[PATCH v3 2/8] io_uring/kbuf: support kernel-managed buffer rings in buffer selection

[Joanne Koong <joannelkoong@gmail.com>]

Allow kernel-managed buffers to be selected. This requires modifying the
io_br_sel struct to separate the fields for address and val, since a
kernel address cannot be distinguished from a negative val when error
checking.

Auto-commit any selected kernel-managed buffer.

Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
---
 include/linux/io_uring_types.h |  8 ++++----
 io_uring/kbuf.c                | 16 ++++++++++++----
 2 files changed, 16 insertions(+), 8 deletions(-)

diff --git a/include/linux/io_uring_types.h b/include/linux/io_uring_types.h
index 3e4a82a6f817..36cc2e0346d9 100644
--- a/include/linux/io_uring_types.h
+++ b/include/linux/io_uring_types.h
@@ -93,13 +93,13 @@ struct io_mapped_region {
  */
 struct io_br_sel {
 	struct io_buffer_list *buf_list;
-	/*
-	 * Some selection parts return the user address, others return an error.
-	 */
 	union {
+		/* for classic/ring provided buffers */
 		void __user *addr;
-		ssize_t val;
+		/* for kernel-managed buffers */
+		void *kaddr;
 	};
+	ssize_t val;
 };
 
 
diff --git a/io_uring/kbuf.c b/io_uring/kbuf.c
index 0e42c8f602e1..13b80c667881 100644
--- a/io_uring/kbuf.c
+++ b/io_uring/kbuf.c
@@ -155,7 +155,8 @@ static int io_provided_buffers_select(struct io_kiocb *req, size_t *len,
 	return 1;
 }
 
-static bool io_should_commit(struct io_kiocb *req, unsigned int issue_flags)
+static bool io_should_commit(struct io_kiocb *req, struct io_buffer_list *bl,
+			     unsigned int issue_flags)
 {
 	/*
 	* If we came in unlocked, we have no choice but to consume the
@@ -170,7 +171,11 @@ static bool io_should_commit(struct io_kiocb *req, unsigned int issue_flags)
 	if (issue_flags & IO_URING_F_UNLOCKED)
 		return true;
 
-	/* uring_cmd commits kbuf upfront, no need to auto-commit */
+	/* kernel-managed buffers are auto-committed */
+	if (bl->flags & IOBL_KERNEL_MANAGED)
+		return true;
+
+	/* multishot uring_cmd commits kbuf upfront, no need to auto-commit */
 	if (!io_file_can_poll(req) && !io_is_uring_cmd(req))
 		return true;
 	return false;
@@ -200,9 +205,12 @@ static struct io_br_sel io_ring_buffer_select(struct io_kiocb *req, size_t *len,
 	req->flags |= REQ_F_BUFFER_RING | REQ_F_BUFFERS_COMMIT;
 	req->buf_index = READ_ONCE(buf->bid);
 	sel.buf_list = bl;
-	sel.addr = u64_to_user_ptr(READ_ONCE(buf->addr));
+	if (bl->flags & IOBL_KERNEL_MANAGED)
+		sel.kaddr = (void *)(uintptr_t)READ_ONCE(buf->addr);
+	else
+		sel.addr = u64_to_user_ptr(READ_ONCE(buf->addr));
 
-	if (io_should_commit(req, issue_flags)) {
+	if (io_should_commit(req, bl, issue_flags)) {
 		io_kbuf_commit(req, sel.buf_list, *len, 1);
 		sel.buf_list = NULL;
 	}
-- 
2.47.3