Re: [edk2-devel] [PATCH] OvmfPkg: Set PcdCpuMaxLogicalProcessorNumber in OvmfXen

["Alejandro Vallejo via groups.io" <alejandro.vallejo=cloud.com@groups.io>]

On Thu Apr 25, 2024 at 2:58 PM BST, Gerd Hoffmann wrote:
>   Hi,
>  
> > It's a bit more complicated than setting it at build time, but we can
> > always ask Xen how many vcpu we have and set the PCD accordingly. This
> > is something that can happen in OvmfPkg/XenPlatformPei module.
>
> Exactly.
>
> > But to be honest, I don't know if it's worth it, because I don't know the
> > downside of having a higher value for PcdCpuMaxLogicalProcessorNumber.
>
> Well, the downside is that you have to keep ovmf and xen in sync
> manually.  Your call.  If you prefer to do it that way I have no
> objections, just wanted point out the alternative approach.
>
> take care,
>   Gerd

FYI, I've created a Xen Gitlab ticket to expose the maximum number of vCPUs as
discussed. It shoudn't be hard to expose the information in the Xen-specific
CPUID leaves at 0x4000000X (they are visible even with Viridian enabled, so that
should be fine).

I'll re-send a runtime version of this patch based on that information after
the required CPUID extension is in place.

https://gitlab.com/xen-project/xen/-/issues/191

Cheers,
Alejandro


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