[PATCH] block: require LBA dma_alignment when using PI

[PATCH] block: require LBA dma_alignment when using PI

[Christoph Hellwig]

The block layer PI generation / verification code expects the bio_vecs
to have at least LBA size (or more correctly integrity internal)
granularity.  With the direct I/O alignment relaxation in 2022, user
space can now feed bios with less alignment than that, leading to
scribbling outside the PI buffers.  Apparently this wasn't noticed so far
because none of the tests generate such buffers, but since 851c4c96db00
("xfs: implement XFS_IOC_DIOINFO in terms of vfs_getattr"), xfstests
generic/013 by default generates such I/O now that the relaxed alignment
is advertised by the XFS_IOC_DIOINFO ioctl.

Fix this by increasing the required alignment when using PI, although
handling arbitrary alignment in the long run would be even nicer.

Fixes: bf8d08532bc1 ("iomap: add support for dma aligned direct-io")
Fixes: b1a000d3b8ec ("block: relax direct io memory alignment")
Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 block/blk-settings.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/block/blk-settings.c b/block/blk-settings.c
index 54cffaae4df4..d74b13ec8e54 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -184,6 +184,16 @@ static int blk_validate_integrity_limits(struct queue_limits *lim)
 	if (!bi->interval_exp)
 		bi->interval_exp = ilog2(lim->logical_block_size);
 
+	/*
+	 * The PI generation / validation helpers do not expect intervals to
+	 * straddle multiple bio_vecs.  Enforce alignment so that those are
+	 * never generated, and that each buffer is aligned as expected.
+	 */
+	if (bi->csum_type) {
+		lim->dma_alignment = max(lim->dma_alignment,
+					(1U << bi->interval_exp) - 1);
+	}
+
 	return 0;
 }
 
-- 
2.47.3

Re: [PATCH] block: require LBA dma_alignment when using PI

[Keith Busch]

On Wed, Oct 22, 2025 at 10:33:31AM +0200, Christoph Hellwig wrote:
> The block layer PI generation / verification code expects the bio_vecs
> to have at least LBA size (or more correctly integrity internal)
> granularity.  With the direct I/O alignment relaxation in 2022, user
> space can now feed bios with less alignment than that, leading to
> scribbling outside the PI buffers.  Apparently this wasn't noticed so far
> because none of the tests generate such buffers, but since 851c4c96db00
> ("xfs: implement XFS_IOC_DIOINFO in terms of vfs_getattr"), xfstests
> generic/013 by default generates such I/O now that the relaxed alignment
> is advertised by the XFS_IOC_DIOINFO ioctl.
> 
> Fix this by increasing the required alignment when using PI, although
> handling arbitrary alignment in the long run would be even nicer.
> 
> Fixes: bf8d08532bc1 ("iomap: add support for dma aligned direct-io")
> Fixes: b1a000d3b8ec ("block: relax direct io memory alignment")

Wow! Looks good for now and stable. I agree handling block data across
discontiguous segments is a good plan for after this.

Reviewed-by: Keith Busch <kbusch@kernel.org>

Re: [PATCH] block: require LBA dma_alignment when using PI

[Martin K. Petersen]

Christoph,

> The block layer PI generation / verification code expects the bio_vecs
> to have at least LBA size (or more correctly integrity internal)
> granularity. With the direct I/O alignment relaxation in 2022, user
> space can now feed bios with less alignment than that, leading to
> scribbling outside the PI buffers. Apparently this wasn't noticed so
> far because none of the tests generate such buffers, but since
> 851c4c96db00 ("xfs: implement XFS_IOC_DIOINFO in terms of
> vfs_getattr"), xfstests generic/013 by default generates such I/O now
> that the relaxed alignment is advertised by the XFS_IOC_DIOINFO ioctl.
>
> Fix this by increasing the required alignment when using PI, although
> handling arbitrary alignment in the long run would be even nicer.

Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>

-- 
Martin K. Petersen

Re: [PATCH] block: require LBA dma_alignment when using PI

[Jens Axboe]

On Wed, 22 Oct 2025 10:33:31 +0200, Christoph Hellwig wrote:
> The block layer PI generation / verification code expects the bio_vecs
> to have at least LBA size (or more correctly integrity internal)
> granularity.  With the direct I/O alignment relaxation in 2022, user
> space can now feed bios with less alignment than that, leading to
> scribbling outside the PI buffers.  Apparently this wasn't noticed so far
> because none of the tests generate such buffers, but since 851c4c96db00
> ("xfs: implement XFS_IOC_DIOINFO in terms of vfs_getattr"), xfstests
> generic/013 by default generates such I/O now that the relaxed alignment
> is advertised by the XFS_IOC_DIOINFO ioctl.
> 
> [...]

Applied, thanks!

[1/1] block: require LBA dma_alignment when using PI
      commit: 4c8cf6bd28d6fea23819f082ddc8063fd6fa963a

Best regards,
-- 
Jens Axboe