[libvirt-users] multiple devices in the same iommu group in L1 guest

Laine Stump

2018-08-06 19:28:21 UTC

Post by Yalan Zhang
Hi,
I have a guest enabled vIOMMU, but on the guest there are several
devices in the same iommu group.
Could someone help to check if I missed something?
Thank you very much!
# virsh edit q
...
<os>
<type arch='x86_64' machine='pc-q35-rhel7.5.0'>hvm</type>
<loader readonly='yes' secure='yes'
type='pflash'>/usr/share/OVMF/OVMF_CODE.secboot.fd</loader>
<nvram>/var/lib/libvirt/qemu/nvram/q_VARS.fd</nvram>
</os>
...
<features>
...
<ioapic driver='qemu'/>
</features>
<cpu mode='host-passthrough' check='none'>
<feature policy='require' name='vmx'/>
</cpu>
...
<devices>
...
<controller type='pci' index='7' model='pcie-root-port'>
<model name='pcie-root-port'/>
<target chassis='7' port='0x15'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x02'
function='0x5'/>
</controller>
<interface type='network'>
<mac address='52:54:00:b9:ff:90'/>
<source network='default'/>
<model type='e1000'/>
<address type='pci' domain='0x0000' bus='0x07' slot='0x00'
function='0x0'/>
</interface>
<iommu model='intel'>
<driver intremap='on' caching_mode='on' iotlb='on'/>
</iommu>
</devices>
...
2. guest has 'intel_iommu=on' enabled in kernel cmdline, then reboot guest
# dmesg | grep -i DMAR
[ 0.000000] ACPI: DMAR 000000007d83f000 00050 (v01 BOCHS BXPCDMAR
00000001 BXPC 00000001)
[ 0.000000] DMAR: IOMMU enabled
[ 0.155178] DMAR: Host address width 39
[ 0.155180] DMAR: DRHD base: 0x000000fed90000 flags: 0x1
[ 0.155221] DMAR: dmar0: reg_base_addr fed90000 ver 1:0 cap
12008c22260286 ecap f00f5e
[ 0.155228] DMAR: ATSR flags: 0x1
[ 0.155231] DMAR-IR: IOAPIC id 0 under DRHD base 0xfed90000 IOMMU 0
[ 0.155232] DMAR-IR: Queued invalidation will be enabled to support
x2apic and Intr-remapping.
[ 0.156843] DMAR-IR: Enabled IRQ remapping in x2apic mode
[ 2.112369] DMAR: No RMRR found
[ 2.112505] DMAR: dmar0: Using Queued invalidation
[ 2.112671] DMAR: Prepare 0-16MiB unity mapping for LPC
[ 2.112820] DMAR: Setting identity map for device 0000:00:1f.0 [0x0 -
0xffffff]
[ 2.211577] DMAR: Intel(R) Virtualization Technology for Directed I/O
===> This is expected
# dmesg | grep -i iommu |grep device
[ 2.212267] iommu: Adding device 0000:00:00.0 to group 0
[ 2.212287] iommu: Adding device 0000:00:01.0 to group 1
[ 2.212372] iommu: Adding device 0000:00:02.0 to group 2
[ 2.212392] iommu: Adding device 0000:00:02.1 to group 2
[ 2.212411] iommu: Adding device 0000:00:02.2 to group 2
[ 2.212444] iommu: Adding device 0000:00:02.3 to group 2
[ 2.212464] iommu: Adding device 0000:00:02.4 to group 2
[ 2.212482] iommu: Adding device 0000:00:02.5 to group 2
[ 2.212520] iommu: Adding device 0000:00:1d.0 to group 3
[ 2.212533] iommu: Adding device 0000:00:1d.1 to group 3
[ 2.212541] iommu: Adding device 0000:00:1d.2 to group 3
[ 2.212550] iommu: Adding device 0000:00:1d.7 to group 3
[ 2.212567] iommu: Adding device 0000:00:1f.0 to group 4
[ 2.212576] iommu: Adding device 0000:00:1f.2 to group 4
[ 2.212585] iommu: Adding device 0000:00:1f.3 to group 4
[ 2.212599] iommu: Adding device 0000:01:00.0 to group 2
[ 2.212605] iommu: Adding device 0000:02:01.0 to group 2
[ 2.212621] iommu: Adding device 0000:04:00.0 to group 2
[ 2.212634] iommu: Adding device 0000:05:00.0 to group 2
[ 2.212646] iommu: Adding device 0000:06:00.0 to group 2
[ 2.212657] iommu: Adding device 0000:07:00.0 to group 2
====> several devices in the same iommu group
# virsh nodedev-dumpxml pci_0000_07_00_0
<device>
<name>pci_0000_07_00_0</name>
<path>/sys/devices/pci0000:00/0000:00:02.5/0000:07:00.0</path>
<parent>pci_0000_00_02_5</parent>
<driver>
<name>e1000</name>
</driver>
<capability type='pci'>
<domain>0</domain>
<bus>7</bus>
<slot>0</slot>
<function>0</function>
<product id='0x100e'>82540EM Gigabit Ethernet Controller</product>
<vendor id='0x8086'>Intel Corporation</vendor>
<iommuGroup number='2'>
<address domain='0x0000' bus='0x00' slot='0x02' function='0x0'/>
<address domain='0x0000' bus='0x00' slot='0x02' function='0x1'/>
<address domain='0x0000' bus='0x00' slot='0x02' function='0x2'/>
<address domain='0x0000' bus='0x00' slot='0x02' function='0x3'/>
<address domain='0x0000' bus='0x00' slot='0x02' function='0x4'/>
<address domain='0x0000' bus='0x00' slot='0x02' function='0x5'/>
<address domain='0x0000' bus='0x01' slot='0x00' function='0x0'/>
<address domain='0x0000' bus='0x02' slot='0x01' function='0x0'/>
<address domain='0x0000' bus='0x04' slot='0x00' function='0x0'/>
<address domain='0x0000' bus='0x05' slot='0x00' function='0x0'/>
<address domain='0x0000' bus='0x06' slot='0x00' function='0x0'/>
<address domain='0x0000' bus='0x07' slot='0x00' function='0x0'/>
</iommuGroup>

All devices plugged into the same slot on pcie-root are in the same
iommu group, and all devices are in the same iommu group as the
pcie-root-port they are plugged into. Since libvirt groups 8
pcie-root-ports onto a single pcie-root slot (to conserve the relatively
limited number of slots), all the devices plugged into those 8
pcie-root-ports are in the same iommu group.

This can be solved by putting the pcie-root-ports *of the devices you
want to assign to L2 guests* onto pcie-root slots by themselves, i.e.
instead of addressing it at 00:02.5, address it at 00:10.0 (and don't
put any other pcie-root-ports at 00:10.x).

I had thought there was an open BZ about this, but can't find one
anywhere. At first glance it would seem that, since the pcie-root-ports
and iommu controller are all emulated devices, it would be simple to
just report all the pcie-root-ports as being on different iommu groups
regardless of their placement on pcie-root, but I believe when this was
brought up doubt was expressed over whether or not qemu truly can
guarantee that the devices are fully isolated from each other.

Post by Yalan Zhang
</capability>
</device>
# cat hostdev.xml
<hostdev mode='subsystem' type='pci' managed='yes'>
<source>
<address domain='0x0000' bus='0x07' slot='0x00' function='0x0'/>
</source>
</hostdev>
# virsh attach-device rhel hostdev.xml
error: Failed to attach device from hostdev.xml
error: internal error: unable to execute QEMU command 'device_add': vfio
error: 0000:07:00.0: group 2 is not viable
-------
Best Regards,
Yalan Zhang
IRC: yalzhang
Internal phone: 8389413
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