On Wed, May 18, 2022 at 05:14:49PM -0700, Eric Biggers wrote:

On Wed, May 18, 2022 at 10:11:31AM -0700, Keith Busch wrote:

quoted

diff --git a/block/fops.c b/block/fops.c
index b9b83030e0df..d8537c29602f 100644
--- a/block/fops.c
+++ b/block/fops.c

@@ -54,8 +54,9 @@ static ssize_t __blkdev_direct_IO_simple(struct kiocb *iocb,
 	struct bio bio;
 	ssize_t ret;
 
-	if ((pos | iov_iter_alignment(iter)) &
-	    (bdev_logical_block_size(bdev) - 1))
+	if ((pos | iov_iter_count(iter)) & (bdev_logical_block_size(bdev) - 1))
+		return -EINVAL;
+	if (iov_iter_alignment(iter) & bdev_dma_alignment(bdev))
 		return -EINVAL;

The block layer makes a lot of assumptions that bios can be split at any bvec
boundary.  With this patch, bios whose length isn't a multiple of the logical
block size can be generated by splitting, which isn't valid.

How? This patch ensures every segment is block size aligned. We can always
split a bio in the middle of a bvec for any lower level hardware constraints,
and I'm not finding any splitting criteria that would try to break a bio on a
non-block aligned boundary.

Also some devices aren't compatible with logical blocks spanning bdevs at all.
dm-crypt errors out in this case, for example.

I'm sorry, but I am not understanding this.