> -----Original Message-----
> From: Catalin Marinas <catalin.marinas@xxxxxxx>
> Sent: 2019年9月4日 21:49
> To: Justin He (Arm Technology China) <Justin.He@xxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>; Matthew Wilcox
> <willy@xxxxxxxxxxxxx>; Jérôme Glisse <jglisse@xxxxxxxxxx>; Ralph
> Campbell <rcampbell@xxxxxxxxxx>; Jason Gunthorpe <jgg@xxxxxxxx>;
> Peter Zijlstra <peterz@xxxxxxxxxxxxx>; Dave Airlie <airlied@xxxxxxxxxx>;
> Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx>; Thomas Hellstrom
> <thellstrom@xxxxxxxxxx>; Souptick Joarder <jrdr.linux@xxxxxxxxx>;
> linux-mm <linux-mm@xxxxxxxxx>; Linux Kernel Mailing List <linux-
> kernel@xxxxxxxxxxxxxxx>
> Subject: Re: [PATCH] mm: fix double page fault on arm64 if PTE_AF is
> cleared
>
> On Wed, 4 Sep 2019 at 01:59, Jia He <justin.he@xxxxxxx> wrote:
> > @@ -2152,20 +2153,30 @@ static inline void cow_user_page(struct page
> *dst, struct page *src, unsigned lo
> > */
> > if (unlikely(!src)) {
> > void *kaddr = kmap_atomic(dst);
> > - void __user *uaddr = (void __user *)(va & PAGE_MASK);
> > + void __user *uaddr = (void __user *)(vmf->address &
> PAGE_MASK);
> > + pte_t entry;
> >
> > /*
> > * 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 here. so makes pte young here
> > */
> > + if (!pte_young(vmf->orig_pte)) {
> > + entry = pte_mkyoung(vmf->orig_pte);
> > + if (ptep_set_access_flags(vmf->vma, vmf->address,
> > + vmf->pte, entry, vmf->flags & FAULT_FLAG_WRITE))
>
> I think you need to pass dirty = 0 to ptep_set_access_flags() rather
> than the vmf->flags & FAULT_FLAG_WRITE. This is copying from the user
> address into a kernel mapping and the fault you want to prevent is a
> read access on uaddr via __copy_from_user_inatomic(). The pte will be
> made writable in the wp_page_copy() function.
Ok, thanks
--
Cheers,
Justin (Jia He)
>
> --
> Catalin
IMPORTANT NOTICE: The contents of this email and any attachments are confidential and may also be privileged. If you are not the intended recipient, please notify the sender immediately and do not disclose the contents to any other person, use it for any purpose, or store or copy the information in any medium. Thank you.
