Rather than use remap_pfn_range() for this and manually free later,
switch to using vm_insert_page() and have it Just Work.
This requires a bit of effort on the mmap lookup side, as the ctx
uring_lock isn't held, which otherwise protects buffer_lists from being
torn down, and it's not safe to grab from mmap context that would
introduce an ABBA deadlock between the mmap lock and the ctx uring_lock.
Instead, lookup the buffer_list under RCU, as the the list is RCU freed
already. Use the existing reference count to determine whether it's
possible to safely grab a reference to it (eg if it's not zero already),
and drop that reference when done with the mapping. If the mmap
reference is the last one, the buffer_list and the associated memory can
go away, since the vma insertion has references to the inserted pages at
that point.
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
---
include/linux/io_uring_types.h | 3 -
io_uring/io_uring.c | 30 ++----
io_uring/io_uring.h | 3 -
io_uring/kbuf.c | 178 +++++++++++++--------------------
io_uring/kbuf.h | 4 +-
5 files changed, 82 insertions(+), 136 deletions(-)
diff --git a/include/linux/io_uring_types.h b/include/linux/io_uring_types.h
index c9a1952a383a..f37caff64d05 100644
--- a/include/linux/io_uring_types.h
+++ b/include/linux/io_uring_types.h
@@ -370,9 +370,6 @@ struct io_ring_ctx {
struct list_head io_buffers_cache;
- /* deferred free list, protected by ->uring_lock */
- struct hlist_head io_buf_list;
-
/* Keep this last, we don't need it for the fast path */
struct wait_queue_head poll_wq;
struct io_restriction restrictions;
diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 5b80849fbb85..8ce36c5a37c4 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -303,7 +303,6 @@ static __cold struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
INIT_LIST_HEAD(&ctx->sqd_list);
INIT_LIST_HEAD(&ctx->cq_overflow_list);
INIT_LIST_HEAD(&ctx->io_buffers_cache);
- INIT_HLIST_HEAD(&ctx->io_buf_list);
io_alloc_cache_init(&ctx->rsrc_node_cache, IO_NODE_ALLOC_CACHE_MAX,
sizeof(struct io_rsrc_node));
io_alloc_cache_init(&ctx->apoll_cache, IO_ALLOC_CACHE_MAX,
@@ -2615,7 +2614,7 @@ static int io_cqring_wait(struct io_ring_ctx *ctx, int min_events,
return READ_ONCE(rings->cq.head) == READ_ONCE(rings->cq.tail) ? ret : 0;
}
-void io_mem_free(void *ptr)
+static void io_mem_free(void *ptr)
{
if (!ptr)
return;
@@ -2728,7 +2727,7 @@ static void io_rings_free(struct io_ring_ctx *ctx)
ctx->sq_sqes = NULL;
}
-void *io_mem_alloc(size_t size)
+static void *io_mem_alloc(size_t size)
{
gfp_t gfp = GFP_KERNEL_ACCOUNT | __GFP_ZERO | __GFP_NOWARN | __GFP_COMP;
void *ret;
@@ -2838,7 +2837,6 @@ static __cold void io_ring_ctx_free(struct io_ring_ctx *ctx)
ctx->mm_account = NULL;
}
io_rings_free(ctx);
- io_kbuf_mmap_list_free(ctx);
percpu_ref_exit(&ctx->refs);
free_uid(ctx->user);
@@ -3307,11 +3305,9 @@ static void *io_uring_validate_mmap_request(struct file *file,
loff_t pgoff, size_t sz)
{
struct io_ring_ctx *ctx = file->private_data;
- loff_t offset = pgoff << PAGE_SHIFT;
- struct page *page;
void *ptr;
- switch (offset & IORING_OFF_MMAP_MASK) {
+ switch ((pgoff << PAGE_SHIFT) & IORING_OFF_MMAP_MASK) {
case IORING_OFF_SQ_RING:
case IORING_OFF_CQ_RING:
/* Don't allow mmap if the ring was setup without it */
@@ -3325,23 +3321,13 @@ static void *io_uring_validate_mmap_request(struct file *file,
return ERR_PTR(-EINVAL);
ptr = ctx->sq_sqes;
break;
- case IORING_OFF_PBUF_RING: {
- unsigned int bgid;
-
- bgid = (offset & ~IORING_OFF_MMAP_MASK) >> IORING_OFF_PBUF_SHIFT;
- rcu_read_lock();
- ptr = io_pbuf_get_address(ctx, bgid);
- rcu_read_unlock();
- if (!ptr)
- return ERR_PTR(-EINVAL);
- break;
- }
+ case IORING_OFF_PBUF_RING:
+ return 0;
default:
return ERR_PTR(-EINVAL);
}
- page = virt_to_head_page(ptr);
- if (sz > page_size(page))
+ if (sz > page_size(virt_to_head_page(ptr)))
return ERR_PTR(-EINVAL);
return ptr;
@@ -3352,6 +3338,7 @@ static void *io_uring_validate_mmap_request(struct file *file,
static __cold int io_uring_mmap(struct file *file, struct vm_area_struct *vma)
{
size_t sz = vma->vm_end - vma->vm_start;
+ long offset = vma->vm_pgoff << PAGE_SHIFT;
unsigned long pfn;
void *ptr;
@@ -3359,6 +3346,9 @@ static __cold int io_uring_mmap(struct file *file, struct vm_area_struct *vma)
if (IS_ERR(ptr))
return PTR_ERR(ptr);
+ if ((offset & IORING_OFF_MMAP_MASK) == IORING_OFF_PBUF_RING)
+ return io_pbuf_mmap(file, vma);
+
pfn = virt_to_phys(ptr) >> PAGE_SHIFT;
return remap_pfn_range(vma, vma->vm_start, pfn, sz, vma->vm_page_prot);
}
diff --git a/io_uring/io_uring.h b/io_uring/io_uring.h
index bae8c1e937c1..050efc3e7973 100644
--- a/io_uring/io_uring.h
+++ b/io_uring/io_uring.h
@@ -108,9 +108,6 @@ bool __io_alloc_req_refill(struct io_ring_ctx *ctx);
bool io_match_task_safe(struct io_kiocb *head, struct task_struct *task,
bool cancel_all);
-void *io_mem_alloc(size_t size);
-void io_mem_free(void *ptr);
-
enum {
IO_EVENTFD_OP_SIGNAL_BIT,
IO_EVENTFD_OP_FREE_BIT,
diff --git a/io_uring/kbuf.c b/io_uring/kbuf.c
index 206f4d352e15..52210772da2f 100644
--- a/io_uring/kbuf.c
+++ b/io_uring/kbuf.c
@@ -32,25 +32,12 @@ struct io_provide_buf {
__u16 bid;
};
-struct io_buf_free {
- struct hlist_node list;
- void *mem;
- size_t size;
- int inuse;
-};
-
-static inline struct io_buffer_list *__io_buffer_get_list(struct io_ring_ctx *ctx,
- unsigned int bgid)
-{
- return xa_load(&ctx->io_bl_xa, bgid);
-}
-
static inline struct io_buffer_list *io_buffer_get_list(struct io_ring_ctx *ctx,
unsigned int bgid)
{
lockdep_assert_held(&ctx->uring_lock);
- return __io_buffer_get_list(ctx, bgid);
+ return xa_load(&ctx->io_bl_xa, bgid);
}
static int io_buffer_add_list(struct io_ring_ctx *ctx,
@@ -191,24 +178,6 @@ void __user *io_buffer_select(struct io_kiocb *req, size_t *len,
return ret;
}
-/*
- * Mark the given mapped range as free for reuse
- */
-static void io_kbuf_mark_free(struct io_ring_ctx *ctx, struct io_buffer_list *bl)
-{
- struct io_buf_free *ibf;
-
- hlist_for_each_entry(ibf, &ctx->io_buf_list, list) {
- if (bl->buf_ring == ibf->mem) {
- ibf->inuse = 0;
- return;
- }
- }
-
- /* can't happen... */
- WARN_ON_ONCE(1);
-}
-
static int __io_remove_buffers(struct io_ring_ctx *ctx,
struct io_buffer_list *bl, unsigned nbufs)
{
@@ -220,23 +189,20 @@ static int __io_remove_buffers(struct io_ring_ctx *ctx,
if (bl->is_buf_ring) {
i = bl->buf_ring->tail - bl->head;
- if (bl->is_mmap) {
- /*
- * io_kbuf_list_free() will free the page(s) at
- * ->release() time.
- */
- io_kbuf_mark_free(ctx, bl);
- bl->buf_ring = NULL;
- bl->is_mmap = 0;
- } else if (bl->buf_nr_pages) {
+ if (bl->buf_nr_pages) {
int j;
- for (j = 0; j < bl->buf_nr_pages; j++)
- unpin_user_page(bl->buf_pages[j]);
+ for (j = 0; j < bl->buf_nr_pages; j++) {
+ if (bl->is_mmap)
+ put_page(bl->buf_pages[j]);
+ else
+ unpin_user_page(bl->buf_pages[j]);
+ }
kvfree(bl->buf_pages);
vunmap(bl->buf_ring);
bl->buf_pages = NULL;
bl->buf_nr_pages = 0;
+ bl->is_mmap = 0;
}
/* make sure it's seen as empty */
INIT_LIST_HEAD(&bl->buf_list);
@@ -537,63 +503,48 @@ static int io_pin_pbuf_ring(struct io_uring_buf_reg *reg,
return ret;
}
-/*
- * See if we have a suitable region that we can reuse, rather than allocate
- * both a new io_buf_free and mem region again. We leave it on the list as
- * even a reused entry will need freeing at ring release.
- */
-static struct io_buf_free *io_lookup_buf_free_entry(struct io_ring_ctx *ctx,
- size_t ring_size)
+static int io_alloc_map_pages(struct io_buffer_list *bl, size_t ring_size)
{
- struct io_buf_free *ibf, *best = NULL;
- size_t best_dist;
-
- hlist_for_each_entry(ibf, &ctx->io_buf_list, list) {
- size_t dist;
-
- if (ibf->inuse || ibf->size < ring_size)
- continue;
- dist = ibf->size - ring_size;
- if (!best || dist < best_dist) {
- best = ibf;
- if (!dist)
- break;
- best_dist = dist;
- }
+ int i, nr_pages;
+
+ nr_pages = (ring_size + PAGE_SIZE - 1) >> PAGE_SHIFT;
+ bl->buf_pages = kvmalloc_array(nr_pages, sizeof(struct page *), GFP_KERNEL);
+ if (!bl->buf_pages)
+ return -ENOMEM;
+
+ for (i = 0; i < nr_pages; i++) {
+ bl->buf_pages[i] = alloc_page(GFP_KERNEL);
+ if (!bl->buf_pages[i])
+ goto out_free;
}
- return best;
+ bl->buf_ring = vmap(bl->buf_pages, nr_pages, VM_MAP, PAGE_KERNEL);
+ if (bl->buf_ring) {
+ bl->buf_nr_pages = nr_pages;
+ return 0;
+ }
+out_free:
+ while (i--)
+ put_page(bl->buf_pages[i]);
+ kvfree(bl->buf_pages);
+ bl->buf_pages = NULL;
+ bl->buf_nr_pages = 0;
+ return -ENOMEM;
}
static int io_alloc_pbuf_ring(struct io_ring_ctx *ctx,
struct io_uring_buf_reg *reg,
struct io_buffer_list *bl)
{
- struct io_buf_free *ibf;
size_t ring_size;
- void *ptr;
+ int ret;
ring_size = reg->ring_entries * sizeof(struct io_uring_buf_ring);
- /* Reuse existing entry, if we can */
- ibf = io_lookup_buf_free_entry(ctx, ring_size);
- if (!ibf) {
- ptr = io_mem_alloc(ring_size);
- if (IS_ERR(ptr))
- return PTR_ERR(ptr);
-
- /* Allocate and store deferred free entry */
- ibf = kmalloc(sizeof(*ibf), GFP_KERNEL_ACCOUNT);
- if (!ibf) {
- io_mem_free(ptr);
- return -ENOMEM;
- }
- ibf->mem = ptr;
- ibf->size = ring_size;
- hlist_add_head(&ibf->list, &ctx->io_buf_list);
- }
- ibf->inuse = 1;
- bl->buf_ring = ibf->mem;
+ ret = io_alloc_map_pages(bl, ring_size);
+ if (ret)
+ return ret;
+
bl->is_buf_ring = 1;
bl->is_mmap = 1;
return 0;
@@ -710,30 +661,43 @@ int io_register_pbuf_status(struct io_ring_ctx *ctx, void __user *arg)
return 0;
}
-void *io_pbuf_get_address(struct io_ring_ctx *ctx, unsigned long bgid)
+int io_pbuf_mmap(struct file *file, struct vm_area_struct *vma)
{
+ struct io_ring_ctx *ctx = file->private_data;
+ loff_t pgoff = vma->vm_pgoff << PAGE_SHIFT;
struct io_buffer_list *bl;
+ unsigned long npages;
+ int bgid, ret;
- bl = __io_buffer_get_list(ctx, bgid);
+ bgid = (pgoff & ~IORING_OFF_MMAP_MASK) >> IORING_OFF_PBUF_SHIFT;
- if (!bl || !bl->is_mmap)
- return NULL;
+ /*
+ * We have to be a bit careful here - we're inside mmap and cannot
+ * grab the uring_lock. This means the buffer_list could be
+ * simultaneously going away, if someone is trying to be sneaky.
+ * Look it up under rcu so we now it's not going away, and attempt
+ * to grab a reference to it. If the ref is already zero, then fail
+ * the mapping. If successful, we'll drop the reference at at the end.
+ * This may then safely free the buffer_list (and drop the pages) at
+ * that point, vm_insert_pages() would've already grabbed the
+ * necessary vma references.
+ */
+ ret = 0;
+ rcu_read_lock();
+ bl = xa_load(&ctx->io_bl_xa, bgid);
+ /* must be a mmap'able buffer ring and have pages */
+ if (bl && bl->is_mmap && bl->buf_nr_pages)
+ ret = atomic_inc_not_zero(&bl->refs);
+ rcu_read_unlock();
+
+ /* buffer list is invalid or being torn down, fail the mapping */
+ if (!ret)
+ return -EINVAL;
- return bl->buf_ring;
-}
+ vm_flags_set(vma, VM_DONTEXPAND);
-/*
- * Called at or after ->release(), free the mmap'ed buffers that we used
- * for memory mapped provided buffer rings.
- */
-void io_kbuf_mmap_list_free(struct io_ring_ctx *ctx)
-{
- struct io_buf_free *ibf;
- struct hlist_node *tmp;
-
- hlist_for_each_entry_safe(ibf, tmp, &ctx->io_buf_list, list) {
- hlist_del(&ibf->list);
- io_mem_free(ibf->mem);
- kfree(ibf);
- }
+ npages = bl->buf_nr_pages;
+ ret = vm_insert_pages(vma, vma->vm_start, bl->buf_pages, &npages);
+ io_put_bl(ctx, bl);
+ return ret;
}
diff --git a/io_uring/kbuf.h b/io_uring/kbuf.h
index 8b868a1744e2..0723a6ffe731 100644
--- a/io_uring/kbuf.h
+++ b/io_uring/kbuf.h
@@ -55,13 +55,11 @@ int io_register_pbuf_ring(struct io_ring_ctx *ctx, void __user *arg);
int io_unregister_pbuf_ring(struct io_ring_ctx *ctx, void __user *arg);
int io_register_pbuf_status(struct io_ring_ctx *ctx, void __user *arg);
-void io_kbuf_mmap_list_free(struct io_ring_ctx *ctx);
-
void __io_put_kbuf(struct io_kiocb *req, unsigned issue_flags);
bool io_kbuf_recycle_legacy(struct io_kiocb *req, unsigned issue_flags);
-void *io_pbuf_get_address(struct io_ring_ctx *ctx, unsigned long bgid);
+int io_pbuf_mmap(struct file *file, struct vm_area_struct *vma);
static inline bool io_kbuf_recycle_ring(struct io_kiocb *req)
{
--
2.43.0
