From patchwork Mon Nov 15 07:55:05 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Peter Xu X-Patchwork-Id: 12618853 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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8FC8DC433EF for ; Mon, 15 Nov 2021 07:56:29 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 4157F63219 for ; Mon, 15 Nov 2021 07:56:29 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 4157F63219 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvack.org Received: by kanga.kvack.org (Postfix) id E07176B0087; Mon, 15 Nov 2021 02:56:28 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id D91066B0088; Mon, 15 Nov 2021 02:56:28 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id C0A7B6B0089; Mon, 15 Nov 2021 02:56:28 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0207.hostedemail.com [216.40.44.207]) by kanga.kvack.org (Postfix) with ESMTP id AA0F96B0087 for ; Mon, 15 Nov 2021 02:56:28 -0500 (EST) Received: from smtpin31.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 51F5E8249980 for ; Mon, 15 Nov 2021 07:56:28 +0000 (UTC) X-FDA: 78810407256.31.A26756E Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by imf19.hostedemail.com (Postfix) with ESMTP id BD207B0000BD for ; Mon, 15 Nov 2021 07:56:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1636962987; 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=PQTAYR2U0B9NQT5q5Dh9pQHL0/MM7Qz5TQPJEv+v98g=; b=VqdSPyr1TMRw5Sc1JaPh/CnbsFI90vx9l4gVJdaMgMnhZfZuKYauHz4MDJ+4s4YS97M8DS C9IqJzVs1i2J8FdB6U70AC2qXOwrdtkC2lG/0MdN7GM0YBP4YsMoFF4ZjVTBUt9Vn2TxVP SZfjUjdbjZt0iwgoqcYpfNMFIrFm6gY= Received: from mail-pf1-f199.google.com (mail-pf1-f199.google.com [209.85.210.199]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-398-0UCfQBLIN8ajQlpNf7ednA-1; Mon, 15 Nov 2021 02:56:26 -0500 X-MC-Unique: 0UCfQBLIN8ajQlpNf7ednA-1 Received: by mail-pf1-f199.google.com with SMTP id x14-20020a627c0e000000b0049473df362dso9577118pfc.12 for ; Sun, 14 Nov 2021 23:56:26 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=PQTAYR2U0B9NQT5q5Dh9pQHL0/MM7Qz5TQPJEv+v98g=; b=iURiSCGg43EhRVaL4u/OA8us7bbqsf5YOz+1YqJJuCNUfOnf6RmMUO2eidDNitBXDV huhw6n+xLC3dKz4/Jg51PKaLaJ51JEO1VEHFZiwLx92qESKeZAXD+o3YieBZxkfTSFdX hS49++HrXjg04EAemAcjIe34QUfiVXXSojBcYR/2fJP9QGf4j1wSg+EUlIaqfrh50BHa qg03Xi6PVt0UYHqvTwn4o5fgzd6unxQNtvcnmD7ultCKBtdu6Ln2VaUCJ3sukqc3mnyG jFEYK6RxP/Jcsnl3XS2sZjddNaR9vMjUhxQtYaMs2drc3F1eiuQCptCCtfJzJtjsiGSn hRSg== X-Gm-Message-State: AOAM533RatoJDSKYeWbDkpqkUsuUJa9v3tgBJNFej2HNKhR0wJmOXb5S RyxwFoFsq/igkCj+3WAf8QNTv7oMcXHoZTgVN5grKOyRlFyolNxS48MSA11H8U56koV+GyItNuL POljM1Tyr/CrRVPULgV8BdyuJ1F6UeWnhs3HOO3UY3MM7oMlL7gPCovxz8Ivz X-Received: by 2002:a17:90a:ca81:: with SMTP id y1mr61191372pjt.231.1636962984639; Sun, 14 Nov 2021 23:56:24 -0800 (PST) X-Google-Smtp-Source: ABdhPJwQVZcj01aFlbyqYO4BSw1DS5ur5lPKwB1eRxjFMR30tJL7G2a+EjobAshXx0ZYvcchxwbzZQ== X-Received: by 2002:a17:90a:ca81:: with SMTP id y1mr61191302pjt.231.1636962984128; Sun, 14 Nov 2021 23:56:24 -0800 (PST) Received: from localhost.localdomain ([191.101.132.223]) by smtp.gmail.com with ESMTPSA id e10sm15792796pfv.140.2021.11.14.23.56.16 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Sun, 14 Nov 2021 23:56:23 -0800 (PST) From: Peter Xu To: linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Axel Rasmussen , Nadav Amit , Mike Rapoport , Hugh Dickins , Mike Kravetz , "Kirill A . Shutemov" , Alistair Popple , Jerome Glisse , Matthew Wilcox , Andrew Morton , peterx@redhat.com, David Hildenbrand , Andrea Arcangeli Subject: [PATCH v6 06/23] mm/shmem: Handle uffd-wp special pte in page fault handler Date: Mon, 15 Nov 2021 15:55:05 +0800 Message-Id: <20211115075522.73795-7-peterx@redhat.com> X-Mailer: git-send-email 2.32.0 In-Reply-To: <20211115075522.73795-1-peterx@redhat.com> References: <20211115075522.73795-1-peterx@redhat.com> MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Authentication-Results: imf19.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=VqdSPyr1; spf=none (imf19.hostedemail.com: domain of peterx@redhat.com has no SPF policy when checking 170.10.133.124) smtp.mailfrom=peterx@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: BD207B0000BD X-Stat-Signature: pq1qrw74zcg4pdryg9fxy88t5hgsusix X-HE-Tag: 1636962977-367084 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: File-backed memories are prone to unmap/swap so the ptes are always unstable, because they can be easily faulted back later using the page cache. This could lead to uffd-wp getting lost when unmapping or swapping out such memory. One example is shmem. PTE markers are needed to store those information. This patch prepares it by handling uffd-wp pte markers first it is applied elsewhere, so that the page fault handler can recognize uffd-wp pte markers. The handling of uffd-wp pte markers is similar to missing fault, it's just that we'll handle this "missing fault" when we see the pte markers, meanwhile we need to make sure the marker information is kept during processing the fault. This is a slow path of uffd-wp handling, because zapping of wr-protected shmem ptes should be rare. So far it should only trigger in two conditions: (1) When trying to punch holes in shmem_fallocate(), there is an optimization to zap the pgtables before evicting the page. (2) When swapping out shmem pages. Because of this, the page fault handling is simplifed too by not sending the wr-protect message in the 1st page fault, instead the page will be installed read-only, so the uffd-wp message will be generated in the next fault, which will trigger the do_wp_page() path of general uffd-wp handling. Disable fault-around for all uffd-wp registered ranges for extra safety just like uffd-minor fault, and clean the code up. Signed-off-by: Peter Xu --- include/linux/userfaultfd_k.h | 17 +++++++++ mm/memory.c | 71 ++++++++++++++++++++++++++++++----- 2 files changed, 79 insertions(+), 9 deletions(-) diff --git a/include/linux/userfaultfd_k.h b/include/linux/userfaultfd_k.h index 7d7ffec53ddb..05cec02140cb 100644 --- a/include/linux/userfaultfd_k.h +++ b/include/linux/userfaultfd_k.h @@ -96,6 +96,18 @@ static inline bool uffd_disable_huge_pmd_share(struct vm_area_struct *vma) return vma->vm_flags & (VM_UFFD_WP | VM_UFFD_MINOR); } +/* + * Don't do fault around for either WP or MINOR registered uffd range. For + * MINOR registered range, fault around will be a total disaster and ptes can + * be installed without notifications; for WP it should mostly be fine as long + * as the fault around checks for pte_none() before the installation, however + * to be super safe we just forbid it. + */ +static inline bool uffd_disable_fault_around(struct vm_area_struct *vma) +{ + return vma->vm_flags & (VM_UFFD_WP | VM_UFFD_MINOR); +} + static inline bool userfaultfd_missing(struct vm_area_struct *vma) { return vma->vm_flags & VM_UFFD_MISSING; @@ -236,6 +248,11 @@ static inline void userfaultfd_unmap_complete(struct mm_struct *mm, { } +static inline bool uffd_disable_fault_around(struct vm_area_struct *vma) +{ + return false; +} + #endif /* CONFIG_USERFAULTFD */ static inline bool is_pte_marker_uffd_wp(pte_t pte) diff --git a/mm/memory.c b/mm/memory.c index d5966d9e24c3..e8557d43a87d 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -3452,6 +3452,43 @@ static vm_fault_t remove_device_exclusive_entry(struct vm_fault *vmf) return 0; } +static vm_fault_t pte_marker_clear(struct vm_fault *vmf) +{ + vmf->pte = pte_offset_map_lock(vmf->vma->vm_mm, vmf->pmd, + vmf->address, &vmf->ptl); + /* + * Be careful so that we will only recover a special uffd-wp pte into a + * none pte. Otherwise it means the pte could have changed, so retry. + */ + if (is_pte_marker(*vmf->pte)) + pte_clear(vmf->vma->vm_mm, vmf->address, vmf->pte); + pte_unmap_unlock(vmf->pte, vmf->ptl); + return 0; +} + +/* + * This is actually a page-missing access, but with uffd-wp special pte + * installed. It means this pte was wr-protected before being unmapped. + */ +static vm_fault_t pte_marker_handle_uffd_wp(struct vm_fault *vmf) +{ + /* Careful! vmf->pte unmapped after return */ + if (!pte_unmap_same(vmf)) + return 0; + + /* + * Just in case there're leftover special ptes even after the region + * got unregistered - we can simply clear them. We can also do that + * proactively when e.g. when we do UFFDIO_UNREGISTER upon some uffd-wp + * ranges, but it should be more efficient to be done lazily here. + */ + if (unlikely(!userfaultfd_wp(vmf->vma) || vma_is_anonymous(vmf->vma))) + return pte_marker_clear(vmf); + + /* do_fault() can handle pte markers too like none pte */ + return do_fault(vmf); +} + static vm_fault_t handle_pte_marker(struct vm_fault *vmf) { swp_entry_t entry = pte_to_swp_entry(vmf->orig_pte); @@ -3465,8 +3502,11 @@ static vm_fault_t handle_pte_marker(struct vm_fault *vmf) if (WARN_ON_ONCE(vma_is_anonymous(vmf->vma) || !marker)) return VM_FAULT_SIGBUS; - /* TODO: handle pte markers */ - return 0; + if (marker & PTE_MARKER_UFFD_WP) + return pte_marker_handle_uffd_wp(vmf); + + /* This is an unknown pte marker */ + return VM_FAULT_SIGBUS; } /* @@ -3968,6 +4008,7 @@ vm_fault_t do_set_pmd(struct vm_fault *vmf, struct page *page) void do_set_pte(struct vm_fault *vmf, struct page *page, unsigned long addr) { struct vm_area_struct *vma = vmf->vma; + bool uffd_wp = is_pte_marker_uffd_wp(vmf->orig_pte); bool write = vmf->flags & FAULT_FLAG_WRITE; bool prefault = vmf->address != addr; pte_t entry; @@ -3982,6 +4023,8 @@ void do_set_pte(struct vm_fault *vmf, struct page *page, unsigned long addr) if (write) entry = maybe_mkwrite(pte_mkdirty(entry), vma); + if (unlikely(uffd_wp)) + entry = pte_mkuffd_wp(pte_wrprotect(entry)); /* copy-on-write page */ if (write && !(vma->vm_flags & VM_SHARED)) { inc_mm_counter_fast(vma->vm_mm, MM_ANONPAGES); @@ -4155,9 +4198,21 @@ static vm_fault_t do_fault_around(struct vm_fault *vmf) return vmf->vma->vm_ops->map_pages(vmf, start_pgoff, end_pgoff); } +/* Return true if we should do read fault-around, false otherwise */ +static inline bool should_fault_around(struct vm_fault *vmf) +{ + /* No ->map_pages? No way to fault around... */ + if (!vmf->vma->vm_ops->map_pages) + return false; + + if (uffd_disable_fault_around(vmf->vma)) + return false; + + return fault_around_bytes >> PAGE_SHIFT > 1; +} + static vm_fault_t do_read_fault(struct vm_fault *vmf) { - struct vm_area_struct *vma = vmf->vma; vm_fault_t ret = 0; /* @@ -4165,12 +4220,10 @@ static vm_fault_t do_read_fault(struct vm_fault *vmf) * if page by the offset is not ready to be mapped (cold cache or * something). */ - if (vma->vm_ops->map_pages && fault_around_bytes >> PAGE_SHIFT > 1) { - if (likely(!userfaultfd_minor(vmf->vma))) { - ret = do_fault_around(vmf); - if (ret) - return ret; - } + if (should_fault_around(vmf)) { + ret = do_fault_around(vmf); + if (ret) + return ret; } ret = __do_fault(vmf);