[PATCH v2] block: only fail dma-buf bios that need block layer PI

[Kyle Bader <kbader@redhat.com>]

From: Kyle Bader <kbader@ibm.com>

All dma-buf (P2P) I/O to a device with integrity data is rejected
today, at registration and in blk_mq_submit_bio(). Only a bio for which
the block layer generates or verifies PI needs that. The block layer
then walks the bio_vecs, and a dma-buf bio has none.

Reject only those bios, and remove the check at registration. Then a
submitter that attaches its own PI, for example with
IORING_RW_ATTR_FLAG_PI, can do dma-buf I/O to such a device.

Link: https://lore.kernel.org/all/bbb87d6b-b7a3-487a-8be4-27f3f9ce4a1b@samsung.com/
Assisted-by: LLM
Reviewed-by: Anuj Gupta <anuj20.g@samsung.com>
Signed-off-by: Kyle Bader <kbader@ibm.com>
---
v2: a shorter commit message (Christoph), and Anuj's Reviewed-by. The
code is the same as in v1, so the tests of v1 still apply.

v1: https://lore.kernel.org/all/20261028181412.1919506-1-kbader@redhat.com/

 block/blk-mq.c | 9 ++++++++-
 block/fops.c   | 2 --
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 7fff1305b..3fc9fdeb3 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -3138,8 +3138,15 @@ void blk_mq_submit_bio(struct bio *bio)
 		goto queue_exit;
 	}
 
+	/*
+	 * The block layer cannot generate or verify PI for a dma-buf bio, as
+	 * that walks the data pages.  Only fail the bio if it needs that, not
+	 * if the submitter attached its own integrity payload or if PI
+	 * generation or verification is turned off for the device.
+	 */
 	if (unlikely(op_is_dmabuf(bio->bi_opf) &&
-		     bdev_has_integrity_csum(bio->bi_bdev))) {
+		     bdev_has_integrity_csum(bio->bi_bdev) &&
+		     (bio_integrity_action(bio) & BI_ACT_CHECK))) {
 		bio_endio_status(bio, BLK_STS_NOTSUPP);
 		goto queue_exit;
 	}
diff --git a/block/fops.c b/block/fops.c
index 01bc8afe3..5c8024011 100644
--- a/block/fops.c
+++ b/block/fops.c
@@ -947,8 +947,6 @@ static int blkdev_init_dma_buf_io_ctx(struct file *file,
 		return -EINVAL;
 	if (!disk->fops->init_dma_buf_io_ctx)
 		return -EOPNOTSUPP;
-	if (bdev_has_integrity_csum(bdev))
-		return -EOPNOTSUPP;
 	return disk->fops->init_dma_buf_io_ctx(bdev, ctx);
 }
 

base-commit: 45b716456dd99488a0cef58482120dc0474aa696
-- 
2.56.0