RE: [PATCH v5 3/3] mm: fix double page fault on arm64 if PTE_AF is cleared

[Justin He (Arm Technology China)]

Hi Catalin

> -----Original Message-----
> From: Catalin Marinas <catalin.marinas@xxxxxxx>
> Sent: 2019å9æ20æ 0:42
> To: Justin He (Arm Technology China) <Justin.He@xxxxxxx>
> Cc: Will Deacon <will@xxxxxxxxxx>; Mark Rutland
> <Mark.Rutland@xxxxxxx>; James Morse <James.Morse@xxxxxxx>; Marc
> Zyngier <maz@xxxxxxxxxx>; Matthew Wilcox <willy@xxxxxxxxxxxxx>; Kirill A.
> Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>; linux-arm-
> kernel@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; linux-
> mm@xxxxxxxxx; Suzuki Poulose <Suzuki.Poulose@xxxxxxx>; Punit
> Agrawal <punitagrawal@xxxxxxxxx>; Anshuman Khandual
> <Anshuman.Khandual@xxxxxxx>; Alex Van Brunt
> <avanbrunt@xxxxxxxxxx>; Robin Murphy <Robin.Murphy@xxxxxxx>;
> Thomas Gleixner <tglx@xxxxxxxxxxxxx>; Andrew Morton <akpm@linux-
> foundation.org>; JÃrÃme Glisse <jglisse@xxxxxxxxxx>; Ralph Campbell
> <rcampbell@xxxxxxxxxx>; hejianet@xxxxxxxxx; Kaly Xin (Arm Technology
> China) <Kaly.Xin@xxxxxxx>
> Subject: Re: [PATCH v5 3/3] mm: fix double page fault on arm64 if PTE_AF
> is cleared
>
> On Fri, Sep 20, 2019 at 12:12:04AM +0800, Jia He wrote:
> > @@ -2152,7 +2163,29 @@ 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 *)(addr & PAGE_MASK);
> > +           pte_t entry;
> > +
> > +           /* On architectures with software "accessed" bits, we would
> > +            * take a double page fault, so mark it accessed here.
> > +            */
> > +           if (arch_faults_on_old_pte() && !pte_young(vmf->orig_pte))
> {
> > +                   spin_lock(vmf->ptl);
> > +                   if (likely(pte_same(*vmf->pte, vmf->orig_pte))) {
> > +                           entry = pte_mkyoung(vmf->orig_pte);
> > +                           if (ptep_set_access_flags(vma, addr,
> > +                                                     vmf->pte, entry, 0))
> > +                                   update_mmu_cache(vma, addr, vmf-
> >pte);
> > +                   } else {
> > +                           /* Other thread has already handled the
> fault
> > +                            * and we don't need to do anything. If it's
> > +                            * not the case, the fault will be triggered
> > +                            * again on the same address.
> > +                            */
> > +                           return -1;
> > +                   }
> > +                   spin_unlock(vmf->ptl);
>
> Returning with the spinlock held doesn't normally go very well ;).
Yes, my bad. Will fix asap

--
Cheers,
Justin (Jia He)


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