[PATCH v3 09/10] io_uring/rsrc: extend buffer update

[Pavel Begunkov <asml.silence@gmail.com>]

We need to pass more information to buffer registration than we can fit
into a single struct iovec. This patch allows users to optionally pass
struct io_uring_regbuf_desc. Apart from having more space for future use
cases, it also introduces registration types.

Currently, the type can be either of IO_REGBUF_TYPE_UADDR, which mirrors
the iovec path, or IO_REGBUF_TYPE_EMPTY for leaving a buffer table slot
empty. The next patch introduces a dmabuf backed type, and can be useful
for other extensions like splicing a list of user addresses (i.e.
iovec[]), interoperability with zcrx, kernel allocated memory like was
brough up by Cristoph. Note, the type only represents a registration
option, which is distinct from how io_uring internally stores it.

The flags field is not used yet but always useful to have, e.g. we can
encode read-only / write-only restrictions using it.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 include/uapi/linux/io_uring.h | 27 +++++++++++++-
 io_uring/rsrc.c               | 69 ++++++++++++++++++++++-------------
 2 files changed, 69 insertions(+), 27 deletions(-)

diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 17ac1b785440..05c3fd078767 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -790,13 +790,38 @@ struct io_uring_rsrc_update {
 
 struct io_uring_rsrc_update2 {
 	__u32 offset;
-	__u32 resv;
+	__u32 flags;
 	__aligned_u64 data;
 	__aligned_u64 tags;
 	__u32 nr;
 	__u32 resv2;
 };
 
+/* struct io_uring_rsrc_update2::flags */
+enum io_uring_rsrc_reg_flags {
+	/*
+	 * Use the extended descriptor format for buffer updates,
+	 * see struct io_uring_regbuf_desc
+	 */
+	IORING_RSRC_UPDATE_EXTENDED		= 1U << 1,
+};
+
+/* Buffer registration type, passed in struct io_uring_regbuf_desc::type */
+enum io_uring_regbuf_type {
+	IO_REGBUF_TYPE_EMPTY,
+	IO_REGBUF_TYPE_UADDR,
+
+	__IO_REGBUF_TYPE_MAX,
+};
+
+struct io_uring_regbuf_desc {
+	__u32 type; /* enum io_uring_regbuf_type */
+	__u32 flags;
+	__u64 size;
+	__u64 uaddr;
+	__u64 __resv[7];
+};
+
 /* Skip updating fd indexes set to this value in the fd table */
 #define IORING_REGISTER_FILES_SKIP	(-2)
 
diff --git a/io_uring/rsrc.c b/io_uring/rsrc.c
index ba00238941ed..f8696b01cb54 100644
--- a/io_uring/rsrc.c
+++ b/io_uring/rsrc.c
@@ -27,11 +27,6 @@ struct io_rsrc_update {
 	u32				offset;
 };
 
-struct io_uring_regbuf_desc {
-	__u64 uaddr;
-	__u64 size;
-};
-
 static struct io_rsrc_node *io_sqe_buffer_register(struct io_ring_ctx *ctx,
 					struct io_uring_regbuf_desc *desc,
 					struct page **last_hpage);
@@ -46,9 +41,12 @@ static void io_iov_to_regbuf_desc(const struct iovec *iov,
 				  struct io_uring_regbuf_desc *desc)
 {
 	*desc = (struct io_uring_regbuf_desc) {
+		.type = IO_REGBUF_TYPE_UADDR,
 		.uaddr = (u64)iov->iov_base,
 		.size = iov->iov_len,
 	};
+	if (!desc->uaddr)
+		desc->type = IO_REGBUF_TYPE_EMPTY;
 }
 
 int __io_account_mem(struct user_struct *user, unsigned long nr_pages)
@@ -236,6 +234,8 @@ static int __io_sqe_files_update(struct io_ring_ctx *ctx,
 		return -ENXIO;
 	if (up->offset + nr_args > ctx->file_table.data.nr)
 		return -EINVAL;
+	if (up->flags)
+		return -EINVAL;
 
 	for (done = 0; done < nr_args; done++) {
 		u64 tag = 0;
@@ -292,10 +292,9 @@ static int __io_sqe_buffers_update(struct io_ring_ctx *ctx,
 				   struct io_uring_rsrc_update2 *up,
 				   unsigned int nr_args)
 {
+	bool extended = up->flags & IORING_RSRC_UPDATE_EXTENDED;
 	u64 __user *tags = u64_to_user_ptr(up->tags);
-	struct iovec fast_iov, *iov;
 	struct page *last_hpage = NULL;
-	struct iovec __user *uvec;
 	u64 user_data = up->data;
 	__u32 done;
 	int i, err;
@@ -304,29 +303,49 @@ static int __io_sqe_buffers_update(struct io_ring_ctx *ctx,
 		return -ENXIO;
 	if (up->offset + nr_args > ctx->buf_table.nr)
 		return -EINVAL;
+	if (up->flags & ~IORING_RSRC_UPDATE_EXTENDED)
+		return -EINVAL;
 
 	for (done = 0; done < nr_args; done++) {
 		struct io_uring_regbuf_desc desc;
 		struct io_rsrc_node *node;
 		u64 tag = 0;
 
-		uvec = u64_to_user_ptr(user_data);
-		iov = iovec_from_user(uvec, 1, 1, &fast_iov, io_is_compat(ctx));
-		if (IS_ERR(iov)) {
-			err = PTR_ERR(iov);
-			break;
-		}
 		if (tags && copy_from_user(&tag, &tags[done], sizeof(tag))) {
 			err = -EFAULT;
 			break;
 		}
 
-		io_iov_to_regbuf_desc(iov, &desc);
+		if (extended) {
+			if (copy_from_user(&desc, u64_to_user_ptr(user_data),
+					   sizeof(desc))) {
+				err = -EFAULT;
+				break;
+			}
+			user_data += sizeof(desc);
+		} else {
+			struct iovec __user *uvec = u64_to_user_ptr(user_data);
+			struct iovec fast_iov, *iov;
+
+			if (io_is_compat(ctx))
+				user_data += sizeof(struct compat_iovec);
+			else
+				user_data += sizeof(struct iovec);
+
+			iov = iovec_from_user(uvec, 1, 1, &fast_iov, io_is_compat(ctx));
+			if (IS_ERR(iov)) {
+				err = PTR_ERR(iov);
+				break;
+			}
+			io_iov_to_regbuf_desc(iov, &desc);
+		}
+
 		node = io_sqe_buffer_register(ctx, &desc, &last_hpage);
 		if (IS_ERR(node)) {
 			err = PTR_ERR(node);
 			break;
 		}
+
 		if (tag) {
 			if (!node) {
 				err = -EINVAL;
@@ -337,10 +356,6 @@ static int __io_sqe_buffers_update(struct io_ring_ctx *ctx,
 		i = array_index_nospec(up->offset + done, ctx->buf_table.nr);
 		io_reset_rsrc_node(ctx, &ctx->buf_table, i);
 		ctx->buf_table.nodes[i] = node;
-		if (io_is_compat(ctx))
-			user_data += sizeof(struct compat_iovec);
-		else
-			user_data += sizeof(struct iovec);
 	}
 	return done ? done : err;
 }
@@ -375,7 +390,7 @@ int io_register_files_update(struct io_ring_ctx *ctx, void __user *arg,
 	memset(&up, 0, sizeof(up));
 	if (copy_from_user(&up, arg, sizeof(struct io_uring_rsrc_update)))
 		return -EFAULT;
-	if (up.resv || up.resv2)
+	if (up.resv2)
 		return -EINVAL;
 	return __io_register_rsrc_update(ctx, IORING_RSRC_FILE, &up, nr_args);
 }
@@ -389,7 +404,7 @@ int io_register_rsrc_update(struct io_ring_ctx *ctx, void __user *arg,
 		return -EINVAL;
 	if (copy_from_user(&up, arg, sizeof(up)))
 		return -EFAULT;
-	if (!up.nr || up.resv || up.resv2)
+	if (!up.nr || up.resv2)
 		return -EINVAL;
 	return __io_register_rsrc_update(ctx, type, &up, up.nr);
 }
@@ -489,12 +504,9 @@ int io_files_update(struct io_kiocb *req, unsigned int issue_flags)
 	struct io_uring_rsrc_update2 up2;
 	int ret;
 
+	memset(&up2, 0, sizeof(up2));
 	up2.offset = up->offset;
 	up2.data = up->arg;
-	up2.nr = 0;
-	up2.tags = 0;
-	up2.resv = 0;
-	up2.resv2 = 0;
 
 	if (up->offset == IORING_FILE_INDEX_ALLOC) {
 		ret = io_files_update_with_index_alloc(req, issue_flags);
@@ -791,8 +803,13 @@ static struct io_rsrc_node *io_sqe_buffer_register(struct io_ring_ctx *ctx,
 	struct io_imu_folio_data data;
 	bool coalesced = false;
 
-	if (!uaddr) {
-		if (size)
+	if (desc->type >= __IO_REGBUF_TYPE_MAX)
+		return ERR_PTR(-EINVAL);
+	if (!mem_is_zero(&desc->__resv, sizeof(desc->__resv)))
+		return ERR_PTR(-EINVAL);
+
+	if (desc->type == IO_REGBUF_TYPE_EMPTY) {
+		if (uaddr || size)
 			return ERR_PTR(-EFAULT);
 		/* remove the buffer without installing a new one */
 		return NULL;
-- 
2.53.0