On Tue, Jul 11, 2023 at 1:20 PM Matthew Wilcox (Oracle)
<willy@xxxxxxxxxxxxx> wrote:
>
> Push the check down from __handle_mm_fault(). There's a mild upside to
> this patch in that we'll allocate the page tables while under the VMA
> lock rather than the mmap lock, reducing the hold time on the mmap lock,
> since the retry will find the page tables already populated.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Took some time but seems safe to me...
Reviewed-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
> ---
> mm/memory.c | 10 +++++-----
> 1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/mm/memory.c b/mm/memory.c
> index 6eda5c5f2069..52f7fdd78380 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -4924,6 +4924,11 @@ static vm_fault_t handle_pte_fault(struct vm_fault *vmf)
> {
> pte_t entry;
>
> + if ((vmf->flags & FAULT_FLAG_VMA_LOCK) && !vma_is_anonymous(vmf->vma)) {
> + vma_end_read(vmf->vma);
> + return VM_FAULT_RETRY;
> + }
> +
> if (unlikely(pmd_none(*vmf->pmd))) {
> /*
> * Leave __pte_alloc() until later: because vm_ops->fault may
> @@ -5020,11 +5025,6 @@ static vm_fault_t __handle_mm_fault(struct vm_area_struct *vma,
> p4d_t *p4d;
> vm_fault_t ret;
>
> - if ((flags & FAULT_FLAG_VMA_LOCK) && !vma_is_anonymous(vma)) {
> - vma_end_read(vma);
> - return VM_FAULT_RETRY;
> - }
> -
> pgd = pgd_offset(mm, address);
> p4d = p4d_alloc(mm, pgd, address);
> if (!p4d)
> --
> 2.39.2
>
