Michael Ellerman <m...@ellerman.id.au> writes:
> 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().
>
Reviewed-by: Aneesh Kumar K.V <aneesh.ku...@linux.ibm.com>
> Fixes: b0b5e9b13047 ("powerpc/mm/radix: Add radix pte #defines")
> Cc: sta...@vger.kernel.org # v4.7+
> Reported-by: Dan Horák <d...@danny.cz>
> Link:
> https://lore.kernel.org/r/20230511095558.56663a50f86bdc4cd9770...@danny.cz
> Signed-off-by: Michael Ellerman <m...@ellerman.id.au>
> ---
> arch/powerpc/mm/book3s64/radix_pgtable.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/powerpc/mm/book3s64/radix_pgtable.c
> b/arch/powerpc/mm/book3s64/radix_pgtable.c
> index 26245aaf12b8..2297aa764ecd 100644
> --- a/arch/powerpc/mm/book3s64/radix_pgtable.c
> +++ b/arch/powerpc/mm/book3s64/radix_pgtable.c
> @@ -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);
> /*
> --
> 2.40.1
