On Thu, Apr 01, 2021 at 03:10:54PM -0700, Yu-cheng Yu wrote:
> In change_pte_range(), when a PTE is changed for prot_numa, _PAGE_RW is
> preserved to avoid the additional write fault after the NUMA hinting fault.
> However, pte_write() now includes both normal writable and shadow stack
> (RW=0, Dirty=1) PTEs, but the latter does not have _PAGE_RW and has no need
> to preserve it.
>
> Exclude shadow stack from preserve_write test, and apply the same change to
> change_huge_pmd().
>
> Signed-off-by: Yu-cheng Yu <[email protected]>
> Cc: Kirill A. Shutemov <[email protected]>
> ---
> v24:
> - Change arch_shadow_stack_mapping() to is_shadow_stack_mapping().
>
> mm/huge_memory.c | 7 ++++++-
> mm/mprotect.c | 9 ++++++++-
> 2 files changed, 14 insertions(+), 2 deletions(-)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 65fc0aedd577..1d41138c4f74 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -1812,12 +1812,17 @@ int change_huge_pmd(struct vm_area_struct *vma, pmd_t
> *pmd,
> bool prot_numa = cp_flags & MM_CP_PROT_NUMA;
> bool uffd_wp = cp_flags & MM_CP_UFFD_WP;
> bool uffd_wp_resolve = cp_flags & MM_CP_UFFD_WP_RESOLVE;
> + bool shstk = is_shadow_stack_mapping(vma->vm_flags);
>
> ptl = __pmd_trans_huge_lock(pmd, vma);
> if (!ptl)
> return 0;
>
> - preserve_write = prot_numa && pmd_write(*pmd);
> + /*
> + * Preserve only normal writable huge PMD, but not shadow
> + * stack (RW=0, Dirty=1).
> + */
> + preserve_write = prot_numa && pmd_write(*pmd) && !shstk;
New variable seems unnecessary. What about just:
if (is_shadow_stack_mapping(vma->vm_flags))
preserve_write = false;
?
> ret = 1;
>
> #ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
> diff --git a/mm/mprotect.c b/mm/mprotect.c
> index c1ce78d688b6..550448dc5ff1 100644
> --- a/mm/mprotect.c
> +++ b/mm/mprotect.c
> @@ -75,7 +75,14 @@ static unsigned long change_pte_range(struct
> vm_area_struct *vma, pmd_t *pmd,
> oldpte = *pte;
> if (pte_present(oldpte)) {
> pte_t ptent;
> - bool preserve_write = prot_numa && pte_write(oldpte);
> + bool shstk = is_shadow_stack_mapping(vma->vm_flags);
> + bool preserve_write;
> +
> + /*
> + * Preserve only normal writable PTE, but not shadow
> + * stack (RW=0, Dirty=1).
> + */
> + preserve_write = prot_numa && pte_write(oldpte) &&
> !shstk;
Ditto.
>
> /*
> * Avoid trapping faults against the zero or KSM
> --
> 2.21.0
>
>
--
Kirill A. Shutemov
