Re: [PATCH v25 19/30] mm: Update can_follow_write_pte() for shadow stack

[Kirill A. Shutemov]

On Thu, Apr 15, 2021 at 03:14:08PM -0700, Yu-cheng Yu wrote:
> Can_follow_write_pte() ensures a read-only page is COWed by checking the
> FOLL_COW flag, and uses pte_dirty() to validate the flag is still valid.
> 
> Like a writable data page, a shadow stack page is writable, and becomes
> read-only during copy-on-write, but it is always dirty.  Thus, in the
> can_follow_write_pte() check, it belongs to the writable page case and
> should be excluded from the read-only page pte_dirty() check.  Apply
> the same changes to can_follow_write_pmd().
> 
> While at it, also split the long line into smaller ones.
> 
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>
> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> ---
> v25:
> - Split long line into smaller ones.
> v24:
> - Change arch_shadow_stack_mapping() to is_shadow_stack_mapping().
> 
>  mm/gup.c         | 16 ++++++++++++----
>  mm/huge_memory.c | 16 ++++++++++++----
>  2 files changed, 24 insertions(+), 8 deletions(-)
> 
> diff --git a/mm/gup.c b/mm/gup.c
> index ef7d2da9f03f..f2813cf4d07b 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -356,10 +356,18 @@ static int follow_pfn_pte(struct vm_area_struct *vma, unsigned long address,
>   * FOLL_FORCE can write to even unwritable pte's, but only
>   * after we've gone through a COW cycle and they are dirty.
>   */
> -static inline bool can_follow_write_pte(pte_t pte, unsigned int flags)
> +static inline bool can_follow_write_pte(pte_t pte, unsigned int flags,
> +					vm_flags_t vm_flags)
>  {

It might be cleaner to pass down vma pointer and dereference it within the
function: can_follow_write_pte(vma, pte, gup_flags).

Otherwise looks good to me:

Reviewed-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>

-- 
 Kirill A. Shutemov