From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Jia He <justin.he@arm.com>
Cc: "Catalin Marinas" <catalin.marinas@arm.com>,
"Will Deacon" <will@kernel.org>,
"Mark Rutland" <mark.rutland@arm.com>,
"James Morse" <james.morse@arm.com>,
"Marc Zyngier" <maz@kernel.org>,
"Matthew Wilcox" <willy@infradead.org>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
"Suzuki Poulose" <Suzuki.Poulose@arm.com>,
"Punit Agrawal" <punitagrawal@gmail.com>,
"Anshuman Khandual" <anshuman.khandual@arm.com>,
"Jun Yao" <yaojun8558363@gmail.com>,
"Alex Van Brunt" <avanbrunt@nvidia.com>,
"Robin Murphy" <robin.murphy@arm.com>,
"Thomas Gleixner" <tglx@linutronix.de>,
"Andrew Morton" <akpm@linux-foundation.org>,
"Jérôme Glisse" <jglisse@redhat.com>,
"Ralph Campbell" <rcampbell@nvidia.com>,
hejianet@gmail.com, "Kaly Xin" <Kaly.Xin@arm.com>
Subject: Re: [PATCH v4 3/3] mm: fix double page fault on arm64 if PTE_AF is cleared
Date: Wed, 18 Sep 2019 17:00:27 +0300 [thread overview]
Message-ID: <20190918140027.ckj32xnryyyesc23@box> (raw)
In-Reply-To: <20190918131914.38081-4-justin.he@arm.com>
On Wed, Sep 18, 2019 at 09:19:14PM +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 <Yibo.Cai@arm.com>
> Signed-off-by: Jia He <justin.he@arm.com>
> ---
> mm/memory.c | 35 ++++++++++++++++++++++++++++++-----
> 1 file changed, 30 insertions(+), 5 deletions(-)
>
> diff --git a/mm/memory.c b/mm/memory.c
> index e2bb51b6242e..d2c130a5883b 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -118,6 +118,13 @@ int randomize_va_space __read_mostly =
> 2;
> #endif
>
> +#ifndef arch_faults_on_old_pte
> +static inline bool arch_faults_on_old_pte(void)
> +{
> + return false;
> +}
> +#endif
> +
> static int __init disable_randmaps(char *s)
> {
> randomize_va_space = 0;
> @@ -2140,8 +2147,12 @@ 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)
> {
> + struct vm_area_struct *vma = vmf->vma;
> + unsigned long addr = vmf->address;
> +
> debug_dma_assert_idle(src);
>
> /*
> @@ -2152,20 +2163,34 @@ 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;
>
> /*
> * 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. On architectures with software "accessed" bits,
> + * we would take a double page fault here, 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);
> + }
I don't follow.
So if pte has changed under you, you don't set the accessed bit, but never
the less copy from the user.
What makes you think it will not trigger the same problem?
I think we need to make cow_user_page() fail in this case and caller --
wp_page_copy() -- return zero. If the fault was solved by other thread, we
are fine. If not userspace would re-fault on the same address and we will
handle the fault from the second attempt.
> + spin_unlock(vmf->ptl);
> + }
> +
> if (__copy_from_user_inatomic(kaddr, uaddr, PAGE_SIZE))
> clear_page(kaddr);
> kunmap_atomic(kaddr);
> flush_dcache_page(dst);
> } else
> - copy_user_highpage(dst, src, va, vma);
> + copy_user_highpage(dst, src, addr, vma);
> }
>
> static gfp_t __get_fault_gfp_mask(struct vm_area_struct *vma)
> @@ -2318,7 +2343,7 @@ static vm_fault_t wp_page_copy(struct vm_fault *vmf)
> vmf->address);
> if (!new_page)
> goto oom;
> - cow_user_page(new_page, old_page, vmf->address, vma);
> + cow_user_page(new_page, old_page, vmf);
> }
>
> if (mem_cgroup_try_charge_delay(new_page, mm, GFP_KERNEL, &memcg, false))
> --
> 2.17.1
>
>
--
Kirill A. Shutemov
next prev parent reply other threads:[~2019-09-18 14:00 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-18 13:19 [PATCH v4 0/3] fix double page fault on arm64 Jia He
2019-09-18 13:19 ` [PATCH v4 1/3] arm64: cpufeature: introduce helper cpu_has_hw_af() Jia He
2019-09-18 14:20 ` Matthew Wilcox
2019-09-18 16:49 ` Catalin Marinas
2019-09-18 14:20 ` Suzuki K Poulose
2019-09-18 16:45 ` Catalin Marinas
2019-09-19 1:55 ` Justin He (Arm Technology China)
2019-09-18 13:19 ` [PATCH v4 2/3] arm64: mm: implement arch_faults_on_old_pte() on arm64 Jia He
2019-09-18 13:19 ` [PATCH v4 3/3] mm: fix double page fault on arm64 if PTE_AF is cleared Jia He
2019-09-18 14:00 ` Kirill A. Shutemov [this message]
2019-09-18 18:00 ` Catalin Marinas
2019-09-19 15:00 ` Kirill A. Shutemov
2019-09-19 15:41 ` Catalin Marinas
2019-09-19 15:51 ` Kirill A. Shutemov
2019-09-19 2:16 ` Jia He
2019-09-19 14:57 ` Kirill A. Shutemov
2019-09-19 15:02 ` Justin He (Arm Technology China)
2019-09-18 19:35 ` kbuild test robot
2019-09-19 1:46 ` Justin He (Arm Technology China)
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