Messages in this thread | | | Date | Fri, 6 Sep 2019 07:57:42 -0700 | From | Matthew Wilcox <> | Subject | Re: [PATCH v2] mm: fix double page fault on arm64 if PTE_AF is cleared |
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On Fri, Sep 06, 2019 at 09:57:47PM +0800, Jia He wrote: > * This really shouldn't fail, because the page is there > * in the page tables. But it might just be unreadable, > * in which case we just give up and fill the result with > - * zeroes. > + * zeroes. If PTE_AF is cleared on arm64, it might > + * cause double page fault. So makes pte young here
How about: * zeroes. On architectures with software "accessed" bits, * we would take a double page fault here, so mark it * accessed here.
> */ > + if (!pte_young(vmf->orig_pte)) {
Let's guard this with:
if (arch_sw_access_bit && !pte_young(vmf->orig_pte)) {
#define arch_sw_access_bit 0 by default and have arm64 override it (either to a variable or a constant ... your choice). Also, please somebody decide on a better name than arch_sw_access_bit.
> + entry = pte_mkyoung(vmf->orig_pte); > + if (ptep_set_access_flags(vmf->vma, vmf->address, > + vmf->pte, entry, 0))
This indentation is wrong; it makes vmf->pte look like part of the subsequent statement instead of part of the condition.
> + update_mmu_cache(vmf->vma, vmf->address, > + vmf->pte); > + } > +
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