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virtio-blk: Don't use MAX_DISCARD_SEGMENTS if max_discard_seg is zero

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Currently the value of max_discard_segment will be set to
MAX_DISCARD_SEGMENTS (256) with no basis in hardware if device
set 0 to max_discard_seg in configuration space. It's incorrect
since the device might not be able to handle such large descriptors.
To fix it, let's follow max_segments restrictions in this case.

Fixes: 1f23816b8e ("virtio_blk: add discard and write zeroes support")
Signed-off-by: Xie Yongji <xieyongji@bytedance.com>
Link: https://lore.kernel.org/r/20220304100058.116-1-xieyongji@bytedance.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
This commit is contained in:
Xie Yongji 2022-03-04 18:00:57 +08:00 committed by Michael S. Tsirkin
parent e2ae38cf3d
commit dacc73ed0b
1 changed files with 8 additions and 2 deletions
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10
drivers/block/virtio_blk.c
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@ -925,9 +925,15 @@ static int virtblk_probe(struct virtio_device *vdev)
virtio_cread(vdev, struct virtio_blk_config, max_discard_seg,
&v);
/*
* max_discard_seg == 0 is out of spec but we always
* handled it.
*/
if (!v)
v = sg_elems - 2;
blk_queue_max_discard_segments(q,
min_not_zero(v,
MAX_DISCARD_SEGMENTS));
min(v, MAX_DISCARD_SEGMENTS));
blk_queue_flag_set(QUEUE_FLAG_DISCARD, q);
}