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powerpc/64s/radix: Fix soft dirty tracking

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It was reported that soft dirty tracking doesn't work when using the
Radix MMU.

The tracking is supposed to work by clearing the soft dirty bit for a
mapping and then write protecting the PTE. If/when the page is written
to, a page fault occurs and the soft dirty bit is added back via
pte_mkdirty(). For example in wp_page_reuse():

	entry = maybe_mkwrite(pte_mkdirty(entry), vma);
	if (ptep_set_access_flags(vma, vmf->address, vmf->pte, entry, 1))
		update_mmu_cache(vma, vmf->address, vmf->pte);

Unfortunately on radix _PAGE_SOFTDIRTY is being dropped by
radix__ptep_set_access_flags(), called from ptep_set_access_flags(),
meaning the soft dirty bit is not set even though the page has been
written to.

Fix it by adding _PAGE_SOFTDIRTY to the set of bits that are able to be
changed in radix__ptep_set_access_flags().

Fixes: b0b5e9b130 ("powerpc/mm/radix: Add radix pte #defines")
Cc: stable@vger.kernel.org # v4.7+
Reported-by: Dan Horák <dan@danny.cz>
Link: https://lore.kernel.org/r/20230511095558.56663a50f86bdc4cd97700b7@danny.cz
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230511114224.977423-1-mpe@ellerman.id.au
This commit is contained in:
Michael Ellerman 2023-05-11 21:42:24 +10:00
parent 536d948a8d
commit 66b2ca0862
1 changed files with 2 additions and 2 deletions
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4
arch/powerpc/mm/book3s64/radix_pgtable.c
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@ -1040,8 +1040,8 @@ void radix__ptep_set_access_flags(struct vm_area_struct *vma, pte_t *ptep,
pte_t entry, unsigned long address, int psize)
{
struct mm_struct *mm = vma->vm_mm;
unsigned long set = pte_val(entry) & (_PAGE_DIRTY | _PAGE_ACCESSED |
_PAGE_RW | _PAGE_EXEC);
unsigned long set = pte_val(entry) & (_PAGE_DIRTY | _PAGE_SOFT_DIRTY |
_PAGE_ACCESSED | _PAGE_RW | _PAGE_EXEC);
unsigned long change = pte_val(entry) ^ pte_val(*ptep);
/*