From patchwork Fri Jan 26 18:26:47 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Lokesh Gidra X-Patchwork-Id: 13533162 X-Patchwork-Delegate: paul@paul-moore.com Received: from mail-yw1-f201.google.com (mail-yw1-f201.google.com [209.85.128.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 275AA20DD4 for ; Fri, 26 Jan 2024 18:26:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1706293617; cv=none; b=tfnDoT4vY/u+yYlBxrjcHqNEkDnd7hCB69ZQLmaaTvvzIYPL9fz6tO46rc5jb5Fh0n+7SDIIXV9LczBsg84NZ6jdUd+tCRqyaulyXaDHfuUyB2STmiUNR2i7ooPgW0oABTC7BrUONEtfLEOs0r4OZra2vhpfhaqwFg7GVEIGNL0= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1706293617; c=relaxed/simple; bh=o3RxoKEoGAMsrFl/gj9m84T613VSvhnEZzjCZFnZK5o=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=p0LekUa7621oROPb2KxARiv+BcKCiHIyG+4ucoDH+I/3u5/DWe49YO4z8JDUQXkhqvxF5ZAE1P1gVLyVY17PFEq7AT1EAlVxx8LFLAGreqnHukrMm2ARfBwNXul4lXEoEMk4/LSFImGLMsJQnA1jQCTC7I92cBSxFGQUQCKWW2k= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--lokeshgidra.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=QXfr0lCV; arc=none smtp.client-ip=209.85.128.201 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--lokeshgidra.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="QXfr0lCV" Received: by mail-yw1-f201.google.com with SMTP id 00721157ae682-5f874219ff9so8686377b3.0 for ; Fri, 26 Jan 2024 10:26:55 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1706293614; x=1706898414; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=uLXJpcEgAvHLQ8+bquI5HaOs2SY4k/xeWqEkBYhbiw0=; b=QXfr0lCVIA/VWR19QIkaqlJkq8DXwIi5BAHiN3i9TzKydxcpI9JpYzh3zE/OYgvhST ekPXAzomBtsYWAQisdLWTb9ZL/DScyTu5farAiMxpNa/Q1R+0YGZTzEvPkpZFEaH0CnV YGtRwOaeKDjcf2kPtuN++PGFa5Fg8hWPV4e3HCV8D99OKuwpobExWMrtb/YOhEXXT2jO PCb+e/+jesiHRofWIFNF87/1azNVyhBZyJMIIauvvOoir5TfVRx1E2ruSz4dt5n8cBQg d9WBI7b4FNDzrPqgs4kLbY0SeAcvaQDNSldkunF3XGbAAgIIyy0af2GxDPV6BQY8WfmT WRBg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1706293614; x=1706898414; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=uLXJpcEgAvHLQ8+bquI5HaOs2SY4k/xeWqEkBYhbiw0=; b=HKCewcRaOX4iJeYxMTq1UXs+iwcPNa/muaIzA/QocQmdgxt6g36iCrrNQzwvlL7zkW 6h+E3nPPi/6Ue3UFvyqeid6gk65nEcRhA1czQG094LePl3/DH7/+QvZa+g7Na0O/k2Cg NRuGfkiF5v5GNFmpxlSkS9/BKGYaPD65BcEaoS0xclIEXgp2Q6vss1oLXBWumP1vaFMQ 84CeqTfGvXJ75MImQAdwzY6l6FKMXAoLYae5FenqCYICwhpoSpt2R91H+YkbJVIqhEpw +J5/0rmSyBEL6N2u4BHpn3CUoO8keh+oeAFlBNwT+ToJvgUOu8FeHxF8QGToMrp+9y/n C96g== X-Gm-Message-State: AOJu0YzWal7IqwhCYFkBm108ATHHESgddOc5CaVzvh93u1kFpBM4ElzJ 9VKfG13JYA9/7R8+xo66qaNFvNDXd3witJjbe0fmwoFmZLxFeww5G+hpwgEEj4/FPS4p9mG0tX+ 08VgnHdZZAdIrb0ZlFajzRQ== X-Google-Smtp-Source: AGHT+IGt2/BA8dj3t3+f3CDFRNY8WvXgtUOL2IcXoo5TOnIKymbSZPVcMF8fo+tUfgFLJ3Qz79dJcQPFBkAu0Cw8KQ== X-Received: from lg.mtv.corp.google.com ([2620:15c:211:202:cc8a:c6c9:a475:ebf]) (user=lokeshgidra job=sendgmr) by 2002:a81:4cd3:0:b0:5fc:7f94:da64 with SMTP id z202-20020a814cd3000000b005fc7f94da64mr95373ywa.5.1706293614376; Fri, 26 Jan 2024 10:26:54 -0800 (PST) Date: Fri, 26 Jan 2024 10:26:47 -0800 In-Reply-To: <20240126182647.2748949-1-lokeshgidra@google.com> Precedence: bulk X-Mailing-List: selinux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20240126182647.2748949-1-lokeshgidra@google.com> X-Mailer: git-send-email 2.43.0.429.g432eaa2c6b-goog Message-ID: <20240126182647.2748949-3-lokeshgidra@google.com> Subject: [PATCH 3/3] userfaultfd: use per-vma locks in userfaultfd operations From: Lokesh Gidra To: akpm@linux-foundation.org Cc: lokeshgidra@google.com, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, selinux@vger.kernel.org, surenb@google.com, kernel-team@android.com, aarcange@redhat.com, peterx@redhat.com, david@redhat.com, axelrasmussen@google.com, bgeffon@google.com, willy@infradead.org, jannh@google.com, kaleshsingh@google.com, ngeoffray@google.com, timmurray@google.com, rppt@kernel.org Performing userfaultfd operations (like copy/move etc.) in critical section of mmap_lock (read-mode) has shown significant contention on the lock when operations requiring the lock in write-mode are taking place concurrently. We can use per-vma locks instead to significantly reduce the contention issue. All userfaultfd operations, except write-protect, opportunistically use per-vma locks to lock vmas. Write-protect operation requires mmap_lock as it iterates over multiple vmas. Signed-off-by: Lokesh Gidra --- fs/userfaultfd.c | 14 +---- mm/userfaultfd.c | 160 ++++++++++++++++++++++++++++++++++------------- 2 files changed, 117 insertions(+), 57 deletions(-) diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c index 5aaf248d3107..faa10ed3788f 100644 --- a/fs/userfaultfd.c +++ b/fs/userfaultfd.c @@ -2005,18 +2005,8 @@ static int userfaultfd_move(struct userfaultfd_ctx *ctx, return -EINVAL; if (mmget_not_zero(mm)) { - mmap_read_lock(mm); - - /* Re-check after taking map_changing_lock */ - down_read(&ctx->map_changing_lock); - if (likely(!atomic_read(&ctx->mmap_changing))) - ret = move_pages(ctx, mm, uffdio_move.dst, uffdio_move.src, - uffdio_move.len, uffdio_move.mode); - else - ret = -EINVAL; - up_read(&ctx->map_changing_lock); - - mmap_read_unlock(mm); + ret = move_pages(ctx, mm, uffdio_move.dst, uffdio_move.src, + uffdio_move.len, uffdio_move.mode); mmput(mm); } else { return -ESRCH; diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index a66b4d62a361..9be643308f05 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -19,20 +19,39 @@ #include #include "internal.h" -static __always_inline -struct vm_area_struct *find_dst_vma(struct mm_struct *dst_mm, - unsigned long dst_start, - unsigned long len) +void unpin_vma(struct mm_struct *mm, struct vm_area_struct *vma, bool *mmap_locked) +{ + BUG_ON(!vma && !*mmap_locked); + + if (*mmap_locked) { + mmap_read_unlock(mm); + *mmap_locked = false; + } else + vma_end_read(vma); +} + +/* + * Search for VMA and make sure it is stable either by locking it or taking + * mmap_lock. + */ +struct vm_area_struct *find_and_pin_dst_vma(struct mm_struct *dst_mm, + unsigned long dst_start, + unsigned long len, + bool *mmap_locked) { + struct vm_area_struct *dst_vma = lock_vma_under_rcu(dst_mm, dst_start); + if (!dst_vma) { + mmap_read_lock(dst_mm); + *mmap_locked = true; + dst_vma = find_vma(dst_mm, dst_start); + } + /* * Make sure that the dst range is both valid and fully within a * single existing vma. */ - struct vm_area_struct *dst_vma; - - dst_vma = find_vma(dst_mm, dst_start); if (!range_in_vma(dst_vma, dst_start, dst_start + len)) - return NULL; + goto unpin; /* * Check the vma is registered in uffd, this is required to @@ -40,9 +59,13 @@ struct vm_area_struct *find_dst_vma(struct mm_struct *dst_mm, * time. */ if (!dst_vma->vm_userfaultfd_ctx.ctx) - return NULL; + goto unpin; return dst_vma; + +unpin: + unpin_vma(dst_mm, dst_vma, mmap_locked); + return NULL; } /* Check if dst_addr is outside of file's size. Must be called with ptl held. */ @@ -350,7 +373,8 @@ static pmd_t *mm_alloc_pmd(struct mm_struct *mm, unsigned long address) #ifdef CONFIG_HUGETLB_PAGE /* * mfill_atomic processing for HUGETLB vmas. Note that this routine is - * called with mmap_lock held, it will release mmap_lock before returning. + * called with either vma-lock or mmap_lock held, it will release the lock + * before returning. */ static __always_inline ssize_t mfill_atomic_hugetlb( struct userfaultfd_ctx *ctx, @@ -358,7 +382,8 @@ static __always_inline ssize_t mfill_atomic_hugetlb( unsigned long dst_start, unsigned long src_start, unsigned long len, - uffd_flags_t flags) + uffd_flags_t flags, + bool *mmap_locked) { struct mm_struct *dst_mm = dst_vma->vm_mm; int vm_shared = dst_vma->vm_flags & VM_SHARED; @@ -380,7 +405,7 @@ static __always_inline ssize_t mfill_atomic_hugetlb( */ if (uffd_flags_mode_is(flags, MFILL_ATOMIC_ZEROPAGE)) { up_read(&ctx->map_changing_lock); - mmap_read_unlock(dst_mm); + unpin_vma(dst_mm, dst_vma, mmap_locked); return -EINVAL; } @@ -404,12 +429,25 @@ static __always_inline ssize_t mfill_atomic_hugetlb( */ if (!dst_vma) { err = -ENOENT; - dst_vma = find_dst_vma(dst_mm, dst_start, len); - if (!dst_vma || !is_vm_hugetlb_page(dst_vma)) - goto out_unlock; + dst_vma = find_and_pin_dst_vma(dst_mm, dst_start, + len, mmap_locked); + if (!dst_vma) + goto out; + if (!is_vm_hugetlb_page(dst_vma)) + goto out_unlock_vma; err = -EINVAL; if (vma_hpagesize != vma_kernel_pagesize(dst_vma)) + goto out_unlock_vma; + + /* + * If memory mappings are changing because of non-cooperative + * operation (e.g. mremap) running in parallel, bail out and + * request the user to retry later + */ + down_read(&ctx->map_changing_lock); + err = -EAGAIN; + if (atomic_read(&ctx->mmap_changing)) goto out_unlock; vm_shared = dst_vma->vm_flags & VM_SHARED; @@ -465,7 +503,7 @@ static __always_inline ssize_t mfill_atomic_hugetlb( if (unlikely(err == -ENOENT)) { up_read(&ctx->map_changing_lock); - mmap_read_unlock(dst_mm); + unpin_vma(dst_mm, dst_vma, mmap_locked); BUG_ON(!folio); err = copy_folio_from_user(folio, @@ -474,8 +512,6 @@ static __always_inline ssize_t mfill_atomic_hugetlb( err = -EFAULT; goto out; } - mmap_read_lock(dst_mm); - down_read(&ctx->map_changing_lock); dst_vma = NULL; goto retry; @@ -496,7 +532,8 @@ static __always_inline ssize_t mfill_atomic_hugetlb( out_unlock: up_read(&ctx->map_changing_lock); - mmap_read_unlock(dst_mm); +out_unlock_vma: + unpin_vma(dst_mm, dst_vma, mmap_locked); out: if (folio) folio_put(folio); @@ -512,7 +549,8 @@ extern ssize_t mfill_atomic_hugetlb(struct userfaultfd_ctx *ctx, unsigned long dst_start, unsigned long src_start, unsigned long len, - uffd_flags_t flags); + uffd_flags_t flags, + bool *mmap_locked); #endif /* CONFIG_HUGETLB_PAGE */ static __always_inline ssize_t mfill_atomic_pte(pmd_t *dst_pmd, @@ -572,6 +610,7 @@ static __always_inline ssize_t mfill_atomic(struct userfaultfd_ctx *ctx, unsigned long src_addr, dst_addr; long copied; struct folio *folio; + bool mmap_locked = false; /* * Sanitize the command parameters: @@ -588,7 +627,14 @@ static __always_inline ssize_t mfill_atomic(struct userfaultfd_ctx *ctx, copied = 0; folio = NULL; retry: - mmap_read_lock(dst_mm); + /* + * Make sure the vma is not shared, that the dst range is + * both valid and fully within a single existing vma. + */ + err = -ENOENT; + dst_vma = find_and_pin_dst_vma(dst_mm, dst_start, len, &mmap_locked); + if (!dst_vma) + goto out; /* * If memory mappings are changing because of non-cooperative @@ -600,15 +646,6 @@ static __always_inline ssize_t mfill_atomic(struct userfaultfd_ctx *ctx, if (atomic_read(&ctx->mmap_changing)) goto out_unlock; - /* - * Make sure the vma is not shared, that the dst range is - * both valid and fully within a single existing vma. - */ - err = -ENOENT; - dst_vma = find_dst_vma(dst_mm, dst_start, len); - if (!dst_vma) - goto out_unlock; - err = -EINVAL; /* * shmem_zero_setup is invoked in mmap for MAP_ANONYMOUS|MAP_SHARED but @@ -629,8 +666,8 @@ static __always_inline ssize_t mfill_atomic(struct userfaultfd_ctx *ctx, * If this is a HUGETLB vma, pass off to appropriate routine */ if (is_vm_hugetlb_page(dst_vma)) - return mfill_atomic_hugetlb(ctx, dst_vma, dst_start, - src_start, len, flags); + return mfill_atomic_hugetlb(ctx, dst_vma, dst_start, src_start + len, flags, &mmap_locked); if (!vma_is_anonymous(dst_vma) && !vma_is_shmem(dst_vma)) goto out_unlock; @@ -690,7 +727,8 @@ static __always_inline ssize_t mfill_atomic(struct userfaultfd_ctx *ctx, void *kaddr; up_read(&ctx->map_changing_lock); - mmap_read_unlock(dst_mm); + unpin_vma(dst_mm, dst_vma, &mmap_locked); + BUG_ON(!folio); kaddr = kmap_local_folio(folio, 0); @@ -721,7 +759,7 @@ static __always_inline ssize_t mfill_atomic(struct userfaultfd_ctx *ctx, out_unlock: up_read(&ctx->map_changing_lock); - mmap_read_unlock(dst_mm); + unpin_vma(dst_mm, dst_vma, &mmap_locked); out: if (folio) folio_put(folio); @@ -1243,8 +1281,6 @@ static int validate_move_areas(struct userfaultfd_ctx *ctx, * @len: length of the virtual memory range * @mode: flags from uffdio_move.mode * - * Must be called with mmap_lock held for read. - * * move_pages() remaps arbitrary anonymous pages atomically in zero * copy. It only works on non shared anonymous pages because those can * be relocated without generating non linear anon_vmas in the rmap @@ -1320,6 +1356,7 @@ ssize_t move_pages(struct userfaultfd_ctx *ctx, struct mm_struct *mm, pmd_t *src_pmd, *dst_pmd; long err = -EINVAL; ssize_t moved = 0; + bool mmap_locked = false; /* Sanitize the command parameters. */ if (WARN_ON_ONCE(src_start & ~PAGE_MASK) || @@ -1332,28 +1369,52 @@ ssize_t move_pages(struct userfaultfd_ctx *ctx, struct mm_struct *mm, WARN_ON_ONCE(dst_start + len <= dst_start)) goto out; + dst_vma = NULL; + src_vma = lock_vma_under_rcu(mm, src_start); + if (src_vma) { + dst_vma = lock_vma_under_rcu(mm, dst_start); + if (!dst_vma) + vma_end_read(src_vma); + } + + /* If we failed to lock both VMAs, fall back to mmap_lock */ + if (!dst_vma) { + mmap_read_lock(mm); + mmap_locked = true; + src_vma = find_vma(mm, src_start); + if (!src_vma) + goto out_unlock_mmap; + dst_vma = find_vma(mm, dst_start); + if (!dst_vma) + goto out_unlock_mmap; + } + + /* Re-check after taking map_changing_lock */ + down_read(&ctx->map_changing_lock); + if (likely(atomic_read(&ctx->mmap_changing))) { + err = -EAGAIN; + goto out_unlock; + } /* * Make sure the vma is not shared, that the src and dst remap * ranges are both valid and fully within a single existing * vma. */ - src_vma = find_vma(mm, src_start); - if (!src_vma || (src_vma->vm_flags & VM_SHARED)) - goto out; + if (src_vma->vm_flags & VM_SHARED) + goto out_unlock; if (src_start < src_vma->vm_start || src_start + len > src_vma->vm_end) - goto out; + goto out_unlock; - dst_vma = find_vma(mm, dst_start); - if (!dst_vma || (dst_vma->vm_flags & VM_SHARED)) - goto out; + if (dst_vma->vm_flags & VM_SHARED) + goto out_unlock; if (dst_start < dst_vma->vm_start || dst_start + len > dst_vma->vm_end) - goto out; + goto out_unlock; err = validate_move_areas(ctx, src_vma, dst_vma); if (err) - goto out; + goto out_unlock; for (src_addr = src_start, dst_addr = dst_start; src_addr < src_start + len;) { @@ -1475,6 +1536,15 @@ ssize_t move_pages(struct userfaultfd_ctx *ctx, struct mm_struct *mm, moved += step_size; } +out_unlock: + up_read(&ctx->map_changing_lock); +out_unlock_mmap: + if (mmap_locked) + mmap_read_unlock(mm); + else { + vma_end_read(dst_vma); + vma_end_read(src_vma); + } out: VM_WARN_ON(moved < 0); VM_WARN_ON(err > 0);