[PATCH 3/4] io_uring: make loop_rw_iter() use original user supplied pointers

[Jens Axboe <axboe@kernel.dk>]

We jump through a hoop for fixed buffers, where we first map these to
a bvec(), then kmap() the bvec to obtain the pointer we copy to/from.
This was always a bit ugly, and with the set_fs changes, it ends up
being practically problematic as well.

There's no need to jump through these hoops, just use the original user
pointers and length for the non iter based read/write.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/io_uring.c | 21 +++++++++------------
 1 file changed, 9 insertions(+), 12 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 45320458a5f9..70ce36612e12 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -3115,9 +3115,10 @@ static inline loff_t *io_kiocb_ppos(struct kiocb *kiocb)
  * For files that don't have ->read_iter() and ->write_iter(), handle them
  * by looping over ->read() or ->write() manually.
  */
-static ssize_t loop_rw_iter(int rw, struct file *file, struct kiocb *kiocb,
-			   struct iov_iter *iter)
+static ssize_t loop_rw_iter(int rw, struct io_kiocb *req, struct iov_iter *iter)
 {
+	struct kiocb *kiocb = &req->rw.kiocb;
+	struct file *file = req->file;
 	ssize_t ret = 0;
 
 	/*
@@ -3137,11 +3138,8 @@ static ssize_t loop_rw_iter(int rw, struct file *file, struct kiocb *kiocb,
 		if (!iov_iter_is_bvec(iter)) {
 			iovec = iov_iter_iovec(iter);
 		} else {
-			/* fixed buffers import bvec */
-			iovec.iov_base = kmap(iter->bvec->bv_page)
-						+ iter->iov_offset;
-			iovec.iov_len = min(iter->count,
-					iter->bvec->bv_len - iter->iov_offset);
+			iovec.iov_base = (void __user *) req->rw.addr;
+			iovec.iov_len = req->rw.len;
 		}
 
 		if (rw == READ) {
@@ -3152,9 +3150,6 @@ static ssize_t loop_rw_iter(int rw, struct file *file, struct kiocb *kiocb,
 					       iovec.iov_len, io_kiocb_ppos(kiocb));
 		}
 
-		if (iov_iter_is_bvec(iter))
-			kunmap(iter->bvec->bv_page);
-
 		if (nr < 0) {
 			if (!ret)
 				ret = nr;
@@ -3163,6 +3158,8 @@ static ssize_t loop_rw_iter(int rw, struct file *file, struct kiocb *kiocb,
 		ret += nr;
 		if (nr != iovec.iov_len)
 			break;
+		req->rw.len -= nr;
+		req->rw.addr += nr;
 		iov_iter_advance(iter, nr);
 	}
 
@@ -3352,7 +3349,7 @@ static int io_iter_do_read(struct io_kiocb *req, struct iov_iter *iter)
 	if (req->file->f_op->read_iter)
 		return call_read_iter(req->file, &req->rw.kiocb, iter);
 	else if (req->file->f_op->read)
-		return loop_rw_iter(READ, req->file, &req->rw.kiocb, iter);
+		return loop_rw_iter(READ, req, iter);
 	else
 		return -EINVAL;
 }
@@ -3543,7 +3540,7 @@ static int io_write(struct io_kiocb *req, bool force_nonblock,
 	if (req->file->f_op->write_iter)
 		ret2 = call_write_iter(req->file, kiocb, iter);
 	else if (req->file->f_op->write)
-		ret2 = loop_rw_iter(WRITE, req->file, kiocb, iter);
+		ret2 = loop_rw_iter(WRITE, req, iter);
 	else
 		ret2 = -EINVAL;
 
-- 
2.29.0