Re: [PATCH v2 1/2] viridian: remove implicit limit of 64 VPs per partition

[Anthony PERARD <anthony.perard@xxxxxxxxxx>]

On Tue, Jan 12, 2021 at 04:17:27AM +0000, Igor Druzhinin wrote:
> TLFS 7.8.1 stipulates that "a virtual processor index must be less than
> the maximum number of virtual processors per partition" that "can be obtained
> through CPUID leaf 0x40000005". Furthermore, "Requirements for Implementing
> the Microsoft Hypervisor Interface" defines that starting from Windows Server
> 2012, which allowed more than 64 CPUs to be brought up, this leaf can now
> contain a value -1 basically assuming the hypervisor has no restriction while
> 0 (that we currently expose) means the default restriction is still present.
> 
> Along with the previous changes exposing ExProcessorMasks this allows a recent
> Windows VM with Viridian extension enabled to have more than 64 vCPUs without
> going into BSOD in some cases.
> 
> Since we didn't expose the leaf before and to keep CPUID data consistent for
> incoming streams from previous Xen versions - let's keep it behind an option.
> 
> Signed-off-by: Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>

Acked-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>

Thanks,

-- 
Anthony PERARD