From patchwork Thu Jul 15 20:14:00 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Peter Xu X-Patchwork-Id: 12380929 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=-16.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT 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 29251C636C9 for ; Thu, 15 Jul 2021 20:14:38 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id D23BA60FF3 for ; Thu, 15 Jul 2021 20:14:37 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D23BA60FF3 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 412A88D0100; Thu, 15 Jul 2021 16:14:38 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 3EB138D00EC; Thu, 15 Jul 2021 16:14:38 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 23BCB8D0100; Thu, 15 Jul 2021 16:14:38 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0220.hostedemail.com [216.40.44.220]) by kanga.kvack.org (Postfix) with ESMTP id 032028D00EC for ; Thu, 15 Jul 2021 16:14:37 -0400 (EDT) Received: from smtpin29.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id DD4A026DF6 for ; Thu, 15 Jul 2021 20:14:36 +0000 (UTC) X-FDA: 78365924952.29.02A90F3 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [216.205.24.124]) by imf05.hostedemail.com (Postfix) with ESMTP id 77E45500FC1D for ; Thu, 15 Jul 2021 20:14:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1626380075; 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=Y0JmFuDDelZXYWv/E+BZRvjlS5kkw3E6CXCgFUA2NEY=; b=Ji8Ryf+96mtraHmRh/2FvOi4Z6CyXGSZMsCbMM8G5JKBr9PVzNotDnIi2qg3/vMALu0/zN 1OYWsnU4yeYFSsic8quyy46P/3VsnvnzqQBWCj2reMxHpl3edDMlHr9kJktFIzUESKhPJm qnVa8iCw/C239KkQTTZEULDeZzfI6x4= Received: from mail-qv1-f72.google.com (mail-qv1-f72.google.com [209.85.219.72]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-281-1o0g6CMBOdKGpXXwizbEPg-1; Thu, 15 Jul 2021 16:14:34 -0400 X-MC-Unique: 1o0g6CMBOdKGpXXwizbEPg-1 Received: by mail-qv1-f72.google.com with SMTP id z1-20020a0cfec10000b02902dbb4e0a8f2so5028972qvs.6 for ; Thu, 15 Jul 2021 13:14:34 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=Y0JmFuDDelZXYWv/E+BZRvjlS5kkw3E6CXCgFUA2NEY=; b=pA4jw7q7EB97pbAMswLz5ELYyUSDvC0SGtFvCGk+qt9rLFocnqy9nNpfT1BAKZcirk Jivlz0Rfkwfqf1hVMLjl4iLz/2YeJDzL0GfPfwksodmHbJPCEePG91nizSXqbXb3qp1o XsoHrguJGUpvhpgnhPU7kx0rsW5Q6IEBh9ywLS0srlxZTbj0/B8rEPIsm04iE/7Jt31y qzpF1m7Kh7pGUiR5ORKCcnV2+PS7KCq7VU3HSaZotDuoOFzVtwBdlyY5fHNyvK/RcSme MkcGrZwPjYyn/U1GhwOeRAqs2I+k2MZ1ozVf3i/E6HQCIOoTTEgz9RgoT11tWmaMqgTT LYVQ== X-Gm-Message-State: AOAM5336dRMgiqXg4OcWx3UB/R16ta4Wcsfrtzbee5zTVKxbstduA3ji qzcR6lze5ceUaV4uZnXm78EODRU5lDOGociomrUK0TayTC8X3eLC8FhfCjUI/rj+wK9qAhCN8kg SjWKxiABZ2ah0CqJv4J2g+34g9lkryZ/WdMpFYe4s9lPEWkSxmGSUDtypZ410 X-Received: by 2002:a05:6214:5b0:: with SMTP id by16mr6034953qvb.54.1626380073849; Thu, 15 Jul 2021 13:14:33 -0700 (PDT) X-Google-Smtp-Source: ABdhPJw7fWzr5P/wUOBCBzeu3pvVNU1EGhe2aUz3WLeAyZKgAp4DMoDdS0/Ut3Qq5Y4kozsnzR0Qaw== X-Received: by 2002:a05:6214:5b0:: with SMTP id by16mr6034912qvb.54.1626380073524; Thu, 15 Jul 2021 13:14:33 -0700 (PDT) Received: from localhost.localdomain (bras-base-toroon474qw-grc-65-184-144-111-238.dsl.bell.ca. [184.144.111.238]) by smtp.gmail.com with ESMTPSA id p64sm2915206qka.114.2021.07.15.13.14.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 15 Jul 2021 13:14:33 -0700 (PDT) From: Peter Xu To: linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Jason Gunthorpe , Mike Kravetz , David Hildenbrand , Alistair Popple , Matthew Wilcox , "Kirill A . Shutemov" , Hugh Dickins , Tiberiu Georgescu , Andrea Arcangeli , Axel Rasmussen , Nadav Amit , Mike Rapoport , Jerome Glisse , Andrew Morton , Miaohe Lin , peterx@redhat.com Subject: [PATCH v5 04/26] mm/userfaultfd: Introduce special pte for unmapped file-backed mem Date: Thu, 15 Jul 2021 16:14:00 -0400 Message-Id: <20210715201422.211004-5-peterx@redhat.com> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20210715201422.211004-1-peterx@redhat.com> References: <20210715201422.211004-1-peterx@redhat.com> MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Authentication-Results: imf05.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=Ji8Ryf+9; spf=none (imf05.hostedemail.com: domain of peterx@redhat.com has no SPF policy when checking 216.205.24.124) smtp.mailfrom=peterx@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-Rspamd-Server: rspam05 X-Stat-Signature: 14d54xcbnsfp9jnnuug75z6hp7jeyq7w X-Rspamd-Queue-Id: 77E45500FC1D X-HE-Tag: 1626380076-937214 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: This patch introduces a very special swap-like pte for file-backed memories. Currently it's only defined for x86_64 only, but as long as any arch that can properly define the UFFD_WP_SWP_PTE_SPECIAL value as requested, it should conceptually work too. We will use this special pte to arm the ptes that got either unmapped or swapped out for a file-backed region that was previously wr-protected. This special pte could trigger a page fault just like swap entries, and as long as the page fault will satisfy pte_none()==false && pte_present()==false. Then we can revive the special pte into a normal pte backed by the page cache. This idea is greatly inspired by Hugh and Andrea in the discussion, which is referenced in the links below. The other idea (from Hugh) is that we use swp_type==1 and swp_offset=0 as the special pte. The current solution (as pointed out by Andrea) is slightly preferred in that we don't even need swp_entry_t knowledge at all in trapping these accesses. Meanwhile, we also reuse _PAGE_SWP_UFFD_WP from the anonymous swp entries. This patch only introduces the special pte and its operators. It's not yet applied to have any functional difference. Link: https://lore.kernel.org/lkml/20201126222359.8120-1-peterx@redhat.com/ Link: https://lore.kernel.org/lkml/20201130230603.46187-1-peterx@redhat.com/ Suggested-by: Andrea Arcangeli Suggested-by: Hugh Dickins Signed-off-by: Peter Xu --- arch/x86/include/asm/pgtable.h | 28 ++++++++++++++++++++++++++++ include/asm-generic/pgtable_uffd.h | 3 +++ include/linux/userfaultfd_k.h | 25 +++++++++++++++++++++++++ 3 files changed, 56 insertions(+) diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h index 448cd01eb3ec..71b1e73d5b26 100644 --- a/arch/x86/include/asm/pgtable.h +++ b/arch/x86/include/asm/pgtable.h @@ -1300,6 +1300,34 @@ static inline pmd_t pmd_swp_clear_soft_dirty(pmd_t pmd) #endif #ifdef CONFIG_HAVE_ARCH_USERFAULTFD_WP + +/* + * This is a very special swap-like pte that marks this pte as "wr-protected" + * by userfaultfd-wp. It should only exist for file-backed memory where the + * page (previously got wr-protected) has been unmapped or swapped out. + * + * For anonymous memories, the userfaultfd-wp _PAGE_SWP_UFFD_WP bit is kept + * along with a real swp entry instead. + * + * Let's make some rules for this special pte: + * + * (1) pte_none()==false, so that it'll not trigger a missing page fault. + * + * (2) pte_present()==false, so that it's recognized as swap (is_swap_pte). + * + * (3) pte_swp_uffd_wp()==true, so it can be tested just like a swap pte that + * contains a valid swap entry, so that we can check a swap pte always + * using "is_swap_pte() && pte_swp_uffd_wp()" without caring about whether + * there's one swap entry inside of the pte. + * + * (4) It should not be a valid swap pte anywhere, so that when we see this pte + * we know it does not contain a swap entry. + * + * For x86, the simplest special pte which satisfies all of above should be the + * pte with only _PAGE_SWP_UFFD_WP bit set (where swp_type==swp_offset==0). + */ +#define UFFD_WP_SWP_PTE_SPECIAL __pte(_PAGE_SWP_UFFD_WP) + static inline pte_t pte_swp_mkuffd_wp(pte_t pte) { return pte_set_flags(pte, _PAGE_SWP_UFFD_WP); diff --git a/include/asm-generic/pgtable_uffd.h b/include/asm-generic/pgtable_uffd.h index 828966d4c281..95e9811ce9d1 100644 --- a/include/asm-generic/pgtable_uffd.h +++ b/include/asm-generic/pgtable_uffd.h @@ -2,6 +2,9 @@ #define _ASM_GENERIC_PGTABLE_UFFD_H #ifndef CONFIG_HAVE_ARCH_USERFAULTFD_WP + +#define UFFD_WP_SWP_PTE_SPECIAL __pte(0) + static __always_inline int pte_uffd_wp(pte_t pte) { return 0; diff --git a/include/linux/userfaultfd_k.h b/include/linux/userfaultfd_k.h index 331d2ccf0bcc..bb5a72a2b07a 100644 --- a/include/linux/userfaultfd_k.h +++ b/include/linux/userfaultfd_k.h @@ -145,6 +145,21 @@ extern int userfaultfd_unmap_prep(struct vm_area_struct *vma, extern void userfaultfd_unmap_complete(struct mm_struct *mm, struct list_head *uf); +static inline pte_t pte_swp_mkuffd_wp_special(struct vm_area_struct *vma) +{ + WARN_ON_ONCE(vma_is_anonymous(vma)); + return UFFD_WP_SWP_PTE_SPECIAL; +} + +static inline bool pte_swp_uffd_wp_special(pte_t pte) +{ +#ifdef CONFIG_HAVE_ARCH_USERFAULTFD_WP + return pte_same(pte, UFFD_WP_SWP_PTE_SPECIAL); +#else + return false; +#endif +} + #else /* CONFIG_USERFAULTFD */ /* mm helpers */ @@ -234,6 +249,16 @@ static inline void userfaultfd_unmap_complete(struct mm_struct *mm, { } +static inline pte_t pte_swp_mkuffd_wp_special(struct vm_area_struct *vma) +{ + return __pte(0); +} + +static inline bool pte_swp_uffd_wp_special(pte_t pte) +{ + return false; +} + #endif /* CONFIG_USERFAULTFD */ #endif /* _LINUX_USERFAULTFD_K_H */