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 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9E9F1C4332F for ; Sat, 24 Dec 2022 16:59:55 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 06DCB940010; Sat, 24 Dec 2022 11:59:55 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 01D6094000A; Sat, 24 Dec 2022 11:59:54 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id E0003940010; Sat, 24 Dec 2022 11:59:54 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id CE5E394000A for ; Sat, 24 Dec 2022 11:59:54 -0500 (EST) Received: from smtpin27.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id 7EEC01406C1 for ; Sat, 24 Dec 2022 16:59:54 +0000 (UTC) X-FDA: 80277811908.27.9F091A2 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by imf13.hostedemail.com (Postfix) with ESMTP id D689720011 for ; Sat, 24 Dec 2022 16:59:51 +0000 (UTC) Authentication-Results: imf13.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=d1vRuQpG; dmarc=pass (policy=none) header.from=redhat.com; spf=pass (imf13.hostedemail.com: domain of david@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=david@redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1671901192; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=Zi9z1mc5tct2OqLs3x0XC3e3royxe6qT3uotyRD/VDI=; b=6eMnsPEisZLQy+yqApNK4gLoQQfO1UeGpymj6+0WvjcI9KBjuuMytwc8oQhf+JpKzaDEBY ReW12ibYv1Nlid7mF9/plhnCMhFyHN/XQ6MgzE+euAQ8cwUzB6X3QcSLdYboUr9KPHV/fP 3mt2rttUPpsbb4925jlfkr6T4VAPHMg= ARC-Authentication-Results: i=1; imf13.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=d1vRuQpG; dmarc=pass (policy=none) header.from=redhat.com; spf=pass (imf13.hostedemail.com: domain of david@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=david@redhat.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1671901192; a=rsa-sha256; cv=none; b=lSoPHeBeFi7PXoDFp3g3m8wN/6lJ3U5hZV4UGfvoOLi6LY28/Jq0hbl72KX7CdXbaTF0Cs Jx8dMMTuTzeB6AABUfKCMiwdJ7h9+UimzlhCOHLmlxb7+sJ+H8XXhN3Vwv76AoQqivsOuj 5R3JS727wq45uyku9RPbY+2+5vMU0/E= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1671901191; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Zi9z1mc5tct2OqLs3x0XC3e3royxe6qT3uotyRD/VDI=; b=d1vRuQpG4htN1432hlk4bN3eDNi9JBodZwrh9yh6NJK1BKbLaeZhNm9dY6LGEsK4owv5xM vgPFz3YLF0KWEzFnB1wwMXEBaY+3WYQeAVRnPffGSI4kEYohteWppuuDpL/NS/rQQ1t25g 9f19yJgUFvgwPms18U75rvJ68WJ6YVg= Received: from mail-wm1-f69.google.com (mail-wm1-f69.google.com [209.85.128.69]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_128_GCM_SHA256) id us-mta-638-z3MBHCIuND22l9awFIRG2Q-1; Sat, 24 Dec 2022 11:59:49 -0500 X-MC-Unique: z3MBHCIuND22l9awFIRG2Q-1 Received: by mail-wm1-f69.google.com with SMTP id bi19-20020a05600c3d9300b003cf9d6c4016so5509478wmb.8 for ; Sat, 24 Dec 2022 08:59:49 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:in-reply-to:organization:from :content-language:references:cc:to:subject:user-agent:mime-version :date:message-id:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=Zi9z1mc5tct2OqLs3x0XC3e3royxe6qT3uotyRD/VDI=; b=5MQ8H1hfAyUXBplrKTa1NeEC4d/L8TLpzbFCxAZt7hP1WHV6QyMz9BgV+PofdEvW86 gOXm7ocKfljJAjUKa4mNHmULwOiX42F2vNqrUtPflieakhKvFku46+Tchx4cmZs4VPZC z2tfa8yCUYgEKfz1g8Z0ezfCt62AoSdxiqYXXET3CtLtN9i1kuR3C2mzIi52iMBp1MZI bSJOMcyhBEeI2E4H2WN7k7Bn+Pi2ZwizdWl06UXb7gUcN2rVGIT/MmBuIUm7w9zvv0wg 59EZu4psiDuIsjyPRgBF9IB2kDl13wGwXSzevkQ3BqZzMAO2+QhvpTRlQAcz5Qd+QZwd kg+Q== X-Gm-Message-State: AFqh2kqNltxu3aQzTN/8Y1MS0wQUPFeg+b8PjSf/94AHT27Z7nlbB4xV NUZyYfYkOSzdJ9qeZHf0vnO0FunE2J0hNHgNaPb21HqF9bo52++3pLLG7EvQqLMK8dRPPV1seoc qZS5jp006Q0U= X-Received: by 2002:a05:600c:34d3:b0:3c6:e61e:ae74 with SMTP id d19-20020a05600c34d300b003c6e61eae74mr11675830wmq.4.1671901188784; Sat, 24 Dec 2022 08:59:48 -0800 (PST) X-Google-Smtp-Source: AMrXdXtDOuWW0o5NMKEEoENCst0sHVaIxFgrtRrGiP7J3uJ4XL6zV86Juaiob1DDiIFd9D6T2mG2ZA== X-Received: by 2002:a05:600c:34d3:b0:3c6:e61e:ae74 with SMTP id d19-20020a05600c34d300b003c6e61eae74mr11675815wmq.4.1671901188517; Sat, 24 Dec 2022 08:59:48 -0800 (PST) Received: from ?IPV6:2003:d8:2f16:1800:a9b4:1776:c5d9:1d9a? (p200300d82f161800a9b41776c5d91d9a.dip0.t-ipconnect.de. [2003:d8:2f16:1800:a9b4:1776:c5d9:1d9a]) by smtp.gmail.com with ESMTPSA id j20-20020a05600c191400b003b4fe03c881sm14564744wmq.48.2022.12.24.08.59.47 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 24 Dec 2022 08:59:48 -0800 (PST) Message-ID: <71412742-a71f-9c74-865f-773ad83db7a5@redhat.com> Date: Sat, 24 Dec 2022 17:59:45 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.6.0 Subject: Re: [PATCH v1 1/2] mm/userfaultfd: rely on vma->vm_page_prot in uffd_wp_range() To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, Andrew Morton , Peter Xu , Hugh Dickins , Andrea Arcangeli , Nadav Amit References: <20221223155616.297723-1-david@redhat.com> <20221223155616.297723-2-david@redhat.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: <20221223155616.297723-2-david@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: D689720011 X-Stat-Signature: 99erxqdnd579rcu1jbr5gdkgsxjnhtbo X-HE-Tag: 1671901191-369631 X-HE-Meta: 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 IuasM742 /kt+M9Q1Wqj4lfnJH6gU6Tyq0bg9nU12Z58JFdCyPKKrCqbbAUtt79M097+gbsDlOE5csrI+UcEm13DnMXK3bUK8nIs9dJ7+X+NZq49jk+AASMchVbEpmNfhdj0u+cec3orlKIHZpU7gUaNgkpqOxw28weQFTR8nlpCpqxj8vMUHxM2PV8pTfgSNaQTJGtsyjTcw86ls6ZtSWK5nynqPIlqTFRjO+Ap8quVVkuYlUkQ193b9LOqg7Z0QP5q7ng9dkcGxGRbVcGEYBNbo= 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: On 23.12.22 16:56, David Hildenbrand wrote: > uffd_wp_range() currently calculates page protection manually using > vm_get_page_prot(). This will ignore any other reason for active > writenotify: one mechanism applicable to shmem is softdirty tracking. > > For example, the following sequence > > 1) Write to mapped shmem page > 2) Clear softdirty > 3) Register uffd-wp covering the mapped page > 4) Unregister uffd-wp covering the mapped page > 5) Write to page again > > will not set the modified page softdirty, because uffd_wp_range() will > ignore that writenotify is required for softdirty tracking and simply map > the page writable again using change_protection(). Similarly, instead of > unregistering, protecting followed by un-protecting the page using > uffd-wp would result in the same situation. > > Now that we enable writenotify whenever enabling uffd-wp on a VMA, > vma->vm_page_prot will already properly reflect our requirements: the > default is to write-protect all PTEs. However, for shared mappings we > would now not remap the PTEs writable if possible when unprotecting, just > like for private mappings (COW). To compensate, set > MM_CP_TRY_CHANGE_WRITABLE just like mprotect() does to try mapping > individual PTEs writable. > > For private mappings, this change implies that we will now always try > setting PTEs writable when un-protecting, just like when upgrading write > permissions using mprotect(), which is an improvement. > > For shared mappings, we will only set PTEs writable if > can_change_pte_writable()/can_change_pmd_writable() indicates that it's > ok. For ordinary shmem, this will be the case when PTEs are dirty, which > should usually be the case -- otherwise we could special-case shmem in > can_change_pte_writable()/can_change_pmd_writable() easily, because > shmem itself doesn't require writenotify. > > Note that hugetlb does not yet implement MM_CP_TRY_CHANGE_WRITABLE, so we > won't try setting PTEs writable when unprotecting or when unregistering > uffd-wp. This can be added later on top by implementing > MM_CP_TRY_CHANGE_WRITABLE. > > While commit ffd05793963a ("userfaultfd: wp: support write protection for > userfault vma range") introduced that code, it should only be applicable > to uffd-wp on shared mappings -- shmem (hugetlb does not support softdirty > tracking). I don't think this corner cases justifies to cc stable. Let's > just handle it correctly and prepare for change_protection() cleanups. > > Fixes: b1f9e876862d ("mm/uffd: enable write protection for shmem & hugetlbfs") > Signed-off-by: David Hildenbrand > --- > mm/userfaultfd.c | 18 +++++++++++++----- > 1 file changed, 13 insertions(+), 5 deletions(-) > > diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c > index 0499907b6f1a..351e8d6b398b 100644 > --- a/mm/userfaultfd.c > +++ b/mm/userfaultfd.c > @@ -727,17 +727,25 @@ ssize_t mcopy_continue(struct mm_struct *dst_mm, unsigned long start, > void uffd_wp_range(struct mm_struct *dst_mm, struct vm_area_struct *dst_vma, > unsigned long start, unsigned long len, bool enable_wp) > { > + unsigned int mm_cp_flags; > struct mmu_gather tlb; > - pgprot_t newprot; > > if (enable_wp) > - newprot = vm_get_page_prot(dst_vma->vm_flags & ~(VM_WRITE)); > + mm_cp_flags = MM_CP_UFFD_WP; > else > - newprot = vm_get_page_prot(dst_vma->vm_flags); > + mm_cp_flags = MM_CP_UFFD_WP_RESOLVE; > > + /* > + * vma->vm_page_prot already reflects that uffd-wp is enabled for this > + * VMA (see userfaultfd_set_vm_flags()) and that all PTEs are supposed > + * to be write-protected as default whenever protection changes. > + * Try upgrading write permissions manually. > + */ > + if (vma_wants_manual_pte_write_upgrade(dst_vma)) > + mm_cp_flags |= MM_CP_TRY_CHANGE_WRITABLE; > tlb_gather_mmu(&tlb, dst_mm); > - change_protection(&tlb, dst_vma, start, start + len, newprot, > - enable_wp ? MM_CP_UFFD_WP : MM_CP_UFFD_WP_RESOLVE); > + change_protection(&tlb, dst_vma, start, start + len, vma->vm_page_prot, > + mm_cp_flags); > tlb_finish_mmu(&tlb); > } > The following optimization makes sense: From 779b36768328d99dbcc96fbba7be8b50536ce350 Mon Sep 17 00:00:00 2001 From: David Hildenbrand Date: Sat, 24 Dec 2022 15:02:36 +0100 Subject: [PATCH] fixup: mm/userfaultfd: enable writenotify while userfaultfd-wp is enabled for a VMA No need for additional harmless checks if we're wr-protecting either way. Signed-off-by: David Hildenbrand --- mm/userfaultfd.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index be7ee9d82e72..1ac1de527719 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -741,7 +741,7 @@ void uffd_wp_range(struct mm_struct *dst_mm, struct vm_area_struct *dst_vma, * to be write-protected as default whenever protection changes. * Try upgrading write permissions manually. */ - if (vma_wants_manual_pte_write_upgrade(dst_vma)) + if (!enable_wp && vma_wants_manual_pte_write_upgrade(dst_vma)) mm_cp_flags |= MM_CP_TRY_CHANGE_WRITABLE; tlb_gather_mmu(&tlb, dst_mm); change_protection(&tlb, dst_vma, start, start + len, mm_cp_flags); -- 2.38.1 -- Thanks, David / dhildenb