On Thu, Aug 14, 2025 at 07:54:09PM -0700, Nathan Chen via Devel wrote:
> Hi,
>
> This is a follow up to the second RFC patchset [0] for supporting multiple
> vSMMU instances and using iommufd to propagate DMA mappings to kernel for
> VM-assigned host devices in a qemu VM.
>
> This patchset implements support for specifying multiple <iommu> devices
> within the VM definition when smmuv3Dev IOMMU model is specified, and is
> tested with Shameer's latest qemu RFC for HW-accelerated vSMMU devices [1]
>
> Moreover, it adds a new 'iommufdId' attribute for hostdev devices to be
> associated with the iommufd object.
>
> For instance, specifying the iommufd object and associated hostdev in a
> VM definition with multiple IOMMUs, 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>
> <iommufdId>iommufd0</iommufdId>
> <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>
> <iommufdId>iommufd0</iommufdId>
> <address type='pci' domain='0x0000' bus='0x16' slot='0x00'
> function='0x0'/>
> </hostdev>
> <iommu model='smmuv3Dev' parentIdx='1' accel='on'/>
> <iommu model='smmuv3Dev' parentIdx='2' accel='on'/>
> </devices>
>
> This would get translated to a qemu command line with the arguments below.
> Note that libvirt will open the /dev/iommu and VFIO cdev, passing the
> associated fd number to qemu:
>
> -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"}'
> \
> -object '{"qom-type":"iommufd","id":"iommufd0","fd":"24"}' \
> -device
> '{"driver":"arm-smmuv3-accel","primary-bus":"pci.1","id":"smmuv3.0","accel":true}'
> \
> -device
> '{"driver":"arm-smmuv3-accel","primary-bus":"pci.2","id":"smmuv3.1","accel":true}'
> \
> -device
> '{"driver":"vfio-pci","host":"0009:01:00.0","id":"hostdev0","iommufd":"iommufd0","fd":"22","bus":"pci.21","addr":"0x0"}'
> \
> -device
> '{"driver":"vfio-pci","host":"0019:01:00.0","id":"hostdev1","iommufd":"iommufd0","fd":"25","bus":"pci.22","addr":"0x0"}'
> \
>
> Summary of changes:
> - Separated out commits for smmuv3Dev iommu model support and
> supporting multiple IOMMU definitions
> - Made iommufd only a hostdev attribute
> - Revised smmuv3Dev iommu model definition to reference the controller
> index instead of assigning it a BDF
> - Open iommufd FDs from libvirt backend without exposing FDs to XML users
> - Fixed iommufd path permissions
> - Matched qemu usage of Shameer's latest RFCv3
>
> This series is on Github:
> https://github.com/NathanChenNVIDIA/libvirt/tree/smmuv3Dev-iommufd-08-12-25
>
> Thanks,
> Nathan
>
> [0]
> https://lists.libvirt.org/archives/list/[email protected]/thread/EASBQHPCLPK5G3PF3DEU57G6CI4GSC74/
> [1]
> https://lore.kernel.org/qemu-devel/[email protected]/
>
> Signed-off-by: Nathan Chen <[email protected]>
>
>
> Nathan Chen (5):
> qemu: add IOMMU model smmuv3Dev
> conf: Support multiple smmuv3Dev IOMMU devices
> qemu: Implement support for associating iommufd to hostdev
> qemu: open iommufd FDs from libvirt backend
> qemu: Update Cgroup, namespace, and seclabel for qemu to access
> iommufd paths
>
> docs/formatdomain.rst | 22 ++-
> src/conf/domain_conf.c | 208 ++++++++++++++++++++++--
> src/conf/domain_conf.h | 13 +-
> src/conf/domain_validate.c | 58 +++++--
> src/conf/schemas/domaincommon.rng | 24 ++-
> src/libvirt_private.syms | 2 +
> src/qemu/qemu_alias.c | 15 +-
> src/qemu/qemu_cgroup.c | 61 +++++++
> src/qemu/qemu_cgroup.h | 1 +
> src/qemu/qemu_command.c | 261 ++++++++++++++++++++++--------
> src/qemu/qemu_command.h | 3 +-
> src/qemu/qemu_domain.c | 8 +
> src/qemu/qemu_domain.h | 7 +
> src/qemu/qemu_domain_address.c | 33 ++--
> src/qemu/qemu_driver.c | 8 +-
> src/qemu/qemu_hotplug.c | 2 +-
> src/qemu/qemu_namespace.c | 44 +++++
> src/qemu/qemu_postparse.c | 11 +-
> src/qemu/qemu_process.c | 232 ++++++++++++++++++++++++++
> src/qemu/qemu_validate.c | 18 ++-
> src/security/security_apparmor.c | 11 ++
> src/security/security_dac.c | 23 +++
> src/security/security_selinux.c | 24 +++
> src/util/virpci.c | 68 ++++++++
> src/util/virpci.h | 1 +
> 25 files changed, 1020 insertions(+), 138 deletions(-)
We could do with some changes to the test suite to provide sample XML
and CLI args for the iommufd XML schema.
With regards,
Daniel
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