. Mercier <tjmercier@google.com> Cc: Ye Bin <yebin10@huawei.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
fs/proc/task_mmu: remove conversion of seq_file position to unsigned
Back in 2.6 era, last_addr used to be stored in seq_file->version
variable, which was unsigned long. As a result, sentinels to represent
gate vma and end of all vmas used unsigned values. In more recent kernels
we don't used seq_file->version anymore and therefore conversion from
loff_t into unsigned type is not needed. Similarly, sentinel values don't
need to be unsigned. Remove type conversion for set_file position and
change sentinel values to signed. While at it, change the hardcoded
sentinel values with named definitions for better documentation.
Link: https://lkml.kernel.org/r/20250719182854.3166724-6-surenb@google.com Signed-off-by: Suren Baghdasaryan <surenb@google.com> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Reviewed-by: Vlastimil Babka <vbabka@suse.cz> Acked-by: David Hildenbrand <david@redhat.com> Cc: Alexey Dobriyan <adobriyan@gmail.com> Cc: Andrii Nakryiko <andrii@kernel.org> Cc: Christian Brauner <brauner@kernel.org> Cc: Christophe Leroy <christophe.leroy@csgroup.eu> Cc: Jann Horn <jannh@google.com> Cc: Jeongjun Park <aha310510@gmail.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Josef Bacik <josef@toxicpanda.com> Cc: Kalesh Singh <kaleshsingh@google.com> Cc: Liam Howlett <liam.howlett@oracle.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Michal Hocko <mhocko@kernel.org> Cc: Oscar Salvador <osalvador@suse.de> Cc: "Paul E . McKenney" <paulmck@kernel.org> Cc: Peter Xu <peterx@redhat.com> Cc: Ryan Roberts <ryan.roberts@arm.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Thomas Weißschuh <linux@weissschuh.net> Cc: T.J. Mercier <tjmercier@google.com> Cc: Ye Bin <yebin10@huawei.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
selftests/proc: extend /proc/pid/maps tearing test to include vma remapping
Test that /proc/pid/maps does not report unexpected holes in the address
space when we concurrently remap a part of a vma into the middle of
another vma. This remapping results in the destination vma being split
into three parts and the part in the middle being patched back from, all
done concurrently from under the reader. We should always see either
original vma or the split one with no holes.
Link: https://lkml.kernel.org/r/20250719182854.3166724-4-surenb@google.com Signed-off-by: Suren Baghdasaryan <surenb@google.com> Cc: Alexey Dobriyan <adobriyan@gmail.com> Cc: Andrii Nakryiko <andrii@kernel.org> Cc: Christian Brauner <brauner@kernel.org> Cc: Christophe Leroy <christophe.leroy@csgroup.eu> Cc: David Hildenbrand <david@redhat.com> Cc: Jann Horn <jannh@google.com> Cc: Jeongjun Park <aha310510@gmail.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Josef Bacik <josef@toxicpanda.com> Cc: Kalesh Singh <kaleshsingh@google.com> Cc: Liam Howlett <liam.howlett@oracle.com> Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Michal Hocko <mhocko@kernel.org> Cc: Oscar Salvador <osalvador@suse.de> Cc: "Paul E . McKenney" <paulmck@kernel.org> Cc: Peter Xu <peterx@redhat.com> Cc: Ryan Roberts <ryan.roberts@arm.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Thomas Weißschuh <linux@weissschuh.net> Cc: T.J. Mercier <tjmercier@google.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Ye Bin <yebin10@huawei.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
selftests/proc: extend /proc/pid/maps tearing test to include vma resizing
Test that /proc/pid/maps does not report unexpected holes in the address
space when a vma at the edge of the page is being concurrently remapped.
This remapping results in the vma shrinking and expanding from under the
reader. We should always see either shrunk or expanded (original) version
of the vma.
Link: https://lkml.kernel.org/r/20250719182854.3166724-3-surenb@google.com Signed-off-by: Suren Baghdasaryan <surenb@google.com> Cc: Alexey Dobriyan <adobriyan@gmail.com> Cc: Andrii Nakryiko <andrii@kernel.org> Cc: Christian Brauner <brauner@kernel.org> Cc: Christophe Leroy <christophe.leroy@csgroup.eu> Cc: David Hildenbrand <david@redhat.com> Cc: Jann Horn <jannh@google.com> Cc: Jeongjun Park <aha310510@gmail.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Josef Bacik <josef@toxicpanda.com> Cc: Kalesh Singh <kaleshsingh@google.com> Cc: Liam Howlett <liam.howlett@oracle.com> Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Michal Hocko <mhocko@kernel.org> Cc: Oscar Salvador <osalvador@suse.de> Cc: "Paul E . McKenney" <paulmck@kernel.org> Cc: Peter Xu <peterx@redhat.com> Cc: Ryan Roberts <ryan.roberts@arm.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Thomas Weißschuh <linux@weissschuh.net> Cc: T.J. Mercier <tjmercier@google.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Ye Bin <yebin10@huawei.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
selftests/proc: add /proc/pid/maps tearing from vma split test
Patch series "use per-vma locks for /proc/pid/maps reads", v8.
Reading /proc/pid/maps requires read-locking mmap_lock which prevents any
other task from concurrently modifying the address space. This guarantees
coherent reporting of virtual address ranges, however it can block
important updates from happening. Oftentimes /proc/pid/maps readers are
low priority monitoring tasks and them blocking high priority tasks
results in priority inversion.
Locking the entire address space is required to present fully coherent
picture of the address space, however even current implementation does not
strictly guarantee that by outputting vmas in page-size chunks and
dropping mmap_lock in between each chunk. Address space modifications are
possible while mmap_lock is dropped and userspace reading the content is
expected to deal with possible concurrent address space modifications.
Considering these relaxed rules, holding mmap_lock is not strictly needed
as long as we can guarantee that a concurrently modified vma is reported
either in its original form or after it was modified.
This patchset switches from holding mmap_lock while reading /proc/pid/maps
to taking per-vma locks as we walk the vma tree. This reduces the
contention with tasks modifying the address space because they would have
to contend for the same vma as opposed to the entire address space.
Previous version of this patchset [1] tried to perform /proc/pid/maps
reading under RCU, however its implementation is quite complex and the
results are worse than the new version because it still relied on
mmap_lock speculation which retries if any part of the address space gets
modified. New implementaion is both simpler and results in less
contention. Note that similar approach would not work for /proc/pid/smaps
reading as it also walks the page table and that's not RCU-safe.
Paul McKenney's designed a test [2] to measure mmap/munmap latencies while
concurrently reading /proc/pid/maps. The test has a pair of processes
scanning /proc/PID/maps, and another process unmapping and remapping 4K
pages from a 128MB range of anonymous memory. At the end of each 10
second run, the latency of each mmap() or munmap() operation is measured,
and for each run the maximum and mean latency is printed. The map/unmap
process is started first, its PID is passed to the scanners, and then the
map/unmap process waits until both scanners are running before starting
its timed test. The scanners keep scanning until the specified
/proc/PID/maps file disappears.
The latest results from Paul:
Stock mm-unstable, all of the runs had maximum latencies in excess of 0.5
milliseconds, and with 80% of the runs' latencies exceeding a full
millisecond, and ranging up beyond 4 full milliseconds. In contrast, 99%
of the runs with this patch series applied had maximum latencies of less
than 0.5 milliseconds, with the single outlier at only 0.608 milliseconds.
From a median-performance (as opposed to maximum-latency) viewpoint, this
patch series also looks good, with stock mm weighing in at 11 microseconds
and patch series at 6 microseconds, better than a 2x improvement.
The patchset also adds a number of tests to check for /proc/pid/maps data
coherency. They are designed to detect any unexpected data tearing while
performing some common address space modifications (vma split, resize and
remap). Even before these changes, reading /proc/pid/maps might have
inconsistent data because the file is read page-by-page with mmap_lock
being dropped between the pages. An example of user-visible inconsistency
can be that the same vma is printed twice: once before it was modified and
then after the modifications. For example if vma was extended, it might
be found and reported twice. What is not expected is to see a gap where
there should have been a vma both before and after modification. This
patchset increases the chances of such tearing, therefore it's even more
important now to test for unexpected inconsistencies.
In [3] Lorenzo identified the following possible vma merging/splitting
scenarios:
Merges with changes to existing vmas:
1 Merge both - mapping a vma over another one and between two vmas which
can be merged after this replacement;
2. Merge left full - mapping a vma at the end of an existing one and
completely over its right neighbor;
3. Merge left partial - mapping a vma at the end of an existing one and
partially over its right neighbor;
4. Merge right full - mapping a vma before the start of an existing one
and completely over its left neighbor;
5. Merge right partial - mapping a vma before the start of an existing one
and partially over its left neighbor;
Merges without changes to existing vmas:
6. Merge both - mapping a vma into a gap between two vmas which can be
merged after the insertion;
7. Merge left - mapping a vma at the end of an existing one;
8. Merge right - mapping a vma before the start end of an existing one;
Splits
9. Split with new vma at the lower address;
10. Split with new vma at the higher address;
If such merges or splits happen concurrently with the /proc/maps reading
we might report a vma twice, once before the modification and once after
it is modified:
Case 1 might report overwritten and previous vma along with the final
merged vma;
Case 2 might report previous and the final merged vma;
Case 3 might cause us to retry once we detect the temporary gap caused by
shrinking of the right neighbor;
Case 4 might report overritten and the final merged vma;
Case 5 might cause us to retry once we detect the temporary gap caused by
shrinking of the left neighbor;
Case 6 might report previous vma and the gap along with the final marged
vma;
Case 7 might report previous and the final merged vma;
Case 8 might report the original gap and the final merged vma covering the
gap;
Case 9 might cause us to retry once we detect the temporary gap caused by
shrinking of the original vma at the vma start;
Case 10 might cause us to retry once we detect the temporary gap caused by
shrinking of the original vma at the vma end;
In all these cases the retry mechanism prevents us from reporting possible
temporary gaps.
The /proc/pid/maps file is generated page by page, with the mmap_lock
released between pages. This can lead to inconsistent reads if the
underlying vmas are concurrently modified. For instance, if a vma split
or merge occurs at a page boundary while /proc/pid/maps is being read, the
same vma might be seen twice: once before and once after the change. This
duplication is considered acceptable for userspace handling. However,
observing a "hole" where a vma should be (e.g., due to a vma being
replaced and the space temporarily being empty) is unacceptable.
Implement a test that:
1. Forks a child process which continuously modifies its address
space, specifically targeting a vma at the boundary between two pages.
2. The parent process repeatedly reads the child's /proc/pid/maps.
3. The parent process checks the last vma of the first page and the
first vma of the second page for consistency, looking for the effects
of vma splits or merges.
The test duration is configurable via DURATION environment variable
expressed in seconds. The default test duration is 5 seconds.
Example Command: DURATION=10 ./proc-maps-race
Link: https://lore.kernel.org/all/20250418174959.1431962-1-surenb@google.com/ Link: https://github.com/paulmckrcu/proc-mmap_sem-test Link: https://lore.kernel.org/all/e1863f40-39ab-4e5b-984a-c48765ffde1c@lucifer.local/ Link: https://lkml.kernel.org/r/20250719182854.3166724-1-surenb@google.com Link: https://lkml.kernel.org/r/20250719182854.3166724-2-surenb@google.com Signed-off-by: Suren Baghdasaryan <surenb@google.com> Cc: Alexey Dobriyan <adobriyan@gmail.com> Cc: Andrii Nakryiko <andrii@kernel.org> Cc: Christian Brauner <brauner@kernel.org> Cc: Christophe Leroy <christophe.leroy@csgroup.eu> Cc: David Hildenbrand <david@redhat.com> Cc: Jann Horn <jannh@google.com> Cc: Jeongjun Park <aha310510@gmail.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Josef Bacik <josef@toxicpanda.com> Cc: Kalesh Singh <kaleshsingh@google.com> Cc: Liam Howlett <liam.howlett@oracle.com> Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Michal Hocko <mhocko@kernel.org> Cc: Oscar Salvador <osalvador@suse.de> Cc: "Paul E . McKenney" <paulmck@kernel.org> Cc: Peter Xu <peterx@redhat.com> Cc: Ryan Roberts <ryan.roberts@arm.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Thomas Weißschuh <linux@weissschuh.net> Cc: T.J. Mercier <tjmercier@google.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Ye Bin <yebin10@huawei.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
A race condition is possible in stable_page_flags() where user-space is
reading /proc/kpageflags concurrently to a folio split. This may lead to
oopses or BUG_ON()s being triggered.
To fix this, this commit uses snapshot_page() in stable_page_flags() so
that stable_page_flags() works with a stable page and folio snapshots
instead.
Note that stable_page_flags() makes use of some functions that require the
original page or folio pointer to work properly (eg. is_free_budy_page()
and folio_test_idle()). Since those functions can't be used on the page
snapshot, we replace their usage with flags that were set by
snapshot_page() for this purpose.
Link: https://lkml.kernel.org/r/52c16c0f00995a812a55980c2f26848a999a34ab.1752499009.git.luizcap@redhat.com Signed-off-by: Luiz Capitulino <luizcap@redhat.com> Reviewed-by: Shivank Garg <shivankg@amd.com> Tested-by: Harry Yoo <harry.yoo@oracle.com> Acked-by: David Hildenbrand <david@redhat.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Oscar Salvador <osalvador@suse.de> Cc: SeongJae Park <sj@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Currently, the call to folio_precise_page_mapcount() from kpage_read() can
race with a folio split. When the race happens we trigger a
VM_BUG_ON_FOLIO() in folio_entire_mapcount() (see splat below).
This commit fixes this race by using snapshot_page() so that we retrieve
the folio mapcount using a folio snapshot.
This commit refactors __dump_page() into snapshot_page().
snapshot_page() tries to take a faithful snapshot of a page and its folio
representation. The snapshot is returned in the struct page_snapshot
parameter along with additional flags that are best retrieved at snapshot
creation time to reduce race windows.
This function is intended to be used by callers that need a stable
representation of a struct page and struct folio so that pointers or page
information doesn't change while working on a page.
The idea and original implementation of snapshot_page() comes from Matthew
Wilcox with suggestions for improvements from David Hildenbrand. All bugs
and misconceptions are mine.
mm/memory: introduce is_huge_zero_pfn() and use it in vm_normal_page_pmd()
Patch series "mm: introduce snapshot_page()", v3.
This series introduces snapshot_page(), a helper function that can be used
to create a snapshot of a struct page and its associated struct folio.
This function is intended to help callers with a consistent view of a a
folio while reducing the chance of encountering partially updated or
inconsistent state, such as during folio splitting which could lead to
crashes and BUG_ON()s being triggered.
This patch (of 4):
Let's avoid working with the PMD when not required. If
vm_normal_page_pmd() would be called on something that is not a present
pmd, it would already be a bug (pfn possibly garbage).
While at it, let's support passing in any pfn covered by the huge zero
folio by masking off PFN bits -- which should be rather cheap.
Kemeng Shi [Thu, 22 May 2025 12:25:54 +0000 (20:25 +0800)]
mm: swap: remove stale comment stale comment in cluster_alloc_swap_entry()
As cluster_next_cpu was already dropped, the associated comment is stale
now.
Link: https://lkml.kernel.org/r/20250522122554.12209-5-shikemeng@huaweicloud.com Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com> Reviewed-by: Kairui Song <kasong@tencent.com> Reviewed-by: Baoquan He <bhe@redhat.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
projects / thirdparty / kernel / linux.git / log
