[RFC PATCH v2 0/2] qemu: Support vCMDQ

11 Mar 2026

      Hi,

This is a follow up to the previous RFC patchset [0] for supporting
Tegra241 vCMDQ.

This patchset is tested with Shameer's v3 qemu series [1] for
vCMDQ support. The accelerated SMMUv3 series for qemu and Libvirt [2]
are pre-requisites for vCMDQ support, as accelerated SMMUv3 must be
enabled alongside vCMDQ.

A new 'cmdqv' <iommu> driver attribute is introduced to toggle enabling 
vCMDQ support. For instance, specifying hostdevs associated with
multiple accelerated SMMUs + CMDQV enabled, configured to be routed to
pcie-expander-bus controllers in a way where VFIO device to SMMUv3
associations are matched with the host:

  <devices>
...
    <controller type='pci' index='1' model='pcie-expander-bus'>
      <model name='pxb-pcie'/>
      <target busNr='252'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x0'/>
    </controller>
    <controller type='pci' index='2' model='pcie-expander-bus'>
      <model name='pxb-pcie'/>
      <target busNr='248'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0'/>
    </controller>
...
    <controller type='pci' index='21' model='pcie-root-port'>
      <model name='pcie-root-port'/>
      <target chassis='21' port='0x0'/>
      <address type='pci' domain='0x0000' bus='0x01' slot='0x00' function='0x0'/>
    </controller>
    <controller type='pci' index='22' model='pcie-root-port'>
      <model name='pcie-root-port'/>
      <target chassis='22' port='0xa8'/>
      <address type='pci' domain='0x0000' bus='0x02' slot='0x00' function='0x0'/>
    </controller>
...
    <hostdev mode='subsystem' type='pci' managed='no'>
      <source>
        <address domain='0x0009' bus='0x01' slot='0x00' function='0x0'/>
      </source>
      <address type='pci' domain='0x0000' bus='0x15' slot='0x00' function='0x0'/>
    </hostdev>
    <hostdev mode='subsystem' type='pci' managed='no'>
      <source>
        <address domain='0x0019' bus='0x01' slot='0x00' function='0x0'/>
      </source>
      <address type='pci' domain='0x0000' bus='0x16' slot='0x00' function='0x0'/>
    </hostdev>
    <iommu model='smmuv3'>
      <driver pciBus='1' accel='on' ats='on' ril='on' ssidSize='20' oas='44' cmdqv='on'/>
    </iommu>
    <iommu model='smmuv3'>
      <driver pciBus='2' accel='on' ats='on' ril='on' ssidSize='20' oas='44' cmdqv='on'/>
    </iommu>
  </devices>

This would get translated to a qemu command line with the arguments
below:

 -device '{"driver":"pxb-pcie","bus_nr":252,"id":"pci.1","bus":"pcie.0","addr":"0x1"}' \
 -device '{"driver":"pxb-pcie","bus_nr":248,"id":"pci.2","bus":"pcie.0","addr":"0x2"}' \
 -device '{"driver":"pcie-root-port","port":0,"chassis":21,"id":"pci.21","bus":"pci.1","addr":"0x0"}' \
 -device '{"driver":"pcie-root-port","port":168,"chassis":22,"id":"pci.22","bus":"pci.2","addr":"0x0"}' \
 -device '{"driver":"arm-smmuv3","primary-bus":"pci.1","id":"iommu0","accel":true,"ats":true,"cmdqv":"on","ril":true,"pasid":true,"oas":44}' \
 -device '{"driver":"arm-smmuv3","primary-bus":"pci.2","id":"iommu1","accel":true,"ats":true,"cmdqv":"on","ril":true,"pasid":true,"oas":44}' \
 -device '{"driver":"vfio-pci","host":"0009:01:00.0","id":"hostdev0","bus":"pci.21","addr":"0x0"}' \
 -device '{"driver":"vfio-pci","host":"0019:01:00.0","id":"hostdev1","bus":"pci.22","addr":"0x0"}' \

This series is on Github:
https://github.com/NathanChenNVIDIA/libvirt/tree/cmdqv-03-26/

Thanks,
Nathan

Changes from v1:
- Remove 'identifier' attribute for SMMUv3
- Change QEMU command line property from 'tegra241-cmdqv' to 'cmdqv'
- Support QEMU OnOffAuto CMDQV property instead of expecting a bool

[0] https://lists.libvirt.org/archives/list/devel@lists.libvirt.org/thread/NHVKF...
[1] https://lore.kernel.org/all/20260226105056.897-1-skolothumtho@nvidia.com/
[2] https://lists.libvirt.org/archives/list/devel@lists.libvirt.org/thread/5GG76...

Nathan Chen (2):
  qemu: Support NVIDIA Tegra241 CMDQV for SMMUv3
  tests: qemuxmlconfdata: provide cmdqv sample XML and CLI args

 docs/formatdomain.rst                         |  6 ++
 src/conf/domain_conf.c                        | 15 ++++
 src/conf/domain_conf.h                        |  1 +
 src/conf/domain_validate.c                    |  5 +-
 src/conf/schemas/domaincommon.rng             |  5 ++
 src/qemu/qemu_command.c                       |  1 +
 ...u-smmuv3-pci-bus-cmdqv.aarch64-latest.args | 45 +++++++++++
 ...mu-smmuv3-pci-bus-cmdqv.aarch64-latest.xml | 76 +++++++++++++++++++
 .../iommu-smmuv3-pci-bus-cmdqv.xml            | 66 ++++++++++++++++
 tests/qemuxmlconftest.c                       |  1 +
 10 files changed, 220 insertions(+), 1 deletion(-)
 create mode 100644 tests/qemuxmlconfdata/iommu-smmuv3-pci-bus-cmdqv.aarch64-latest.args
 create mode 100644 tests/qemuxmlconfdata/iommu-smmuv3-pci-bus-cmdqv.aarch64-latest.xml
 create mode 100644 tests/qemuxmlconfdata/iommu-smmuv3-pci-bus-cmdqv.xml

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2.43.0