Re: Optimized clocksource with AMD AVIC enabled for Windows guest

[Vitaly Kuznetsov <vkuznets@redhat.com>]

Paolo Bonzini <pbonzini@redhat.com> writes:

> On 03/02/21 07:40, Kechen Lu wrote:
>> From the above observations, trying to see if there's a way for
>> enabling AVIC while also having the most optimized clock source for
>> windows guest.
>> 
>
> You would have to change KVM, so that AVIC is only disabled if Auto-EOI 
> interrupts are used.
>

(I vaguely recall having this was discussed already but apparently no
changes were made since)

Hyper-V TLFS defines the following bit:

CPUID 0x40000004.EAX 
Bit 9: Recommend deprecating AutoEOI.

But this is merely a recommendation and older Windows versions may not
know about the bit and still use it. We need to make sure the bit is
set/exposed to Windows guests but we also must track AutoEOI usage and
inhibit AVIC when detected.

-- 
Vitaly