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mm/madvise: preserve VMA_SOFTDIRTY_BIT when changing anonymous names

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When changing the anonymous VMA name, madvise_update_vma() calls
vma_modify_name() to possibly merge with adjacent VMAs. We don't call
vma_modify_flags() and consequently don't obtain the new VMA flags.

Later in the function we update the VMA flags to the stale new_vma_flags
we obtained before. This can result in us losing the VMA_SOFTDIRTY_BIT
flag set on a VMA we just merged with.

There is no need to update the VMA flags at all, so just exit early. This
skips calling khugepaged_enter_vma(), but since the flags didn't change
this is fine.

[ljs@kernel.org: minor edit of commit message, rebased]
Link: https://lore.kernel.org/20261023-fix-vma-atomic-v1-3-8ff4fae1fc85@kernel.org
Fixes: 9a10064f56 ("mm: add a field to store names for private anonymous memory")
Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Reviewed-by: Pedro Falcato <pfalcato@suse.de>
Tested-by: Gregory Price (Meta) <gourry@gourry.net>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Jann Horn <jannh@google.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: SJ Park <sj@kernel.org>
Cc: Kees Cook <kees@kernel.org>
Cc: Colin Cross <ccross@google.com>
Cc: <stable@vger.kernel.org>
This commit is contained in:
David Hildenbrand (Arm) 2026-10-23 14:47:29 +01:00 committed by Andrew Morton
parent 769417e410
commit 652f15be3c
1 changed files with 3 additions and 3 deletions
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6
mm/madvise.c
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@ -177,6 +177,9 @@ static int madvise_update_vma(vm_flags_t new_flags,
/* vm_flags is protected by the mmap_lock held in write mode. */
vma_start_write(vma);
if (set_new_anon_name)
return replace_anon_vma_name(vma, anon_name);
vma_overwrite_flags(vma, new_vma_flags);
/*
* If the vma become good for khugepaged to scan,
@ -186,9 +189,6 @@ static int madvise_update_vma(vm_flags_t new_flags,
if (vma_flags_test(&new_vma_flags, VMA_HUGEPAGE_BIT))
khugepaged_enter_vma(vma, vma_flags_to_legacy(new_vma_flags));
if (set_new_anon_name)
return replace_anon_vma_name(vma, anon_name);
return 0;
}