Hi all,
I am trying to enable PCI-e device pass-through mode with KVM, since
Juno-r2 board has PCI-e bus so I firstly try to use vfio to
passthrough the network card on PCI-e bus.
According to Juno-r2 board TRM [1], there has a CoreLink MMU-401 (SMMU)
between PCI-e devices and CCI bus; IIUC, PCI-e device and the SMMU can
be used for vfio for address isolation and from hardware pespective it
is sufficient for support pass-through mode.
I followed Eric's blog [2] for 'VFIO-PCI driver binding', so I
executed blow commands on Juno-r2 board:
echo vfio-pci > /sys/bus/pci/devices/0000\:08\:00.0/driver_override
echo 0000:08:00.0 > /sys/bus/pci/drivers/sky2/unbind
echo 0000:08:00.0 > /sys/bus/pci/drivers_probe
But at the last command for vifo probing, it reports failure as below:
[ 21.553889] sky2 0000:08:00.0 enp8s0: disabling interface
[ 21.616720] vfio-pci: probe of 0000:08:00.0 failed with error -22
I looked into for the code, though 'dev->bus->iommu_ops' points to the
data structure 'arm_smmu_ops', but 'dev->iommu_group' is NULL thus the
probe function returns failure with below flow:
vfio_pci_probe()
`-> vfio_iommu_group_get()
`-> iommu_group_get()
`-> return NULL;
Alternatively, if enable the kconfig CONFIG_VFIO_NOIOMMU & set global
variable 'noiommu' = true, the probe function still returns error; since
the function iommu_present(dev->bus) return back 'arm_smmu_ops' so you
could see the code will run into below logic:
vfio_iommu_group_get()
{
group = iommu_group_get(dev);
#ifdef CONFIG_VFIO_NOIOMMU
/*
* With noiommu enabled, an IOMMU group will be created for a device
* that doesn't already have one and doesn't have an iommu_ops on their
* bus. We set iommudata simply to be able to identify these groups
* as special use and for reclamation later.
*/
if (group || !noiommu || iommu_present(dev->bus))
return group; ==> return 'group' and 'group' is NULL
[...]
}
So either using SMMU or with kernel config CONFIG_VFIO_NOIOMMU, both cannot
bind vifo driver for network card device on Juno-r2 board.
P.s. I also checked the sysfs node and found it doesn't contain node
'iommu_group':
# ls /sys/bus/pci/devices/0000\:08\:00.0/iommu_group
ls: cannot access '/sys/bus/pci/devices/0000:08:00.0/iommu_group': No
such file or directory
Could you give some suggestions for this so that I can proceed? Very
appreciate for any comment.
Thanks,
Leo Yan
[1] http://infocenter.arm.com/help/topic/com.arm.doc.ddi0515f/DDI0515F_juno_arm_development_platform_soc_trm.pdf
[2] https://www.linaro.org/blog/kvm-pciemsi-passthrough-armarm64/
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