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If we fail then fall back to locking mmap-lock in read-mode. Write-protect operation requires mmap_lock as it iterates over multiple vmas. Signed-off-by: Lokesh Gidra --- fs/userfaultfd.c | 13 +-- include/linux/userfaultfd_k.h | 5 +- mm/userfaultfd.c | 175 +++++++++++++++++++++++----------- 3 files changed, 122 insertions(+), 71 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/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/userfaultfd.c b/mm/userfaultfd.c index 6e2ca04ab04d..d55bf18b80db 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, @@ -474,17 +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); - /* - * 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 +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); @@ -521,7 +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, @@ -581,6 +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: @@ -597,7 +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 @@ -609,15 +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 @@ -638,8 +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; @@ -699,7 +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); @@ -730,7 +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); @@ -1285,8 +1314,6 @@ 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 @@ -1353,15 +1380,16 @@ 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; long err = -EINVAL; ssize_t moved = 0; + bool mmap_locked = false; /* Sanitize the command parameters. */ if (WARN_ON_ONCE(src_start & ~PAGE_MASK) || @@ -1374,28 +1402,52 @@ 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;) { @@ -1512,6 +1564,15 @@ 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);