Re: [PATCH 04/17] gpu: nova-core: allocate PCI MSI vector during probe

[John Hubbard <jhubbard@nvidia.com>]

On 8/13/26 3:26 PM, Danilo Krummrich wrote:
> On Thu Aug 13, 2026 at 11:43 PM CEST, John Hubbard wrote:
>> On 8/13/26 2:31 PM, Danilo Krummrich wrote:
>>> On Sat Aug 8, 2026 at 5:11 AM CEST, John Hubbard wrote:
...
>>> I was about to ask if we really need to bother with MSI and shouln't just go for
>>> MSI-X only.
>>
>> I have an expensive, recent motherboard in my test machine, and it seems to only
>> expose MSI for my Turing, Ampere and Blackwell GPUs, in the non-SRIOV configuration.
>> So I'm thinking that MSI-X only would not work.
> 
> Interesting, I just checked one of my Ada and one of my Ampere GPUs and neither
> reports MSI-X in the capabilities. Other devices show up with MSI-X though...
> 
> Are we sure it's not an endpoint limitation? I really thought it's not.

I haven't really dug into it, because it seems very clear that regardless
of the answer, we need to support both MSI and MSI-X in nova-core, right?

> 
>>> But then saw that the commit message mentions broken VFIO setups; can you expand
>>> on this a bit? Which setups is the commit message referring to?
>>
>> On Zhi Wang's Big Branch of Everything, he is able to run Windows guests in a
>> vGPU VM on top of nova-core. That system requires MSI-X. And I broke it with
>> an earlier internal version of this patchset.
>>
>> That information probably leaked into my commit message here. I can remove
>> it. Because I don't think it is based on anything else.
> 
> So I guess we can also drop the INTx fallback? AFAIK SR-IOV VFs won't work with
> INTx anyway.
> 
We could drop it. It's there mainly on General Principles, not because today's
GPUs use it.

thanks,
-- 
John Hubbard