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Shutemov" To: Jia He Cc: Andrew Morton , Matthew Wilcox , =?utf-8?B?SsOpcsO0bWU=?= Glisse , Ralph Campbell , Jason Gunthorpe , Peter Zijlstra , Dave Airlie , "Aneesh Kumar K.V" , Thomas Hellstrom , Souptick Joarder , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Catalin Marinas Subject: Re: [PATCH v2] mm: fix double page fault on arm64 if PTE_AF is cleared Message-ID: <20190910092944.3c3tducgsq673wp4@box.shutemov.name> References: <20190906135747.211836-1-justin.he@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190906135747.211836-1-justin.he@arm.com> User-Agent: NeoMutt/20180716 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Sep 06, 2019 at 09:57:47PM +0800, Jia He wrote: > When we tested pmdk unit test [1] vmmalloc_fork TEST1 in arm64 guest, there > will be a double page fault in __copy_from_user_inatomic of cow_user_page. > > Below call trace is from arm64 do_page_fault for debugging purpose > [ 110.016195] Call trace: > [ 110.016826] do_page_fault+0x5a4/0x690 > [ 110.017812] do_mem_abort+0x50/0xb0 > [ 110.018726] el1_da+0x20/0xc4 > [ 110.019492] __arch_copy_from_user+0x180/0x280 > [ 110.020646] do_wp_page+0xb0/0x860 > [ 110.021517] __handle_mm_fault+0x994/0x1338 > [ 110.022606] handle_mm_fault+0xe8/0x180 > [ 110.023584] do_page_fault+0x240/0x690 > [ 110.024535] do_mem_abort+0x50/0xb0 > [ 110.025423] el0_da+0x20/0x24 > > The pte info before __copy_from_user_inatomic is (PTE_AF is cleared): > [ffff9b007000] pgd=000000023d4f8003, pud=000000023da9b003, pmd=000000023d4b3003, pte=360000298607bd3 > > As told by Catalin: "On arm64 without hardware Access Flag, copying from > user will fail because the pte is old and cannot be marked young. So we > always end up with zeroed page after fork() + CoW for pfn mappings. we > don't always have a hardware-managed access flag on arm64." > > This patch fix it by calling pte_mkyoung. Also, the parameter is > changed because vmf should be passed to cow_user_page() > > [1] https://github.com/pmem/pmdk/tree/master/src/test/vmmalloc_fork > > Reported-by: Yibo Cai > Signed-off-by: Jia He > --- > Changes > v2: remove FAULT_FLAG_WRITE when setting pte access flag (by Catalin) > > mm/memory.c | 21 ++++++++++++++++----- > 1 file changed, 16 insertions(+), 5 deletions(-) > > diff --git a/mm/memory.c b/mm/memory.c > index e2bb51b6242e..63d4fd285e8e 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -2140,7 +2140,8 @@ static inline int pte_unmap_same(struct mm_struct *mm, pmd_t *pmd, > return same; > } > > -static inline void cow_user_page(struct page *dst, struct page *src, unsigned long va, struct vm_area_struct *vma) > +static inline void cow_user_page(struct page *dst, struct page *src, > + struct vm_fault *vmf) > { > debug_dma_assert_idle(src); > > @@ -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. 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, 0)) > + update_mmu_cache(vmf->vma, vmf->address, > + vmf->pte); > + } > + I don't see where you take ptl. -- Kirill A. Shutemov