Re: [PATCH] x86:kvm:hyperv: make VP_INDEX managed by userspace

["Radim Krčmář" <rkrcmar@redhat.com>]

2017-06-16 18:16+0300, Roman Kagan:
> Hyper-V identifies vCPUs by Virtual Processor Index, which can be
> queried via HV_X64_MSR_VP_INDEX msr.  It is defined by the spec as a
> sequential number which can't exceed the maximum number of vCPUs per VM.
> APIC ids can be sparse and thus aren't a valid replacement for VP
> indices.
> 
> Current KVM uses its internal vcpu index as VP_INDEX.  However, to make
> it predictable and persistent across VM migrations, the userspace has to
> control the value of VP_INDEX.
> 
> This patch achieves that, by storing vp_index explicitly on vcpu, and
> allowing HV_X64_MSR_VP_INDEX to be set from the host side.  For
> compatibility it's initialized to KVM vcpu index.  Also a few variables
> are renamed to make clear distinction betweed this Hyper-V vp_index and
> KVM vcpu_id (== APIC id).
> 
> Signed-off-by: Roman Kagan <rkagan@virtuozzo.com>
> ---

Please add a kvm capability, so userspace doesn't trigger the unhandled
wrmsr messages when detecting this feature.

Thanks.