> On Aug 22, 2024, at 15:13, Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx> wrote:
>
> In handle_pte_fault(), we may modify the vmf->pte after acquiring the
> vmf->ptl, so convert it to using pte_offset_map_rw_nolock(). But since we
> will do the pte_same() check, so there is no need to get pmdval to do
> pmd_same() check, just pass a dummy variable to it.
>
> Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
Reviewed-by: Muchun Song <muchun.song@xxxxxxxxx>
A nit below.
> ---
> mm/memory.c | 12 ++++++++++--
> 1 file changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/mm/memory.c b/mm/memory.c
> index 93c0c25433d02..7b6071a0e21e2 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -5499,14 +5499,22 @@ static vm_fault_t handle_pte_fault(struct vm_fault *vmf)
> vmf->pte = NULL;
> vmf->flags &= ~FAULT_FLAG_ORIG_PTE_VALID;
> } else {
> + pmd_t dummy_pmdval;
> +
> /*
> * A regular pmd is established and it can't morph into a huge
> * pmd by anon khugepaged, since that takes mmap_lock in write
> * mode; but shmem or file collapse to THP could still morph
> * it into a huge pmd: just retry later if so.
> + *
> + * Use the maywrite version to indicate that vmf->pte will be
Not "will be", should be "may be".
> + * modified, but since we will use pte_same() to detect the
> + * change of the pte entry, there is no need to get pmdval, so
> + * just pass a dummy variable to it.
> */
> - vmf->pte = pte_offset_map_nolock(vmf->vma->vm_mm, vmf->pmd,
> - vmf->address, &vmf->ptl);
> + vmf->pte = pte_offset_map_rw_nolock(vmf->vma->vm_mm, vmf->pmd,
> + vmf->address, &dummy_pmdval,
> + &vmf->ptl);
> if (unlikely(!vmf->pte))
> return 0;
> vmf->orig_pte = ptep_get_lockless(vmf->pte);
> --
> 2.20.1
>
