On Thu, Feb 27, 2025 at 2:34 AM Baolin Wang
<baolin.wang@xxxxxxxxxxxxxxxxx> wrote:
>
>
>
> On 2025/2/27 00:23, Brian Geffon wrote:
> > When handling faults for anon shmem finish_fault() will attempt to install
> > ptes for the entire folio. Unfortunately if it encounters a single
> > non-pte_none entry in that range it will bail, even if the pte that
> > triggered the fault is still pte_none. When this situation happens the
> > fault will be retried endlessly never making forward progress.
> >
> > This patch fixes this behavior and if it detects that a pte in the range
> > is not pte_none it will fall back to setting a single pte.
> >
> > Cc: stable@xxxxxxxxxxxxxxx
> > Cc: Hugh Dickins <hughd@xxxxxxxxxx>
> > Fixes: 43e027e41423 ("mm: memory: extend finish_fault() to support large folio")
> > Suggested-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
> > Reported-by: Marek Maslanka <mmaslanka@xxxxxxxxxx>
> > Signed-off-by: Brian Geffon <bgeffon@xxxxxxxxxx>
> > ---
> > mm/memory.c | 15 ++++++++++-----
> > 1 file changed, 10 insertions(+), 5 deletions(-)
> >
> > diff --git a/mm/memory.c b/mm/memory.c
> > index b4d3d4893267..b6c467fdbfa4 100644
> > --- a/mm/memory.c
> > +++ b/mm/memory.c
> > @@ -5183,7 +5183,11 @@ vm_fault_t finish_fault(struct vm_fault *vmf)
> > bool is_cow = (vmf->flags & FAULT_FLAG_WRITE) &&
> > !(vma->vm_flags & VM_SHARED);
> > int type, nr_pages;
> > - unsigned long addr = vmf->address;
> > + unsigned long addr;
> > + bool needs_fallback = false;
> > +
> > +fallback:
> > + addr = vmf->address;
> >
> > /* Did we COW the page? */
> > if (is_cow)
> > @@ -5222,7 +5226,8 @@ vm_fault_t finish_fault(struct vm_fault *vmf)
> > * approach also applies to non-anonymous-shmem faults to avoid
> > * inflating the RSS of the process.
> > */
> > - if (!vma_is_anon_shmem(vma) || unlikely(userfaultfd_armed(vma))) {
> > + if (!vma_is_anon_shmem(vma) || unlikely(userfaultfd_armed(vma)) ||
> > + unlikely(needs_fallback)) {
>
> Nit: can you align the code? Otherwise look good to me.
I mailed a v3 with adjusted alignment, I'll let Andrew decide which
variation he prefers.
>
> > nr_pages = 1;
> > } else if (nr_pages > 1) {
> > pgoff_t idx = folio_page_idx(folio, page);
> > @@ -5258,9 +5263,9 @@ vm_fault_t finish_fault(struct vm_fault *vmf)
> > ret = VM_FAULT_NOPAGE;
> > goto unlock;
> > } else if (nr_pages > 1 && !pte_range_none(vmf->pte, nr_pages)) {
> > - update_mmu_tlb_range(vma, addr, vmf->pte, nr_pages);
> > - ret = VM_FAULT_NOPAGE;
> > - goto unlock;
> > + needs_fallback = true;
> > + pte_unmap_unlock(vmf->pte, vmf->ptl);
> > + goto fallback;
> > }
> >
> > folio_ref_add(folio, nr_pages - 1);
Thanks for looking
Brian
