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=-13.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 E3B56C3A5A2 for ; Wed, 4 Sep 2019 03:19:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BFFCA22CEA for ; Wed, 4 Sep 2019 03:19:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728065AbfIDDTB (ORCPT ); Tue, 3 Sep 2019 23:19:01 -0400 Received: from foss.arm.com ([217.140.110.172]:47146 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726770AbfIDDTA (ORCPT ); Tue, 3 Sep 2019 23:19:00 -0400 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 2A44F337; Tue, 3 Sep 2019 20:19:00 -0700 (PDT) Received: from [10.162.41.129] (p8cg001049571a15.blr.arm.com [10.162.41.129]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 0D7053F718; Tue, 3 Sep 2019 20:18:55 -0700 (PDT) Subject: Re: [PATCH] mm: fix double page fault on arm64 if PTE_AF is cleared To: Jia He , Andrew Morton , Matthew Wilcox , =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , 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 References: <20190904005831.153934-1-justin.he@arm.com> From: Anshuman Khandual Message-ID: Date: Wed, 4 Sep 2019 08:49:03 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20190904005831.153934-1-justin.he@arm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/04/2019 06:28 AM, 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 > > The keypoint is: we don't always have a hardware-managed access flag on > arm64. > > The root cause is in copy_one_pte, it will clear the PTE_AF for COW > pages. Generally, when it is accessed by user, the COW pages will be set > as accessed(PTE_AF bit on arm64) by hardware if hardware feature is > supported. But on some arm64 platforms, the PTE_AF needs to be set by > software. > > 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 > --- > mm/memory.c | 21 ++++++++++++++++----- > 1 file changed, 16 insertions(+), 5 deletions(-) > > diff --git a/mm/memory.c b/mm/memory.c > index e2bb51b6242e..b1f9ace2e943 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 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)) > + update_mmu_cache(vmf->vma, vmf->address, > + vmf->pte); > + } > + > if (__copy_from_user_inatomic(kaddr, uaddr, PAGE_SIZE)) Should not page fault be disabled when doing this ? Ideally it should have also called access_ok() on the user address range first. The point is that the caller of __copy_from_user_inatomic() must make sure that there cannot be any page fault while doing the actual copy. But also it should be done in generic way, something like in access_ok(). The current proposal here seems very specific to arm64 case.