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mm: arm64: document why pte is not advanced in contpte_ptep_set_access_flags()

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According to David and Ryan, there isn't a bug here, even though we
don't advance the PTE entry, because __ptep_set_access_flags() only
uses the access flags from the entry.

However, we always check pte_same(pte, entry) using the first entry
in __ptep_set_access_flags(). This means that the checks from 1 to
nr - 1 are not comparing the same PTE indexes (thus, they always
return false), which can be a bit confusing. To clarify the code, let's
add some comments.

Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>
Signed-off-by: Barry Song <v-songbaohua@oppo.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Will Deacon <will@kernel.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Link: https://lore.kernel.org/r/20240905081124.9576-1-21cnbao@gmail.com
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Barry Song 2024-09-05 20:11:24 +12:00 committed by Will Deacon
parent eeb8fdfcf0
commit 70565f2be8
1 changed files with 6 additions and 0 deletions
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6
arch/arm64/mm/contpte.c
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@ -421,6 +421,12 @@ int contpte_ptep_set_access_flags(struct vm_area_struct *vma,
ptep = contpte_align_down(ptep);
start_addr = addr = ALIGN_DOWN(addr, CONT_PTE_SIZE);
/*
* We are not advancing entry because __ptep_set_access_flags()
* only consumes access flags from entry. And since we have checked
* for the whole contpte block and returned early, pte_same()
* within __ptep_set_access_flags() is likely false.
*/
for (i = 0; i < CONT_PTES; i++, ptep++, addr += PAGE_SIZE)
__ptep_set_access_flags(vma, addr, ptep, entry, 0);