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Differential D54959

virtio: Use bus_dma for ring and indirect buffer allocations
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Authored by sarah.walker2_arm.com on Jan 30 2026, 11:14 AM.
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cperciva
emaste
imp
jrtc27

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Reviewers
bryanv
andrew
Summary

While the majority of virtio platforms will be fully coherent, some may
require cache maintenance or other specific device memory handling (eg for
secure partitioning). Using bus_dma allows for these usecases.

The virtio buffers are marked as coherent; this should ensure that sync
calls are no-ops in the common cases.

Sponsored by: Arm Ltd

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rG FreeBSD src repository
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Build Status
Buildable 70963
Build 67846: arc lint + arc unit

Event Timeline

sarah.walker2_arm.com created this revision.Jan 30 2026, 11:14 AM
Herald added a subscriber: imp. · View Herald TranscriptJan 30 2026, 11:14 AM
sarah.walker2_arm.com requested review of this revision.Jan 30 2026, 11:14 AM
Harbormaster completed remote builds in B70227: Diff 170769.Jan 30 2026, 11:14 AM
sarah.walker2_arm.com added a child revision: D54960: virtio_blk: Use bus_dma for command/ack buffer allocations.Jan 30 2026, 11:14 AM
andrew added reviewers: bryanv, andrew.Mon, Feb 2, 5:42 PM
emaste added a subscriber: emaste.Tue, Feb 3, 5:23 PM
jrtc27 added a subscriber: jrtc27.Tue, Feb 3, 5:30 PM

Do we still need the mb()s? I would expect bus_dmamap_sync to suffice.

jrtc27 added a comment.Tue, Feb 3, 5:31 PM

virtio_blk calls bus_dma_tag_set_iommu on PowerPC; would that not be needed for these new tags?

br mentioned this in D55220: virtio: get a correct tag for IOMMU operation.Tue, Feb 10, 2:05 PM
sarah.walker2_arm.com updated this revision to Diff 171981.Mon, Feb 16, 3:36 PM

Remove superfluous mb() calls.

Harbormaster completed remote builds in B70704: Diff 171981.Mon, Feb 16, 3:36 PM
andrew added a subscriber: cperciva.Tue, Feb 17, 12:06 PM
In D54959#1259073, @jrtc27 wrote:

virtio_blk calls bus_dma_tag_set_iommu on PowerPC; would that not be needed for these new tags?

It looks like that was added in D37891 by @cperciva. Based on the commit message we could add it here, but can't test.

sarah.walker2_arm.com updated this revision to Diff 172614.Tue, Feb 24, 5:05 PM

Add iommu tag calls for PowerPC.

Harbormaster completed remote builds in B70963: Diff 172614.Tue, Feb 24, 5:05 PM
andrew accepted this revision.Tue, Feb 24, 5:05 PM
This revision is now accepted and ready to land.Tue, Feb 24, 5:05 PM

Revision Contents
Changeset List

PathSize
sys/
dev/
virtio/
27 lines
216 lines

Diff 172614

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sys/dev/virtio/virtio_ring.h

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sys/dev/virtio/virtqueue.c

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