Re: [PART1 RFC 5/9] svm: Add VMEXIT handlers for AVIC

[Paolo Bonzini]

On 18/02/2016 17:27, Radim KrÄmÃÅ wrote:
> 2016-02-18 16:53+0100, Paolo Bonzini:
>> Patch 9 is okay, but it is also necessary to clear IsRunning in
>> kvm_arch_vcpu_blocking and set it in kvm_arch_vcpu_unblocking.  In
>> addition, vcpu_put/vcpu_load should not modify IsRunning between
>> kvm_arch_vcpu_blocking and kvm_arch_vcpu_unblocking.  Do you agree?
> 
> Yes.
> 
> I think we don't need to clear IsRunning on preemption, which would
> simplify the protection.  (I haven't thought much about userspace exit,
> so maybe we could skip that one as well, but we don't need to now.)
> 
> The reason for that is that KVM knows that the VCPU was scheduled out,
> so it couldn't do much in the AVIC VMEXIT.
> (KVM could force scheduler to pritioritize the VCPU, but our kick
>  doesn't do that now and it seems like a bad idea.)
> 
> Does it seem reasonable?

Yes, and in fact it wouldn't need to clear and set IsRunning on
vcpu_put/vcpu_load; only on vcpu_blocking/vcpu_unblocking.

The IsRunning flag is more of a IsNotHalted flag, in the end.

Paolo