mm/memory: detect writability in restore_exclusive_pte() through can_change_pte_writa...

Let's do it just like mprotect write-upgrade or during NUMA-hinting faults
on PROT_NONE PTEs: detect if the PTE can be writable by using
can_change_pte_writable().

Set the PTE only dirty if the folio is dirty: we might not necessarily
have a write access, and setting the PTE writable doesn't require setting
the PTE dirty.

From a CPU perspective, these entries are clean.  So only set the PTE
dirty if the folios is dirty.

With this change in place, there is no need to have separate readable and
writable device-exclusive entry types, and we'll merge them next
separately.

Note that, during fork(), we first convert the device-exclusive entries
back to ordinary PTEs, and we only ever allow conversion of writable PTEs
to device-exclusive -- only mprotect can currently change them to
readable-device-exclusive.  Consequently, we always expect
PageAnonExclusive(page)==true and can_change_pte_writable()==true, unless
we are dealing with soft-dirty tracking or uffd-wp.  But reusing
can_change_pte_writable() for now is cleaner.

Link: https://lkml.kernel.org/r/20250210193801.781278-6-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Tested-by: Alistair Popple <apopple@nvidia.com>
Cc: Alex Shi <alexs@kernel.org>
Cc: Danilo Krummrich <dakr@kernel.org>
Cc: Dave Airlie <airlied@gmail.com>
Cc: Jann Horn <jannh@google.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Karol Herbst <kherbst@redhat.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Lyude <lyude@redhat.com>
Cc: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: SeongJae Park <sj@kernel.org>
Cc: Simona Vetter <simona.vetter@ffwll.ch>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Yanteng Si <si.yanteng@linux.dev>
Cc: Barry Song <v-songbaohua@oppo.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/memory.c b/mm/memory.c
index f77c10fd26b91f98c487bc22f9a1de91bd604f49..568b3afde8d20de313f4860337463018e67f5094 100644 (file)
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -723,18 +723,21 @@ static void restore_exclusive_pte(struct vm_area_struct *vma,
        struct folio *folio = page_folio(page);
        pte_t orig_pte;
        pte_t pte;
-       swp_entry_t entry;
 
        orig_pte = ptep_get(ptep);
        pte = pte_mkold(mk_pte(page, READ_ONCE(vma->vm_page_prot)));
        if (pte_swp_soft_dirty(orig_pte))
                pte = pte_mksoft_dirty(pte);
 
-       entry = pte_to_swp_entry(orig_pte);
        if (pte_swp_uffd_wp(orig_pte))
                pte = pte_mkuffd_wp(pte);
-       else if (is_writable_device_exclusive_entry(entry))
-               pte = maybe_mkwrite(pte_mkdirty(pte), vma);
+
+       if ((vma->vm_flags & VM_WRITE) &&
+           can_change_pte_writable(vma, address, pte)) {
+               if (folio_test_dirty(folio))
+                       pte = pte_mkdirty(pte);
+               pte = pte_mkwrite(pte, vma);
+       }
 
        VM_BUG_ON_FOLIO(pte_write(pte) && (!folio_test_anon(folio) &&
                                           PageAnonExclusive(page)), folio);