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arm64 fixes:

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- Do not make a clean PTE dirty in pte_mkwrite()
 
    The Arm architecture, for backwards compatibility reasons (ARMv8.0
    before in-hardware dirty bit management - DBM), uses the PTE_RDONLY
    bit to mean !dirty while the PTE_WRITE bit means DBM enabled. The
    arm64 pte_mkwrite() simply clears the PTE_RDONLY bit and this
    inadvertently makes the PTE pte_hw_dirty(). Most places making a PTE
    writable also invoke pte_mkdirty() but do_swap_page() does not and we
    end up with dirty, freshly swapped in, writeable pages.
 
  - Do not warn if the destination page is already MTE-tagged in
    copy_highpage()
 
    In the majority of the cases, a destination page copied into is
    freshly allocated without the PG_mte_tagged flag set. However, the
    folio migration may be restarted if __folio_migrate_mapping() failed,
    triggering the benign WARN_ON_ONCE().
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Merge tag 'arm64-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux

Pull arm64 fixes from Catalin Marinas:

 - Do not make a clean PTE dirty in pte_mkwrite()

   The Arm architecture, for backwards compatibility reasons (ARMv8.0
   before in-hardware dirty bit management - DBM), uses the PTE_RDONLY
   bit to mean !dirty while the PTE_WRITE bit means DBM enabled. The
   arm64 pte_mkwrite() simply clears the PTE_RDONLY bit and this
   inadvertently makes the PTE pte_hw_dirty(). Most places making a PTE
   writable also invoke pte_mkdirty() but do_swap_page() does not and we
   end up with dirty, freshly swapped in, writeable pages.

 - Do not warn if the destination page is already MTE-tagged in
   copy_highpage()

   In the majority of the cases, a destination page copied into is
   freshly allocated without the PG_mte_tagged flag set. However, the
   folio migration may be restarted if __folio_migrate_mapping() failed,
   triggering the benign WARN_ON_ONCE().

* tag 'arm64-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux:
  arm64: mte: Do not warn if the page is already tagged in copy_highpage()
  arm64, mm: avoid always making PTE dirty in pte_mkwrite()
This commit is contained in:
Linus Torvalds 2025-10-23 09:26:47 -10:00
commit 266ee584e5
2 changed files with 10 additions and 4 deletions
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3
arch/arm64/include/asm/pgtable.h
View File

@ -293,7 +293,8 @@ static inline pmd_t set_pmd_bit(pmd_t pmd, pgprot_t prot)
static inline pte_t pte_mkwrite_novma(pte_t pte)
{
pte = set_pte_bit(pte, __pgprot(PTE_WRITE));
pte = clear_pte_bit(pte, __pgprot(PTE_RDONLY));
if (pte_sw_dirty(pte))
pte = clear_pte_bit(pte, __pgprot(PTE_RDONLY));
return pte;
}

11
arch/arm64/mm/copypage.c
View File

@ -35,7 +35,7 @@ void copy_highpage(struct page *to, struct page *from)
from != folio_page(src, 0))
return;
WARN_ON_ONCE(!folio_try_hugetlb_mte_tagging(dst));
folio_try_hugetlb_mte_tagging(dst);
/*
* Populate tags for all subpages.
@ -51,8 +51,13 @@ void copy_highpage(struct page *to, struct page *from)
}
folio_set_hugetlb_mte_tagged(dst);
} else if (page_mte_tagged(from)) {
/* It's a new page, shouldn't have been tagged yet */
WARN_ON_ONCE(!try_page_mte_tagging(to));
/*
* Most of the time it's a new page that shouldn't have been
* tagged yet. However, folio migration can end up reusing the
* same page without untagging it. Ignore the warning if the
* page is already tagged.
*/
try_page_mte_tagging(to);
mte_copy_page_tags(kto, kfrom);
set_page_mte_tagged(to);