[Xen-users] PCI Passthrough for an HVM?

[Eric <epretorious@xxxxxxxxx>]

After much consternation, I've successfully established PCI passthrough for a 
paravirtualized (PV) guest 
(https://www.centos.org/forums/viewtopic.php?f=14&t=54409). However, I'm not 
able to pass the same device (A dual-port, Gigabit NIC) to hardware-assisted 
(HVM) guests (after destroying the PV guest with control over the NIC).


> 01:0a.0 Ethernet controller: Intel Corporation 82546EB Gigabit Ethernet 
> Controller (Copper) (rev 01)
>     Subsystem: Compaq Computer Corporation NC7170 Gigabit Server Adapter
>     Kernel driver in use: pciback
> 01:0a.1 Ethernet controller: Intel Corporation 82546EB Gigabit Ethernet 
> Controller (Copper) (rev 01)
>     Subsystem: Compaq Computer Corporation NC7170 Gigabit Server Adapter
>     Kernel driver in use: pciback


Looking into the host's kernel ring buffer, there are several messages related 
to the device. One, in particular, stands out (at the end of this block):

> pciback 0000:01:0a.0: seizing device
> pciback 0000:01:0a.1: seizing device
> ...
> xen_pciback: backend is vpci
> ...
> xen_pciback: vpci: 0000:01:0a.0: assign to virtual slot 0
> xen-blkback:ring-ref 8, event-channel 8, protocol 1 (x86_64-abi) persistent 
> grants

> ....

> pciback 0000:01:0a.0: Driver tried to write to a read-only configuration 
> space field at offset 0xf2, size 2. This may be \
>   harmless, but if you have problems with your device:
> 1) see permissive attribute in sysfs
> 2) report problems to the xen-devel mailing list along with details of your 
> device obtained from lspci.
> ...
> pciback 0000:01:0a.1: Driver tried to write to a read-only configuration 
> space field at offset 0xf2, size 2. This may be harmless, > but if you have 
> problems with your device:
> 1) see permissive attribute in sysfs
> 2) report problems to the xen-devel mailing list along with details of your 
> device obtained from lspci.


But, looking in the sysfs...

> [root@xen-home untangle]# tree /sys/devices/pci-24-0/
> /sys/devices/pci-24-0/
> âââ devtype
> âââ driver -> ../../bus/xen-backend/drivers/xen-pciback
> âââ modalias
> âââ nodename
> âââ power
> â   âââ autosuspend_delay_ms
> â   âââ control
> â   âââ runtime_active_time
> â   âââ runtime_status
> â   âââ runtime_suspended_time
> âââ subsystem -> ../../bus/xen-backend
> âââ uevent
> 
> [root@xen-home untangle]# tree /sys/bus/xen-backend/devices/
> /sys/bus/xen-backend/devices/
> âââ console-24-0 -> ../../../devices/console-24-0
> âââ pci-24-0 -> ../../../devices/pci-24-0
> âââ qdisk-24-5632 -> ../../../devices/qdisk-24-5632
> âââ vbd-24-768 -> ../../../devices/vbd-24-768
> âââ vif-24-0 -> ../../../devices/vif-24-0
> âââ vkbd-24-0 -> ../../../devices/vkbd-24-0

...I don't see anything that looks like it controls the permissive attribute of 
the device.

What have I overlooked?

Eric Pretorious
Portland, OR

* https://www.centos.org/forums/viewtopic.php?f=14&t=54409

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