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=-5.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT 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 0288CC10F11 for ; Tue, 23 Apr 2019 03:00:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BC8A320811 for ; Tue, 23 Apr 2019 03:00:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731278AbfDWDAq (ORCPT ); Mon, 22 Apr 2019 23:00:46 -0400 Received: from mx1.redhat.com ([209.132.183.28]:57818 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728527AbfDWDAq (ORCPT ); Mon, 22 Apr 2019 23:00:46 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id B3009307D840; Tue, 23 Apr 2019 03:00:44 +0000 (UTC) Received: from xz-x1 (ovpn-12-175.pek2.redhat.com [10.72.12.175]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 23A585C1B5; Tue, 23 Apr 2019 03:00:33 +0000 (UTC) Date: Tue, 23 Apr 2019 11:00:30 +0800 From: Peter Xu To: Jerome Glisse Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, David Hildenbrand , Hugh Dickins , Maya Gokhale , Pavel Emelyanov , Johannes Weiner , Martin Cracauer , Shaohua Li , Andrea Arcangeli , Mike Kravetz , Denis Plotnikov , Mike Rapoport , Marty McFadden , Mel Gorman , "Kirill A . Shutemov" , "Dr . David Alan Gilbert" Subject: Re: [PATCH v3 14/28] userfaultfd: wp: handle COW properly for uffd-wp Message-ID: <20190423030030.GA21301@xz-x1> References: <20190320020642.4000-1-peterx@redhat.com> <20190320020642.4000-15-peterx@redhat.com> <20190418202558.GK3288@redhat.com> <20190419062650.GF13323@xz-x1> <20190419150253.GA3311@redhat.com> <20190422122010.GA25896@xz-x1> <20190422145402.GB3450@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20190422145402.GB3450@redhat.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.48]); Tue, 23 Apr 2019 03:00:45 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Apr 22, 2019 at 10:54:02AM -0400, Jerome Glisse wrote: > On Mon, Apr 22, 2019 at 08:20:10PM +0800, Peter Xu wrote: > > On Fri, Apr 19, 2019 at 11:02:53AM -0400, Jerome Glisse wrote: > > > > [...] > > > > > > > > + if (uffd_wp_resolve) { > > > > > > + /* If the fault is resolved already, skip */ > > > > > > + if (!pte_uffd_wp(*pte)) > > > > > > + continue; > > > > > > + page = vm_normal_page(vma, addr, oldpte); > > > > > > + if (!page || page_mapcount(page) > 1) { > > > > > > + struct vm_fault vmf = { > > > > > > + .vma = vma, > > > > > > + .address = addr & PAGE_MASK, > > > > > > + .page = page, > > > > > > + .orig_pte = oldpte, > > > > > > + .pmd = pmd, > > > > > > + /* pte and ptl not needed */ > > > > > > + }; > > > > > > + vm_fault_t ret; > > > > > > + > > > > > > + if (page) > > > > > > + get_page(page); > > > > > > + arch_leave_lazy_mmu_mode(); > > > > > > + pte_unmap_unlock(pte, ptl); > > > > > > + ret = wp_page_copy(&vmf); > > > > > > + /* PTE is changed, or OOM */ > > > > > > + if (ret == 0) > > > > > > + /* It's done by others */ > > > > > > + continue; > > > > > > > > > > This is wrong if ret == 0 you still need to remap the pte before > > > > > continuing as otherwise you will go to next pte without the page > > > > > table lock for the directory. So 0 case must be handled after > > > > > arch_enter_lazy_mmu_mode() below. > > > > > > > > > > Sorry i should have catch that in previous review. > > > > > > > > My fault to not have noticed it since the very beginning... thanks for > > > > spotting that. > > > > > > > > I'm squashing below changes into the patch: > > > > > > > > > Well thinking of this some more i think you should use do_wp_page() and > > > not wp_page_copy() it would avoid bunch of code above and also you are > > > not properly handling KSM page or page in the swap cache. Instead of > > > duplicating same code that is in do_wp_page() it would be better to call > > > it here. > > > > Yeah it makes sense to me. Then here's my plan: > > > > - I'll need to drop previous patch "export wp_page_copy" since then > > it'll be not needed > > > > - I'll introduce another patch to split current do_wp_page() and > > introduce function "wp_page_copy_cont" (better suggestion on the > > naming would be welcomed) which contains most of the wp handling > > that'll be needed for change_pte_range() in this patch and isolate > > the uffd handling: > > > > static vm_fault_t do_wp_page(struct vm_fault *vmf) > > __releases(vmf->ptl) > > { > > struct vm_area_struct *vma = vmf->vma; > > > > if (userfaultfd_pte_wp(vma, *vmf->pte)) { > > pte_unmap_unlock(vmf->pte, vmf->ptl); > > return handle_userfault(vmf, VM_UFFD_WP); > > } > > > > return do_wp_page_cont(vmf); > > } > > > > Then I can probably use do_wp_page_cont() in this patch. > > Instead i would keep the do_wp_page name and do: > static vm_fault_t do_userfaultfd_wp_page(struct vm_fault *vmf) { > ... // what you have above > return do_wp_page(vmf); > } > > Naming wise i think it would be better to keep do_wp_page() as > is. In case I misunderstood... what I've proposed will be simply: diff --git a/mm/memory.c b/mm/memory.c index 64bd8075f054..ab98a1eb4702 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -2497,6 +2497,14 @@ static vm_fault_t do_wp_page(struct vm_fault *vmf) return handle_userfault(vmf, VM_UFFD_WP); } + return do_wp_page_cont(vmf); +} + +vm_fault_t do_wp_page_cont(struct vm_fault *vmf) + __releases(vmf->ptl) +{ + struct vm_area_struct *vma = vmf->vma; + vmf->page = vm_normal_page(vma, vmf->address, vmf->orig_pte); if (!vmf->page) { /* And the other proposal is: diff --git a/mm/memory.c b/mm/memory.c index 64bd8075f054..a73792127553 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -2469,6 +2469,8 @@ static vm_fault_t wp_page_shared(struct vm_fault *vmf) return VM_FAULT_WRITE; } +static vm_fault_t do_wp_page(struct vm_fault *vmf); + /* * This routine handles present pages, when users try to write * to a shared page. It is done by copying the page to a new address @@ -2487,7 +2489,7 @@ static vm_fault_t wp_page_shared(struct vm_fault *vmf) * but allow concurrent faults), with pte both mapped and locked. * We return with mmap_sem still held, but pte unmapped and unlocked. */ -static vm_fault_t do_wp_page(struct vm_fault *vmf) +static vm_fault_t do_userfaultfd_wp_page(struct vm_fault *vmf) __releases(vmf->ptl) { struct vm_area_struct *vma = vmf->vma; @@ -2497,6 +2499,14 @@ static vm_fault_t do_wp_page(struct vm_fault *vmf) return handle_userfault(vmf, VM_UFFD_WP); } + return do_wp_page(vmf); +} + +static vm_fault_t do_wp_page(struct vm_fault *vmf) + __releases(vmf->ptl) +{ + struct vm_area_struct *vma = vmf->vma; + vmf->page = vm_normal_page(vma, vmf->address, vmf->orig_pte); if (!vmf->page) { /* @@ -2869,7 +2879,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) } if (vmf->flags & FAULT_FLAG_WRITE) { - ret |= do_wp_page(vmf); + ret |= do_userfaultfd_wp_page(vmf); if (ret & VM_FAULT_ERROR) ret &= VM_FAULT_ERROR; goto out; @@ -3831,7 +3841,7 @@ static vm_fault_t handle_pte_fault(struct vm_fault *vmf) goto unlock; if (vmf->flags & FAULT_FLAG_WRITE) { if (!pte_write(entry)) - return do_wp_page(vmf); + return do_userfaultfd_wp_page(vmf); entry = pte_mkdirty(entry); } entry = pte_mkyoung(entry); I would prefer the 1st approach since it not only contains fewer lines of changes because it does not touch callers, and also the naming in the 2nd approach can be a bit confusing (calling do_userfaultfd_wp_page in handle_pte_fault may let people think of an userfault-only path but actually it covers the general path). But if you really like the 2nd one I can use that too. Thanks, -- Peter Xu