From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-14.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B0C17C49ED7 for ; Fri, 20 Sep 2019 02:22:03 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 74F23207FC for ; Fri, 20 Sep 2019 02:22:03 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 74F23207FC Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 206398E000E; Thu, 19 Sep 2019 22:22:03 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 1DD438E0003; Thu, 19 Sep 2019 22:22:03 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 0F1CC8E000E; Thu, 19 Sep 2019 22:22:03 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0198.hostedemail.com [216.40.44.198]) by kanga.kvack.org (Postfix) with ESMTP id DBAD78E0003 for ; Thu, 19 Sep 2019 22:22:02 -0400 (EDT) Received: from smtpin18.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with SMTP id 463BC181AC9B4 for ; Fri, 20 Sep 2019 02:22:02 +0000 (UTC) X-FDA: 75953698884.18.shelf86_11bc1e535392f X-HE-Tag: shelf86_11bc1e535392f X-Filterd-Recvd-Size: 7011 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf08.hostedemail.com (Postfix) with ESMTP for ; Fri, 20 Sep 2019 02:22:01 +0000 (UTC) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 215021570; Thu, 19 Sep 2019 19:22:00 -0700 (PDT) Received: from localhost.localdomain (entos-thunderx2-02.shanghai.arm.com [10.169.40.54]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id A51293F67D; Thu, 19 Sep 2019 19:21:55 -0700 (PDT) From: Jia He To: Catalin Marinas , Will Deacon , Mark Rutland , James Morse , Marc Zyngier , Matthew Wilcox , "Kirill A. Shutemov" , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Suzuki Poulose Cc: Punit Agrawal , Anshuman Khandual , Jun Yao , Alex Van Brunt , Robin Murphy , Thomas Gleixner , Andrew Morton , =?UTF-8?q?J=C3=A9r=C3=B4me=20Glisse?= , Ralph Campbell , hejianet@gmail.com, Kaly Xin , Jia He Subject: [PATCH v6 3/3] mm: fix double page fault on arm64 if PTE_AF is cleared Date: Fri, 20 Sep 2019 10:21:32 +0800 Message-Id: <20190920022132.149467-4-justin.he@arm.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20190920022132.149467-1-justin.he@arm.com> References: <20190920022132.149467-1-justin.he@arm.com> X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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() Add a WARN_ON_ONCE when __copy_from_user_inatomic() returns error in case there can be some obscure use-case.(by Kirill) [1] https://github.com/pmem/pmdk/tree/master/src/test/vmmalloc_fork Reported-by: Yibo Cai Signed-off-by: Jia He --- mm/memory.c | 65 ++++++++++++++++++++++++++++++++++++++++++++++++----- 1 file changed, 59 insertions(+), 6 deletions(-) diff --git a/mm/memory.c b/mm/memory.c index e2bb51b6242e..7c38c1ce5440 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 int 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); /* @@ -2151,21 +2162,52 @@ static inline void cow_user_page(struct page *dst, struct page *src, unsigned lo * fails, we just zero-fill it. Live with it. */ if (unlikely(!src)) { - void *kaddr = kmap_atomic(dst); - void __user *uaddr = (void __user *)(va & PAGE_MASK); + void *kaddr; + 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. + */ + spin_unlock(vmf->ptl); + return -1; + } + spin_unlock(vmf->ptl); + } + kaddr = kmap_atomic(dst); /* * 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. */ - if (__copy_from_user_inatomic(kaddr, uaddr, PAGE_SIZE)) + if (__copy_from_user_inatomic(kaddr, uaddr, PAGE_SIZE)) { + /* Give a warn in case there can be some obscure + * use-case + */ + WARN_ON_ONCE(1); 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); + + return 0; } static gfp_t __get_fault_gfp_mask(struct vm_area_struct *vma) @@ -2318,7 +2360,16 @@ 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); + + if (cow_user_page(new_page, old_page, vmf)) { + /* COW failed, if the fault was solved by other, + * it's fine. If not, userspace would re-fault on + * the same address and we will handle the fault + * from the second attempt. + */ + put_page(new_page); + goto normal; + } } if (mem_cgroup_try_charge_delay(new_page, mm, GFP_KERNEL, &memcg, false)) @@ -2420,6 +2471,8 @@ static vm_fault_t wp_page_copy(struct vm_fault *vmf) } put_page(old_page); } + +normal: return page_copied ? VM_FAULT_WRITE : 0; oom_free_new: put_page(new_page); -- 2.17.1