From patchwork Tue Apr 20 22:07:57 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Axel Rasmussen X-Patchwork-Id: 12215093 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=-26.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT,USER_IN_DEF_DKIM_WL autolearn=unavailable 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 B4F06C43461 for ; Tue, 20 Apr 2021 22:08:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8895861405 for ; Tue, 20 Apr 2021 22:08:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234302AbhDTWIz (ORCPT ); Tue, 20 Apr 2021 18:08:55 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40322 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234253AbhDTWIs (ORCPT ); Tue, 20 Apr 2021 18:08:48 -0400 Received: from mail-yb1-xb49.google.com (mail-yb1-xb49.google.com [IPv6:2607:f8b0:4864:20::b49]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 074F3C06138D for ; Tue, 20 Apr 2021 15:08:15 -0700 (PDT) Received: by mail-yb1-xb49.google.com with SMTP id k5-20020a2524050000b02904e716d0d7b1so13313647ybk.0 for ; Tue, 20 Apr 2021 15:08:14 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:in-reply-to:message-id:mime-version:references:subject:from:to :cc; bh=DQGQsByibd5yN2vyWTzTceXotmY0k6aoP/1N2N9IuiE=; b=u0L5Qq+KFD/DUNNDpJAJwZr3GYahHPsiA5cWRr+EbF2YkjZGVqFSUnUHu0jIwIm94I dCg+THjA2ozjBNbbJlIR1Q7JLlgkTLKSSDy4z2Y4Fo+HATHTnQmqRKDPZHo/EOc5SEo6 8mtK9EnySkHZ69l42kwrWFe6KqSj0JKSA+bZQTdtEeg7Dm25TvFWAaLfb2CB7998pKvH QEezt0j8RxhGlm9Vvqx4R7kOX/j0zIaWxGFQ1fhGLMcA7BYaGiZ0dnawFv2y4o/NUEtb MdYVjiIBDvZyzhTJnuhKcomLm5lB8kMhiBKHMzZfm0/01OtZOW8eqd6zYsjU2js3uNx2 d8JQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc; bh=DQGQsByibd5yN2vyWTzTceXotmY0k6aoP/1N2N9IuiE=; b=PsPqhDwdFcSZ8Mk/KfFRBafJaF/lUpcD7hQ3mRla9H0wZErdA95Kv3Escat7TM5WGs RTpUkHslCIiQgYQUxt3QVKB2HHxqpXB22+rETVu7kh/PfxdZYN+wKo/Tzzgf0q5LwH/t xH+JzudoQcWi5qIjIA9je7d4Fc7IN0sU0tNdLhMKeqef2Lg4u6nU3xDbRKYUWKs7+x02 e8zlooYti4YmpAZcwUl0NQFIGMEB5r3gRD42GQkyczyAu1TxBGPq4OnINV4E3l6SnJQZ sRl+SE16Uzjahx+VfsG0x5BKCwEj65U32Or6IKiZY8FfZjSu5KkBO2eA8KC2pa6Ig9qw 6Ciw== X-Gm-Message-State: AOAM530uPkXAA1jBLYTSEakecubhV543WhCJWWF59PfjrUxjcvsexi2I 5WL7J6l5+xSsp5BiVSatZTRZFq32ioJLS8jI5G6Z X-Google-Smtp-Source: ABdhPJym7CLvSXYY6OmrT0Ki+DwG8X3Vq/qx2Z8JcjPLcMOks3PzNmaXD7FSPq3/5s36n7xGPfGbhgTbHWygAEttU4M9 X-Received: from ajr0.svl.corp.google.com ([2620:15c:2cd:203:c40e:ee2c:2ab8:257a]) (user=axelrasmussen job=sendgmr) by 2002:a25:b78c:: with SMTP id n12mr28077499ybh.291.1618956494265; Tue, 20 Apr 2021 15:08:14 -0700 (PDT) Date: Tue, 20 Apr 2021 15:07:57 -0700 In-Reply-To: <20210420220804.486803-1-axelrasmussen@google.com> Message-Id: <20210420220804.486803-4-axelrasmussen@google.com> Mime-Version: 1.0 References: <20210420220804.486803-1-axelrasmussen@google.com> X-Mailer: git-send-email 2.31.1.368.gbe11c130af-goog Subject: [PATCH v4 03/10] userfaultfd/shmem: support UFFDIO_CONTINUE for shmem From: Axel Rasmussen To: Alexander Viro , Andrea Arcangeli , Andrew Morton , Hugh Dickins , Jerome Glisse , Joe Perches , Lokesh Gidra , Mike Kravetz , Mike Rapoport , Peter Xu , Shaohua Li , Shuah Khan , Stephen Rothwell , Wang Qing Cc: linux-api@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mm@kvack.org, Axel Rasmussen , Brian Geffon , "Dr . David Alan Gilbert" , Mina Almasry , Oliver Upton Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org With this change, userspace can resolve a minor fault within a shmem-backed area with a UFFDIO_CONTINUE ioctl. The semantics for this match those for hugetlbfs - we look up the existing page in the page cache, and install a PTE for it. This commit introduces a new helper: mcopy_atomic_install_pte. Why handle UFFDIO_CONTINUE for shmem in mm/userfaultfd.c, instead of in shmem.c? The existing userfault implementation only relies on shmem.c for VM_SHARED VMAs. However, minor fault handling / CONTINUE work just fine for !VM_SHARED VMAs as well. We'd prefer to handle CONTINUE for shmem in one place, regardless of shared/private (to reduce code duplication). Why add a new mcopy_atomic_install_pte helper? A problem we have with continue is that shmem_mcopy_atomic_pte() and mcopy_atomic_pte() are *close* to what we want, but not exactly. We do want to setup the PTEs in a CONTINUE operation, but we don't want to e.g. allocate a new page, charge it (e.g. to the shmem inode), manipulate various flags, etc. Also we have the problem stated above: shmem_mcopy_atomic_pte() and mcopy_atomic_pte() both handle one-half of the problem (shared / private) continue cares about. So, introduce mcontinue_atomic_pte(), to handle all of the shmem continue cases. Introduce the helper so it doesn't duplicate code with mcopy_atomic_pte(). In a future commit, shmem_mcopy_atomic_pte() will also be modified to use this new helper. However, since this is a bigger refactor, it seems most clear to do it as a separate change. Signed-off-by: Axel Rasmussen Acked-by: Hugh Dickins --- mm/userfaultfd.c | 172 ++++++++++++++++++++++++++++++++++------------- 1 file changed, 127 insertions(+), 45 deletions(-) diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index 23fa2583bbd1..51d8c0127161 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -48,6 +48,83 @@ struct vm_area_struct *find_dst_vma(struct mm_struct *dst_mm, return dst_vma; } +/* + * Install PTEs, to map dst_addr (within dst_vma) to page. + * + * This function handles MCOPY_ATOMIC_CONTINUE (which is always file-backed), + * whether or not dst_vma is VM_SHARED. It also handles the more general + * MCOPY_ATOMIC_NORMAL case, when dst_vma is *not* VM_SHARED (it may be file + * backed, or not). + * + * Note that MCOPY_ATOMIC_NORMAL for a VM_SHARED dst_vma is handled by + * shmem_mcopy_atomic_pte instead. + */ +static int mcopy_atomic_install_pte(struct mm_struct *dst_mm, pmd_t *dst_pmd, + struct vm_area_struct *dst_vma, + unsigned long dst_addr, struct page *page, + bool newly_allocated, bool wp_copy) +{ + int ret; + pte_t _dst_pte, *dst_pte; + bool writable = dst_vma->vm_flags & VM_WRITE; + bool vm_shared = dst_vma->vm_flags & VM_SHARED; + bool page_in_cache = page->mapping; + spinlock_t *ptl; + struct inode *inode; + pgoff_t offset, max_off; + + _dst_pte = mk_pte(page, dst_vma->vm_page_prot); + if (page_in_cache && !vm_shared) + writable = false; + if (writable || !page_in_cache) + _dst_pte = pte_mkdirty(_dst_pte); + if (writable) { + if (wp_copy) + _dst_pte = pte_mkuffd_wp(_dst_pte); + else + _dst_pte = pte_mkwrite(_dst_pte); + } + + dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl); + + if (vma_is_shmem(dst_vma)) { + /* serialize against truncate with the page table lock */ + inode = dst_vma->vm_file->f_inode; + offset = linear_page_index(dst_vma, dst_addr); + max_off = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE); + ret = -EFAULT; + if (unlikely(offset >= max_off)) + goto out_unlock; + } + + ret = -EEXIST; + if (!pte_none(*dst_pte)) + goto out_unlock; + + if (page_in_cache) + page_add_file_rmap(page, false); + else + page_add_new_anon_rmap(page, dst_vma, dst_addr, false); + + /* + * Must happen after rmap, as mm_counter() checks mapping (via + * PageAnon()), which is set by __page_set_anon_rmap(). + */ + inc_mm_counter(dst_mm, mm_counter(page)); + + if (newly_allocated) + lru_cache_add_inactive_or_unevictable(page, dst_vma); + + set_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte); + + /* No need to invalidate - it was non-present before */ + update_mmu_cache(dst_vma, dst_addr, dst_pte); + ret = 0; +out_unlock: + pte_unmap_unlock(dst_pte, ptl); + return ret; +} + static int mcopy_atomic_pte(struct mm_struct *dst_mm, pmd_t *dst_pmd, struct vm_area_struct *dst_vma, @@ -56,13 +133,9 @@ static int mcopy_atomic_pte(struct mm_struct *dst_mm, struct page **pagep, bool wp_copy) { - pte_t _dst_pte, *dst_pte; - spinlock_t *ptl; void *page_kaddr; int ret; struct page *page; - pgoff_t offset, max_off; - struct inode *inode; if (!*pagep) { ret = -ENOMEM; @@ -99,43 +172,12 @@ static int mcopy_atomic_pte(struct mm_struct *dst_mm, if (mem_cgroup_charge(page, dst_mm, GFP_KERNEL)) goto out_release; - _dst_pte = pte_mkdirty(mk_pte(page, dst_vma->vm_page_prot)); - if (dst_vma->vm_flags & VM_WRITE) { - if (wp_copy) - _dst_pte = pte_mkuffd_wp(_dst_pte); - else - _dst_pte = pte_mkwrite(_dst_pte); - } - - dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl); - if (dst_vma->vm_file) { - /* the shmem MAP_PRIVATE case requires checking the i_size */ - inode = dst_vma->vm_file->f_inode; - offset = linear_page_index(dst_vma, dst_addr); - max_off = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE); - ret = -EFAULT; - if (unlikely(offset >= max_off)) - goto out_release_uncharge_unlock; - } - ret = -EEXIST; - if (!pte_none(*dst_pte)) - goto out_release_uncharge_unlock; - - inc_mm_counter(dst_mm, MM_ANONPAGES); - page_add_new_anon_rmap(page, dst_vma, dst_addr, false); - lru_cache_add_inactive_or_unevictable(page, dst_vma); - - set_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte); - - /* No need to invalidate - it was non-present before */ - update_mmu_cache(dst_vma, dst_addr, dst_pte); - - pte_unmap_unlock(dst_pte, ptl); - ret = 0; + ret = mcopy_atomic_install_pte(dst_mm, dst_pmd, dst_vma, dst_addr, + page, true, wp_copy); + if (ret) + goto out_release; out: return ret; -out_release_uncharge_unlock: - pte_unmap_unlock(dst_pte, ptl); out_release: put_page(page); goto out; @@ -176,6 +218,41 @@ static int mfill_zeropage_pte(struct mm_struct *dst_mm, return ret; } +/* Handles UFFDIO_CONTINUE for all shmem VMAs (shared or private). */ +static int mcontinue_atomic_pte(struct mm_struct *dst_mm, + pmd_t *dst_pmd, + struct vm_area_struct *dst_vma, + unsigned long dst_addr, + bool wp_copy) +{ + struct inode *inode = file_inode(dst_vma->vm_file); + pgoff_t pgoff = linear_page_index(dst_vma, dst_addr); + struct page *page; + int ret; + + ret = shmem_getpage(inode, pgoff, &page, SGP_READ); + if (ret) + goto out; + if (!page) { + ret = -EFAULT; + goto out; + } + + ret = mcopy_atomic_install_pte(dst_mm, dst_pmd, dst_vma, dst_addr, + page, false, wp_copy); + if (ret) + goto out_release; + + unlock_page(page); + ret = 0; +out: + return ret; +out_release: + unlock_page(page); + put_page(page); + goto out; +} + static pmd_t *mm_alloc_pmd(struct mm_struct *mm, unsigned long address) { pgd_t *pgd; @@ -415,11 +492,16 @@ static __always_inline ssize_t mfill_atomic_pte(struct mm_struct *dst_mm, unsigned long dst_addr, unsigned long src_addr, struct page **page, - bool zeropage, + enum mcopy_atomic_mode mode, bool wp_copy) { ssize_t err; + if (mode == MCOPY_ATOMIC_CONTINUE) { + return mcontinue_atomic_pte(dst_mm, dst_pmd, dst_vma, dst_addr, + wp_copy); + } + /* * The normal page fault path for a shmem will invoke the * fault, fill the hole in the file and COW it right away. The @@ -431,7 +513,7 @@ static __always_inline ssize_t mfill_atomic_pte(struct mm_struct *dst_mm, * and not in the radix tree. */ if (!(dst_vma->vm_flags & VM_SHARED)) { - if (!zeropage) + if (mode == MCOPY_ATOMIC_NORMAL) err = mcopy_atomic_pte(dst_mm, dst_pmd, dst_vma, dst_addr, src_addr, page, wp_copy); @@ -441,7 +523,8 @@ static __always_inline ssize_t mfill_atomic_pte(struct mm_struct *dst_mm, } else { VM_WARN_ON_ONCE(wp_copy); err = shmem_mcopy_atomic_pte(dst_mm, dst_pmd, dst_vma, - dst_addr, src_addr, zeropage, + dst_addr, src_addr, + mode != MCOPY_ATOMIC_NORMAL, page); } @@ -463,7 +546,6 @@ static __always_inline ssize_t __mcopy_atomic(struct mm_struct *dst_mm, long copied; struct page *page; bool wp_copy; - bool zeropage = (mcopy_mode == MCOPY_ATOMIC_ZEROPAGE); /* * Sanitize the command parameters: @@ -526,7 +608,7 @@ static __always_inline ssize_t __mcopy_atomic(struct mm_struct *dst_mm, if (!vma_is_anonymous(dst_vma) && !vma_is_shmem(dst_vma)) goto out_unlock; - if (mcopy_mode == MCOPY_ATOMIC_CONTINUE) + if (!vma_is_shmem(dst_vma) && mcopy_mode == MCOPY_ATOMIC_CONTINUE) goto out_unlock; /* @@ -574,7 +656,7 @@ static __always_inline ssize_t __mcopy_atomic(struct mm_struct *dst_mm, BUG_ON(pmd_trans_huge(*dst_pmd)); err = mfill_atomic_pte(dst_mm, dst_pmd, dst_vma, dst_addr, - src_addr, &page, zeropage, wp_copy); + src_addr, &page, mcopy_mode, wp_copy); cond_resched(); if (unlikely(err == -ENOENT)) {