mm/ptdump: take the memory hotplug lock inside ptdump_walk_pgd()

Memory hot remove unmaps and tears down various kernel page table regions
as required.  The ptdump code can race with concurrent modifications of
the kernel page tables.  When leaf entries are modified concurrently, the
dump code may log stale or inconsistent information for a VA range, but
this is otherwise not harmful.

But when intermediate levels of kernel page table are freed, the dump code
will continue to use memory that has been freed and potentially
reallocated for another purpose.  In such cases, the ptdump code may
dereference bogus addresses, leading to a number of potential problems.

To avoid the above mentioned race condition, platforms such as arm64,
riscv and s390 take memory hotplug lock, while dumping kernel page table
via the sysfs interface /sys/kernel/debug/kernel_page_tables.

Similar race condition exists while checking for pages that might have
been marked W+X via /sys/kernel/debug/kernel_page_tables/check_wx_pages
which in turn calls ptdump_check_wx().  Instead of solving this race
condition again, let's just move the memory hotplug lock inside generic
ptdump_check_wx() which will benefit both the scenarios.

Drop get_online_mems() and put_online_mems() combination from all existing
platform ptdump code paths.

Link: https://lkml.kernel.org/r/20250620052427.2092093-1-anshuman.khandual@arm.com
Fixes: bbd6ec605c0f ("arm64/mm: Enable memory hot remove")
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Dev Jain <dev.jain@arm.com>
Acked-by: Alexander Gordeev <agordeev@linux.ibm.com>	[s390]
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/arch/arm64/mm/ptdump_debugfs.c b/arch/arm64/mm/ptdump_debugfs.c
index 68bf1a125502dab30fb60903a33d65bb20eb93e6..1e308328c07966f9265fc73d07a9bf4e8979610e 100644 (file)
--- a/arch/arm64/mm/ptdump_debugfs.c
+++ b/arch/arm64/mm/ptdump_debugfs.c
@@ -1,6 +1,5 @@
 // SPDX-License-Identifier: GPL-2.0
 #include <linux/debugfs.h>
-#include <linux/memory_hotplug.h>
 #include <linux/seq_file.h>
 
 #include <asm/ptdump.h>
@@ -9,9 +8,7 @@ static int ptdump_show(struct seq_file *m, void *v)
 {
        struct ptdump_info *info = m->private;
 
-       get_online_mems();
        ptdump_walk(m, info);
-       put_online_mems();
        return 0;
 }
 DEFINE_SHOW_ATTRIBUTE(ptdump);

diff --git a/arch/riscv/mm/ptdump.c b/arch/riscv/mm/ptdump.c
index 32922550a50a3abe04c3c4227e2704760b66be9e..3b51690cc876052c4e4b13742516705e99196538 100644 (file)
--- a/arch/riscv/mm/ptdump.c
+++ b/arch/riscv/mm/ptdump.c
@@ -6,7 +6,6 @@
 #include <linux/efi.h>
 #include <linux/init.h>
 #include <linux/debugfs.h>
-#include <linux/memory_hotplug.h>
 #include <linux/seq_file.h>
 #include <linux/ptdump.h>
 
@@ -413,9 +412,7 @@ bool ptdump_check_wx(void)
 
 static int ptdump_show(struct seq_file *m, void *v)
 {
-       get_online_mems();
        ptdump_walk(m, m->private);
-       put_online_mems();
 
        return 0;
 }

diff --git a/arch/s390/mm/dump_pagetables.c b/arch/s390/mm/dump_pagetables.c
index ac604b17666095c2c78225ed70bfc4e768c4e01a..9af2aae0a5152a9d92e116df8b8bd910cf5ee528 100644 (file)
--- a/arch/s390/mm/dump_pagetables.c
+++ b/arch/s390/mm/dump_pagetables.c
@@ -247,11 +247,9 @@ static int ptdump_show(struct seq_file *m, void *v)
                .marker = markers,
        };
 
-       get_online_mems();
        mutex_lock(&cpa_mutex);
        ptdump_walk_pgd(&st.ptdump, &init_mm, NULL);
        mutex_unlock(&cpa_mutex);
-       put_online_mems();
        return 0;
 }
 DEFINE_SHOW_ATTRIBUTE(ptdump);

diff --git a/mm/ptdump.c b/mm/ptdump.c
index 61a352aa12ed8ca0db4ed0c82cdb647b6fb50e41..b600c7f864b8b420f25aa3b52787db3df22e9422 100644 (file)
--- a/mm/ptdump.c
+++ b/mm/ptdump.c
@@ -176,6 +176,7 @@ void ptdump_walk_pgd(struct ptdump_state *st, struct mm_struct *mm, pgd_t *pgd)
 {
        const struct ptdump_range *range = st->range;
 
+       get_online_mems();
        mmap_write_lock(mm);
        while (range->start != range->end) {
                walk_page_range_debug(mm, range->start, range->end,
@@ -183,6 +184,7 @@ void ptdump_walk_pgd(struct ptdump_state *st, struct mm_struct *mm, pgd_t *pgd)
                range++;
        }
        mmap_write_unlock(mm);
+       put_online_mems();
 
        /* Flush out the last page */
        st->note_page_flush(st);