On Fri, 2015-10-16 at 14:07 +0200, Laurent Dufour wrote:
> As mentioned in the commit 56eecdb912b5 ("mm: Use
> ptep/pmdp_set_numa()
> for updating _PAGE_NUMA bit"), architecture like ppc64 doesn't do
> tlb flush in set_pte/pmd functions.
>
> So when dealing with existing pte in clear_soft_dirty, the pte must
> be cleared before being modified.
Note that this is true of more than powerpc afaik. There's is a general
rule that we don't "restrict" a PTE access permissions without first
clearing it, due to various races.
> Signed-off-by: Laurent Dufour <[email protected]>
> CC: Aneesh Kumar K.V <[email protected]>
> ---
> fs/proc/task_mmu.c | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index e2d46adb54b4..c9454ee39b28 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -753,19 +753,20 @@ static inline void clear_soft_dirty(struct
> vm_area_struct *vma,
> pte_t ptent = *pte;
>
> if (pte_present(ptent)) {
> + ptent = ptep_modify_prot_start(vma->vm_mm, addr,
> pte);
> ptent = pte_wrprotect(ptent);
> ptent = pte_clear_flags(ptent, _PAGE_SOFT_DIRTY);
> + ptep_modify_prot_commit(vma->vm_mm, addr, pte,
> ptent);
> } else if (is_swap_pte(ptent)) {
> ptent = pte_swp_clear_soft_dirty(ptent);
> + set_pte_at(vma->vm_mm, addr, pte, ptent);
> }
> -
> - set_pte_at(vma->vm_mm, addr, pte, ptent);
> }
>
> static inline void clear_soft_dirty_pmd(struct vm_area_struct *vma,
> unsigned long addr, pmd_t *pmdp)
> {
> - pmd_t pmd = *pmdp;
> + pmd_t pmd = pmdp_huge_get_and_clear(vma->vm_mm, addr, pmdp);
>
> pmd = pmd_wrprotect(pmd);
> pmd = pmd_clear_flags(pmd, _PAGE_SOFT_DIRTY);
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