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=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED 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 2B984C282CE for ; Tue, 12 Feb 2019 02:58:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 01F3B21773 for ; Tue, 12 Feb 2019 02:58:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728089AbfBLC6E (ORCPT ); Mon, 11 Feb 2019 21:58:04 -0500 Received: from mx1.redhat.com ([209.132.183.28]:57278 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726226AbfBLC6D (ORCPT ); Mon, 11 Feb 2019 21:58:03 -0500 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id DB26BE6A60; Tue, 12 Feb 2019 02:58:02 +0000 (UTC) Received: from xz-x1.nay.redhat.com (dhcp-14-116.nay.redhat.com [10.66.14.116]) by smtp.corp.redhat.com (Postfix) with ESMTP id 62382600C6; Tue, 12 Feb 2019 02:57:56 +0000 (UTC) From: Peter Xu To: linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: David Hildenbrand , Hugh Dickins , Maya Gokhale , Jerome Glisse , Pavel Emelyanov , Johannes Weiner , peterx@redhat.com, Martin Cracauer , Shaohua Li , Marty McFadden , Andrea Arcangeli , Mike Kravetz , Denis Plotnikov , Mike Rapoport , Mel Gorman , "Kirill A . Shutemov" , "Dr . David Alan Gilbert" Subject: [PATCH v2 07/26] userfaultfd: wp: hook userfault handler to write protection fault Date: Tue, 12 Feb 2019 10:56:13 +0800 Message-Id: <20190212025632.28946-8-peterx@redhat.com> In-Reply-To: <20190212025632.28946-1-peterx@redhat.com> References: <20190212025632.28946-1-peterx@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.38]); Tue, 12 Feb 2019 02:58:03 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Andrea Arcangeli There are several cases write protection fault happens. It could be a write to zero page, swaped page or userfault write protected page. When the fault happens, there is no way to know if userfault write protect the page before. Here we just blindly issue a userfault notification for vma with VM_UFFD_WP regardless if app write protects it yet. Application should be ready to handle such wp fault. v1: From: Shaohua Li v2: Handle the userfault in the common do_wp_page. If we get there a pagetable is present and readonly so no need to do further processing until we solve the userfault. In the swapin case, always swapin as readonly. This will cause false positive userfaults. We need to decide later if to eliminate them with a flag like soft-dirty in the swap entry (see _PAGE_SWP_SOFT_DIRTY). hugetlbfs wouldn't need to worry about swapouts but and tmpfs would be handled by a swap entry bit like anonymous memory. The main problem with no easy solution to eliminate the false positives, will be if/when userfaultfd is extended to real filesystem pagecache. When the pagecache is freed by reclaim we can't leave the radix tree pinned if the inode and in turn the radix tree is reclaimed as well. The estimation is that full accuracy and lack of false positives could be easily provided only to anonymous memory (as long as there's no fork or as long as MADV_DONTFORK is used on the userfaultfd anonymous range) tmpfs and hugetlbfs, it's most certainly worth to achieve it but in a later incremental patch. v3: Add hooking point for THP wrprotect faults. CC: Shaohua Li Signed-off-by: Andrea Arcangeli Signed-off-by: Peter Xu --- mm/memory.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff --git a/mm/memory.c b/mm/memory.c index e11ca9dd823f..00781c43407b 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -2483,6 +2483,11 @@ static vm_fault_t do_wp_page(struct vm_fault *vmf) { struct vm_area_struct *vma = vmf->vma; + if (userfaultfd_wp(vma)) { + pte_unmap_unlock(vmf->pte, vmf->ptl); + return handle_userfault(vmf, VM_UFFD_WP); + } + vmf->page = vm_normal_page(vma, vmf->address, vmf->orig_pte); if (!vmf->page) { /* @@ -2800,6 +2805,8 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) inc_mm_counter_fast(vma->vm_mm, MM_ANONPAGES); dec_mm_counter_fast(vma->vm_mm, MM_SWAPENTS); pte = mk_pte(page, vma->vm_page_prot); + if (userfaultfd_wp(vma)) + vmf->flags &= ~FAULT_FLAG_WRITE; if ((vmf->flags & FAULT_FLAG_WRITE) && reuse_swap_page(page, NULL)) { pte = maybe_mkwrite(pte_mkdirty(pte), vma); vmf->flags &= ~FAULT_FLAG_WRITE; @@ -3684,8 +3691,11 @@ static inline vm_fault_t create_huge_pmd(struct vm_fault *vmf) /* `inline' is required to avoid gcc 4.1.2 build error */ static inline vm_fault_t wp_huge_pmd(struct vm_fault *vmf, pmd_t orig_pmd) { - if (vma_is_anonymous(vmf->vma)) + if (vma_is_anonymous(vmf->vma)) { + if (userfaultfd_wp(vmf->vma)) + return handle_userfault(vmf, VM_UFFD_WP); return do_huge_pmd_wp_page(vmf, orig_pmd); + } if (vmf->vma->vm_ops->huge_fault) return vmf->vma->vm_ops->huge_fault(vmf, PE_SIZE_PMD); -- 2.17.1