Re: [PATCH 4/9] Implement GIF, clgi and stgi v3

[Avi Kivity <avi@redhat.com>]

Alexander Graf wrote:
>>
>> Hmm yes, this is a problem. So this optimization will not work. We need
>> other ways to optimize :)
>
> Well it would work for the KVM-in-KVM case, where we know that VMRUN 
> is always triggered with IF=1 and V_INTR=1. The only case that hack 
> fails is when we have IF=0 and V_INTR=1. Everything else should work 
> just fine. And in this case we would simply issue some VMEXITs 0x60, 
> so no big deal IMHO. It should be worth the tradeoff of making most 
> VMMs a lot faster.
>
> There should be a compile-option to enable the "correct" behavior 
> though. If we join that with the VMLOAD and VMSAVE hack there would be 
> only the VMRUN and DR exits left. That sounds like a really good 
> improvement where I wouldn't mind to break some specs :-).

Maybe a hypercall, so it can be enabled on a guest-by-guest basis.

I must say that if we do guest-specific hacking this way, a paravirt 
approach doesn't look so bad.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.