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

[Suravee Suthikulpanit]

Hi

On 02/19/2016 12:18 AM, Paolo Bonzini wrote:
> 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

In facts, instead of setting up the vAPIC backing page address when 
calling kvm_arch_vcpu_load(), we should be able to do it when calling 
kvm_arch_vcpu_sched_in(). This seems more appropriate since the 
kvm_arch_vcpu_load() is also called in many unnecessary occasions via 
vcpu_load() (in the arch/x86/kvm/x86.c). The same goes for the 
kvm_arch_vcpu_put().

However, there is no kvm_arch_vcpu_sched_out(). But that can be added 
easily.

What do you think?

Suravee