Re: [PATCH v2 06/19] iommufd/viommu: Add IOMMU_VIOMMU_SET/UNSET_VDEV_ID ioctl

Alexey Kardashevskiy
2025-05-06T04:35:23Z

On 6/5/25 12:53, Nicolin Chen wrote:
> On Mon, May 05, 2025 at 02:08:07PM -0300, Jason Gunthorpe wrote:
>> On Wed, Apr 30, 2025 at 12:58:47AM -0700, Nicolin Chen wrote:
>>
>>>> ... and I just hit a problem with it - this is basically guest BDFn
>>>> and it works as long as I'm hotplugging the TEE-IO VF into an SNP VM
>>>> but does not when I pass through via the QEMU cmdline - bus numbers
>>>> are not assigned yet. So I have to postpone the vdevice allocation
>>>> till run time, did I miss something here? Thanks,
>>>
>>> I have a similar case with QEMU ARM64's VM: so vDEVICE on ARM is
>>> allocated at runtime as well because the BDF number isn't ready
>>> at the boot time.
>>
>> Oh that's ugly then.. So you'll need to add some kind of 'modify
>> sid/bdf' operation I think.
>
> But the initial vDEVICE would be still unusable. Its BDF number is
> literally 0 in my case. It can't be used for SID-based invalidation
> nor the reverse vSID lookup for fault injection..
>
>> The bus numbers can be reassigned at any time on the fly by the guest
>> by reprogramming the PCI hierarchy.
>
> Yes. If we take some aggressive use case into account, where its
> BDF number could change multiple times, I think it's natural for
> VMM to simply destroy the previous vDEVICE and allocate a new one
> with a new BDF number, right?

Yup, this sounds about right, recreate on the bus number change.

>
> Thanks
> Nicolin

--
Alexey