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Mon, 05 Feb 2024 17:09:58 -0800 (PST) Date: Mon, 5 Feb 2024 17:09:19 -0800 In-Reply-To: <20240206010919.1109005-1-lokeshgidra@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20240206010919.1109005-1-lokeshgidra@google.com> X-Mailer: git-send-email 2.43.0.594.gd9cf4e227d-goog Message-ID: <20240206010919.1109005-4-lokeshgidra@google.com> Subject: [PATCH v3 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, Liam.Howlett@oracle.com Content-Type: text/plain; charset="UTF-8" All userfaultfd operations, except write-protect, opportunistically use per-vma locks to lock vmas. On failure, attempt again inside mmap_lock critical section. Write-protect operation requires mmap_lock as it iterates over multiple vmas. Signed-off-by: Lokesh Gidra --- fs/userfaultfd.c | 13 +- include/linux/mm.h | 16 +++ include/linux/userfaultfd_k.h | 5 +- mm/memory.c | 48 +++++++ mm/userfaultfd.c | 242 +++++++++++++++++++++------------- 5 files changed, 222 insertions(+), 102 deletions(-) diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c index c00a021bcce4..60dcfafdc11a 100644 --- a/fs/userfaultfd.c +++ b/fs/userfaultfd.c @@ -2005,17 +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 = -EAGAIN; - up_read(&ctx->map_changing_lock); - mmap_read_unlock(mm); + ret = move_pages(ctx, uffdio_move.dst, uffdio_move.src, + uffdio_move.len, uffdio_move.mode); mmput(mm); } else { return -ESRCH; diff --git a/include/linux/mm.h b/include/linux/mm.h index 0d1f98ab0c72..e69dfe2edcce 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -753,6 +753,11 @@ static inline void release_fault_lock(struct vm_fault *vmf) mmap_read_unlock(vmf->vma->vm_mm); } +static inline void unlock_vma(struct mm_struct *mm, struct vm_area_struct *vma) +{ + vma_end_read(vma); +} + static inline void assert_fault_locked(struct vm_fault *vmf) { if (vmf->flags & FAULT_FLAG_VMA_LOCK) @@ -774,6 +779,9 @@ static inline void vma_assert_write_locked(struct vm_area_struct *vma) { mmap_assert_write_locked(vma->vm_mm); } static inline void vma_mark_detached(struct vm_area_struct *vma, bool detached) {} +static inline void vma_acquire_read_lock(struct vm_area_struct *vma) { + mmap_assert_locked(vma->vm_mm); +} static inline struct vm_area_struct *lock_vma_under_rcu(struct mm_struct *mm, unsigned long address) @@ -786,6 +794,11 @@ static inline void release_fault_lock(struct vm_fault *vmf) mmap_read_unlock(vmf->vma->vm_mm); } +static inline void unlock_vma(struct mm_struct *mm, struct vm_area_struct *vma) +{ + mmap_read_unlock(mm); +} + static inline void assert_fault_locked(struct vm_fault *vmf) { mmap_assert_locked(vmf->vma->vm_mm); @@ -794,6 +807,9 @@ static inline void assert_fault_locked(struct vm_fault *vmf) #endif /* CONFIG_PER_VMA_LOCK */ extern const struct vm_operations_struct vma_dummy_vm_ops; +extern struct vm_area_struct *lock_vma(struct mm_struct *mm, + unsigned long address, + bool prepare_anon); /* * WARNING: vma_init does not initialize vma->vm_lock. diff --git a/include/linux/userfaultfd_k.h b/include/linux/userfaultfd_k.h index 3210c3552976..05d59f74fc88 100644 --- a/include/linux/userfaultfd_k.h +++ b/include/linux/userfaultfd_k.h @@ -138,9 +138,8 @@ extern long uffd_wp_range(struct vm_area_struct *vma, /* move_pages */ void double_pt_lock(spinlock_t *ptl1, spinlock_t *ptl2); void double_pt_unlock(spinlock_t *ptl1, spinlock_t *ptl2); -ssize_t move_pages(struct userfaultfd_ctx *ctx, struct mm_struct *mm, - unsigned long dst_start, unsigned long src_start, - unsigned long len, __u64 flags); +ssize_t move_pages(struct userfaultfd_ctx *ctx, unsigned long dst_start, + unsigned long src_start, unsigned long len, __u64 flags); int move_pages_huge_pmd(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd, pmd_t dst_pmdval, struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma, diff --git a/mm/memory.c b/mm/memory.c index b05fd28dbce1..393ab3b0d6f3 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -5760,8 +5760,56 @@ struct vm_area_struct *lock_vma_under_rcu(struct mm_struct *mm, count_vm_vma_lock_event(VMA_LOCK_ABORT); return NULL; } + +static void vma_acquire_read_lock(struct vm_area_struct *vma) +{ + /* + * We cannot use vma_start_read() as it may fail due to false locked + * (see comment in vma_start_read()). We can avoid that by directly + * locking vm_lock under mmap_lock, which guarantees that nobody could + * have locked the vma for write (vma_start_write()). + */ + mmap_assert_locked(vma->vm_mm); + down_read(&vma->vm_lock->lock); +} #endif /* CONFIG_PER_VMA_LOCK */ +/* + * lock_vma() - Lookup and lock VMA corresponding to @address. + * @prepare_anon: If true, then prepare the VMA (if anonymous) with anon_vma. + * + * Should be called without holding mmap_lock. VMA should be unlocked after use + * with unlock_vma(). + * + * Return: A locked VMA containing @address, NULL of no VMA is found, or + * -ENOMEM if anon_vma couldn't be allocated. + */ +struct vm_area_struct *lock_vma(struct mm_struct *mm, + unsigned long address, + bool prepare_anon) +{ + struct vm_area_struct *vma; + + vma = lock_vma_under_rcu(mm, address); + + if (vma) + return vma; + + mmap_read_lock(mm); + vma = vma_lookup(mm, address); + if (vma) { + if (prepare_anon && vma_is_anonymous(vma) && + anon_vma_prepare(vma)) + vma = ERR_PTR(-ENOMEM); + else + vma_acquire_read_lock(vma); + } + + if (IS_ENABLED(CONFIG_PER_VMA_LOCK) || !vma || PTR_ERR(vma) == -ENOMEM) + mmap_read_unlock(mm); + return vma; +} + #ifndef __PAGETABLE_P4D_FOLDED /* * Allocate p4d page table. diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index 74aad0831e40..64e22e467e4f 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -19,20 +19,25 @@ #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) +/* Search for VMA and make sure it is valid. */ +static struct vm_area_struct *find_and_lock_dst_vma(struct mm_struct *dst_mm, + unsigned long dst_start, + unsigned long len) { - /* - * 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; + /* Ensure anon_vma is assigned for anonymous vma */ + dst_vma = lock_vma(dst_mm, dst_start, true); + + if (!dst_vma) + return ERR_PTR(-ENOENT); + + if (PTR_ERR(dst_vma) == -ENOMEM) + return dst_vma; + + /* Make sure that the dst range is fully within dst_vma. */ + if (dst_start + len > dst_vma->vm_end) + goto out_unlock; /* * Check the vma is registered in uffd, this is required to @@ -40,9 +45,12 @@ struct vm_area_struct *find_dst_vma(struct mm_struct *dst_mm, * time. */ if (!dst_vma->vm_userfaultfd_ctx.ctx) - return NULL; + goto out_unlock; return dst_vma; +out_unlock: + unlock_vma(dst_mm, dst_vma); + return ERR_PTR(-ENOENT); } /* Check if dst_addr is outside of file's size. Must be called with ptl held. */ @@ -350,7 +358,8 @@ 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, @@ -361,7 +370,6 @@ static __always_inline ssize_t mfill_atomic_hugetlb( uffd_flags_t flags) { struct mm_struct *dst_mm = dst_vma->vm_mm; - int vm_shared = dst_vma->vm_flags & VM_SHARED; ssize_t err; pte_t *dst_pte; unsigned long src_addr, dst_addr; @@ -380,7 +388,7 @@ 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); + unlock_vma(dst_mm, dst_vma); return -EINVAL; } @@ -403,24 +411,28 @@ static __always_inline ssize_t mfill_atomic_hugetlb( * retry, dst_vma will be set to NULL and we must lookup again. */ if (!dst_vma) { + dst_vma = find_and_lock_dst_vma(dst_mm, dst_start, len); + if (IS_ERR(dst_vma)) { + err = PTR_ERR(dst_vma); + goto out; + } + err = -ENOENT; - dst_vma = find_dst_vma(dst_mm, dst_start, len); - if (!dst_vma || !is_vm_hugetlb_page(dst_vma)) - goto out_unlock; + if (!is_vm_hugetlb_page(dst_vma)) + goto out_unlock_vma; err = -EINVAL; if (vma_hpagesize != vma_kernel_pagesize(dst_vma)) - goto out_unlock; + goto out_unlock_vma; - vm_shared = dst_vma->vm_flags & VM_SHARED; - } - - /* - * If not shared, ensure the dst_vma has a anon_vma. - */ - err = -ENOMEM; - if (!vm_shared) { - if (unlikely(anon_vma_prepare(dst_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; } @@ -465,7 +477,7 @@ static __always_inline ssize_t mfill_atomic_hugetlb( if (unlikely(err == -ENOENT)) { up_read(&ctx->map_changing_lock); - mmap_read_unlock(dst_mm); + unlock_vma(dst_mm, dst_vma); BUG_ON(!folio); err = copy_folio_from_user(folio, @@ -474,17 +486,6 @@ static __always_inline ssize_t mfill_atomic_hugetlb( err = -EFAULT; goto out; } - mmap_read_lock(dst_mm); - down_read(&ctx->map_changing_lock); - /* - * 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 - */ - if (atomic_read(&ctx->mmap_changing)) { - err = -EAGAIN; - break; - } dst_vma = NULL; goto retry; @@ -505,7 +506,8 @@ static __always_inline ssize_t mfill_atomic_hugetlb( out_unlock: up_read(&ctx->map_changing_lock); - mmap_read_unlock(dst_mm); +out_unlock_vma: + unlock_vma(dst_mm, dst_vma); out: if (folio) folio_put(folio); @@ -597,7 +599,15 @@ 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. + */ + dst_vma = find_and_lock_dst_vma(dst_mm, dst_start, len); + if (IS_ERR(dst_vma)) { + err = PTR_ERR(dst_vma); + goto out; + } /* * If memory mappings are changing because of non-cooperative @@ -609,15 +619,6 @@ 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 @@ -647,16 +648,6 @@ static __always_inline ssize_t mfill_atomic(struct userfaultfd_ctx *ctx, uffd_flags_mode_is(flags, MFILL_ATOMIC_CONTINUE)) goto out_unlock; - /* - * Ensure the dst_vma has a anon_vma or this page - * would get a NULL anon_vma when moved in the - * dst_vma. - */ - err = -ENOMEM; - if (!(dst_vma->vm_flags & VM_SHARED) && - unlikely(anon_vma_prepare(dst_vma))) - goto out_unlock; - while (src_addr < src_start + len) { pmd_t dst_pmdval; @@ -699,7 +690,8 @@ static __always_inline ssize_t mfill_atomic(struct userfaultfd_ctx *ctx, void *kaddr; up_read(&ctx->map_changing_lock); - mmap_read_unlock(dst_mm); + unlock_vma(dst_mm, dst_vma); + BUG_ON(!folio); kaddr = kmap_local_folio(folio, 0); @@ -730,7 +722,7 @@ static __always_inline ssize_t mfill_atomic(struct userfaultfd_ctx *ctx, out_unlock: up_read(&ctx->map_changing_lock); - mmap_read_unlock(dst_mm); + unlock_vma(dst_mm, dst_vma); out: if (folio) folio_put(folio); @@ -1267,16 +1259,82 @@ static int validate_move_areas(struct userfaultfd_ctx *ctx, if (!vma_is_anonymous(src_vma) || !vma_is_anonymous(dst_vma)) return -EINVAL; - /* - * Ensure the dst_vma has a anon_vma or this page - * would get a NULL anon_vma when moved in the - * dst_vma. - */ - if (unlikely(anon_vma_prepare(dst_vma))) - return -ENOMEM; + return 0; +} + +#ifdef CONFIG_PER_VMA_LOCK +static int find_and_lock_move_vmas(struct mm_struct *mm, + unsigned long dst_start, + unsigned long src_start, + struct vm_area_struct **dst_vmap, + struct vm_area_struct **src_vmap) +{ + int err; + + /* There is no need to prepare anon_vma for src_vma */ + *src_vmap = lock_vma(mm, src_start, false); + if (!*src_vmap) + return -ENOENT; + + /* Ensure anon_vma is assigned for anonymous vma */ + *dst_vmap = lock_vma(mm, dst_start, true); + err = -ENOENT; + if (!*dst_vmap) + goto out_unlock; + + err = -ENOMEM; + if (PTR_ERR(*dst_vmap) == -ENOMEM) + goto out_unlock; return 0; +out_unlock: + unlock_vma(mm, *src_vmap); + return err; +} + +static void unlock_move_vmas(struct mm_struct *mm, + struct vm_area_struct *dst_vma, + struct vm_area_struct *src_vma) +{ + unlock_vma(mm, dst_vma); + unlock_vma(mm, src_vma); } +#else +static int find_and_lock_move_vmas(struct mm_struct *mm, + unsigned long dst_start, + unsigned long src_start, + struct vm_area_struct **dst_vmap, + struct vm_area_struct **src_vmap) +{ + int err = -ENOENT; + mmap_read_lock(mm); + + *src_vmap = vma_lookup(mm, src_start); + if (!*src_vmap) + goto out_unlock; + + *dst_vmap = vma_lookup(mm, dst_start); + if (!*dst_vmap) + goto out_unlock; + + /* Ensure anon_vma is assigned */ + err = -ENOMEM; + if (vma_is_anonymous(*dst_vmap) && !anon_vma_prepare(*dst_vmap)) + goto out_unlock; + + return 0; +out_unlock: + mmap_read_unlock(mm); + return err; +} + +static void unlock_move_vmas(struct mm_struct *mm, + struct vm_area_struct *dst_vma, + struct vm_area_struct *src_vma) +{ + mmap_read_unlock(mm); +} +#endif /** * move_pages - move arbitrary anonymous pages of an existing vma @@ -1287,8 +1345,6 @@ 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 @@ -1355,10 +1411,10 @@ static int validate_move_areas(struct userfaultfd_ctx *ctx, * could be obtained. This is the only additional complexity added to * the rmap code to provide this anonymous page remapping functionality. */ -ssize_t move_pages(struct userfaultfd_ctx *ctx, struct mm_struct *mm, - unsigned long dst_start, unsigned long src_start, - unsigned long len, __u64 mode) +ssize_t move_pages(struct userfaultfd_ctx *ctx, unsigned long dst_start, + unsigned long src_start, unsigned long len, __u64 mode) { + struct mm_struct *mm = ctx->mm; struct vm_area_struct *src_vma, *dst_vma; unsigned long src_addr, dst_addr; pmd_t *src_pmd, *dst_pmd; @@ -1376,28 +1432,35 @@ ssize_t move_pages(struct userfaultfd_ctx *ctx, struct mm_struct *mm, WARN_ON_ONCE(dst_start + len <= dst_start)) goto out; + err = find_and_lock_move_vmas(mm, dst_start, src_start, + &dst_vma, &src_vma); + if (err) + goto out; + + /* 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_start < src_vma->vm_start || - src_start + len > src_vma->vm_end) - goto out; + if (src_vma->vm_flags & VM_SHARED) + goto out_unlock; + if (src_start + len > src_vma->vm_end) + goto out_unlock; - dst_vma = find_vma(mm, dst_start); - if (!dst_vma || (dst_vma->vm_flags & VM_SHARED)) - goto out; - if (dst_start < dst_vma->vm_start || - dst_start + len > dst_vma->vm_end) - goto out; + if (dst_vma->vm_flags & VM_SHARED) + goto out_unlock; + if (dst_start + len > dst_vma->vm_end) + 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;) { @@ -1514,6 +1577,9 @@ ssize_t move_pages(struct userfaultfd_ctx *ctx, struct mm_struct *mm, moved += step_size; } +out_unlock: + up_read(&ctx->map_changing_lock); + unlock_move_vmas(mm, dst_vma, src_vma); out: VM_WARN_ON(moved < 0); VM_WARN_ON(err > 0); -- 2.43.0.594.gd9cf4e227d-goog