Re: [RFC PATCH v1 00/38] ARM CCA Device Assignment support

Aneesh Kumar K.V
2025-08-05T04:50:37Z

<dan.j.williams@intel.com> writes:

> Aneesh Kumar K.V (Arm) wrote:
>> This patch series implements support for Device Assignment in the ARM CCA
>> architecture. The code changes are based on Alp12 specification published here
>> [1].
>>
>> The code builds on the TSM framework patches posted at [2]. We add extension to
>> that framework so that TSM is now used in both the host and the guest.
>>
>> A DA workflow can be summarized as below:
>>
>> Host:
>> step 1.
>> echo ${DEVICE} > /sys/bus/pci/devices/${DEVICE}/driver/unbind
>> echo vfio-pci > /sys/bus/pci/devices/${DEVICE}/driver_override
>> echo ${DEVICE} > /sys/bus/pci/drivers_probe
>>
>> step 2.
>> echo 1 > /sys/bus/pci/devices/$DEVICE/tsm/connect
>
> Just for my own understanding... presumably there is no ordering
> constraint for ARM CCA between step1 and step2, right? I.e. The connect
> state is independent of the bind state.
>
> In the v4 PCI/TSM scheme the connect command is now:
>
> echo $tsm_dev > /sys/bus/pci/devices/$DEVICE/tsm/connect
>
>> Now in the guest we follow the below steps
>
> I assume a signifcant amount of kvmtool magic happens here to get the
> TDI into a "bind capable" state, can you share that command?
>

lkvm run --realm -c 2 -m 256 -k /kselftest/Image -p "$KERNEL_PARAMS" -d ./rootfs-guest.ext2 --iommufd-vdevice --vfio-pci $DEVICE1 --vfio-pci $DEVICE2

> I had been assuming that everyone was prototyping with QEMU. Not a
> problem per se, but the memory management for shared device assignment /
> bounce buffering has had a quite of bit of work on the QEMU side, so
> just curious about the difference in approach here. Like, does kvmtool
> support operating the device in shared mode with bounce buffering and
> page conversion (shared <=> private) support? In any event, happy to see
> mutiple simultaneous consumers of this new kernel infrastructure.
>

-aneesh