userfaultfd: protect mmap_changing with rw_sem in userfaulfd_ctx
Increments and loads to mmap_changing are always in mmap_lock critical
section. This ensures that if userspace requests event notification for
non-cooperative operations (e.g. mremap), userfaultfd operations don't
occur concurrently.
This can be achieved by using a separate read-write semaphore in
userfaultfd_ctx such that increments are done in write-mode and loads in
read-mode, thereby eliminating the dependency on mmap_lock for this
purpose.
This is a preparatory step before we replace mmap_lock usage with per-vma
locks in fill/move ioctls.
Link: https://lkml.kernel.org/r/20240215182756.3448972-3-lokeshgidra@google.com
Signed-off-by: Lokesh Gidra <lokeshgidra@google.com>
Reviewed-by: Mike Rapoport (IBM) <rppt@kernel.org>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Brian Geffon <bgeffon@google.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Jann Horn <jannh@google.com>
Cc: Kalesh Singh <kaleshsingh@google.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Nicolas Geoffray <ngeoffray@google.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Tim Murray <timmurray@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index 9cc93cc..74aad08 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -353,11 +353,11 @@ static pmd_t *mm_alloc_pmd(struct mm_struct *mm, unsigned long address)
* called with mmap_lock held, it will release mmap_lock before returning.
*/
static __always_inline ssize_t mfill_atomic_hugetlb(
+ struct userfaultfd_ctx *ctx,
struct vm_area_struct *dst_vma,
unsigned long dst_start,
unsigned long src_start,
unsigned long len,
- atomic_t *mmap_changing,
uffd_flags_t flags)
{
struct mm_struct *dst_mm = dst_vma->vm_mm;
@@ -379,6 +379,7 @@ static __always_inline ssize_t mfill_atomic_hugetlb(
* feature is not supported.
*/
if (uffd_flags_mode_is(flags, MFILL_ATOMIC_ZEROPAGE)) {
+ up_read(&ctx->map_changing_lock);
mmap_read_unlock(dst_mm);
return -EINVAL;
}
@@ -463,6 +464,7 @@ static __always_inline ssize_t mfill_atomic_hugetlb(
cond_resched();
if (unlikely(err == -ENOENT)) {
+ up_read(&ctx->map_changing_lock);
mmap_read_unlock(dst_mm);
BUG_ON(!folio);
@@ -473,12 +475,13 @@ static __always_inline ssize_t mfill_atomic_hugetlb(
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 (mmap_changing && atomic_read(mmap_changing)) {
+ if (atomic_read(&ctx->mmap_changing)) {
err = -EAGAIN;
break;
}
@@ -501,6 +504,7 @@ static __always_inline ssize_t mfill_atomic_hugetlb(
}
out_unlock:
+ up_read(&ctx->map_changing_lock);
mmap_read_unlock(dst_mm);
out:
if (folio)
@@ -512,11 +516,11 @@ static __always_inline ssize_t mfill_atomic_hugetlb(
}
#else /* !CONFIG_HUGETLB_PAGE */
/* fail at build time if gcc attempts to use this */
-extern ssize_t mfill_atomic_hugetlb(struct vm_area_struct *dst_vma,
+extern ssize_t mfill_atomic_hugetlb(struct userfaultfd_ctx *ctx,
+ struct vm_area_struct *dst_vma,
unsigned long dst_start,
unsigned long src_start,
unsigned long len,
- atomic_t *mmap_changing,
uffd_flags_t flags);
#endif /* CONFIG_HUGETLB_PAGE */
@@ -564,13 +568,13 @@ static __always_inline ssize_t mfill_atomic_pte(pmd_t *dst_pmd,
return err;
}
-static __always_inline ssize_t mfill_atomic(struct mm_struct *dst_mm,
+static __always_inline ssize_t mfill_atomic(struct userfaultfd_ctx *ctx,
unsigned long dst_start,
unsigned long src_start,
unsigned long len,
- atomic_t *mmap_changing,
uffd_flags_t flags)
{
+ struct mm_struct *dst_mm = ctx->mm;
struct vm_area_struct *dst_vma;
ssize_t err;
pmd_t *dst_pmd;
@@ -600,8 +604,9 @@ static __always_inline ssize_t mfill_atomic(struct mm_struct *dst_mm,
* 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 (mmap_changing && atomic_read(mmap_changing))
+ if (atomic_read(&ctx->mmap_changing))
goto out_unlock;
/*
@@ -633,8 +638,8 @@ static __always_inline ssize_t mfill_atomic(struct mm_struct *dst_mm,
* If this is a HUGETLB vma, pass off to appropriate routine
*/
if (is_vm_hugetlb_page(dst_vma))
- return mfill_atomic_hugetlb(dst_vma, dst_start, src_start,
- len, mmap_changing, flags);
+ return mfill_atomic_hugetlb(ctx, dst_vma, dst_start,
+ src_start, len, flags);
if (!vma_is_anonymous(dst_vma) && !vma_is_shmem(dst_vma))
goto out_unlock;
@@ -693,6 +698,7 @@ static __always_inline ssize_t mfill_atomic(struct mm_struct *dst_mm,
if (unlikely(err == -ENOENT)) {
void *kaddr;
+ up_read(&ctx->map_changing_lock);
mmap_read_unlock(dst_mm);
BUG_ON(!folio);
@@ -723,6 +729,7 @@ static __always_inline ssize_t mfill_atomic(struct mm_struct *dst_mm,
}
out_unlock:
+ up_read(&ctx->map_changing_lock);
mmap_read_unlock(dst_mm);
out:
if (folio)
@@ -733,34 +740,33 @@ static __always_inline ssize_t mfill_atomic(struct mm_struct *dst_mm,
return copied ? copied : err;
}
-ssize_t mfill_atomic_copy(struct mm_struct *dst_mm, unsigned long dst_start,
+ssize_t mfill_atomic_copy(struct userfaultfd_ctx *ctx, unsigned long dst_start,
unsigned long src_start, unsigned long len,
- atomic_t *mmap_changing, uffd_flags_t flags)
+ uffd_flags_t flags)
{
- return mfill_atomic(dst_mm, dst_start, src_start, len, mmap_changing,
+ return mfill_atomic(ctx, dst_start, src_start, len,
uffd_flags_set_mode(flags, MFILL_ATOMIC_COPY));
}
-ssize_t mfill_atomic_zeropage(struct mm_struct *dst_mm, unsigned long start,
- unsigned long len, atomic_t *mmap_changing)
+ssize_t mfill_atomic_zeropage(struct userfaultfd_ctx *ctx,
+ unsigned long start,
+ unsigned long len)
{
- return mfill_atomic(dst_mm, start, 0, len, mmap_changing,
+ return mfill_atomic(ctx, start, 0, len,
uffd_flags_set_mode(0, MFILL_ATOMIC_ZEROPAGE));
}
-ssize_t mfill_atomic_continue(struct mm_struct *dst_mm, unsigned long start,
- unsigned long len, atomic_t *mmap_changing,
- uffd_flags_t flags)
+ssize_t mfill_atomic_continue(struct userfaultfd_ctx *ctx, unsigned long start,
+ unsigned long len, uffd_flags_t flags)
{
- return mfill_atomic(dst_mm, start, 0, len, mmap_changing,
+ return mfill_atomic(ctx, start, 0, len,
uffd_flags_set_mode(flags, MFILL_ATOMIC_CONTINUE));
}
-ssize_t mfill_atomic_poison(struct mm_struct *dst_mm, unsigned long start,
- unsigned long len, atomic_t *mmap_changing,
- uffd_flags_t flags)
+ssize_t mfill_atomic_poison(struct userfaultfd_ctx *ctx, unsigned long start,
+ unsigned long len, uffd_flags_t flags)
{
- return mfill_atomic(dst_mm, start, 0, len, mmap_changing,
+ return mfill_atomic(ctx, start, 0, len,
uffd_flags_set_mode(flags, MFILL_ATOMIC_POISON));
}
@@ -793,10 +799,10 @@ long uffd_wp_range(struct vm_area_struct *dst_vma,
return ret;
}
-int mwriteprotect_range(struct mm_struct *dst_mm, unsigned long start,
- unsigned long len, bool enable_wp,
- atomic_t *mmap_changing)
+int mwriteprotect_range(struct userfaultfd_ctx *ctx, unsigned long start,
+ unsigned long len, bool enable_wp)
{
+ struct mm_struct *dst_mm = ctx->mm;
unsigned long end = start + len;
unsigned long _start, _end;
struct vm_area_struct *dst_vma;
@@ -820,8 +826,9 @@ int mwriteprotect_range(struct mm_struct *dst_mm, unsigned long start,
* 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 (mmap_changing && atomic_read(mmap_changing))
+ if (atomic_read(&ctx->mmap_changing))
goto out_unlock;
err = -ENOENT;
@@ -850,6 +857,7 @@ int mwriteprotect_range(struct mm_struct *dst_mm, unsigned long start,
err = 0;
}
out_unlock:
+ up_read(&ctx->map_changing_lock);
mmap_read_unlock(dst_mm);
return err;
}
