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

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Date:	Thu, 3 Mar 2016 17:42:22 +0700
From:	Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>
To:	Paolo Bonzini <pbonzini@...hat.com>,
	Radim Krčmář <rkrcmar@...hat.com>
CC:	<joro@...tes.org>, <alex.williamson@...hat.com>, <gleb@...nel.org>,
	<kvm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<wei@...hat.com>, <sherry.hurwitz@....com>,
	"Wu, Feng" <feng.wu@...el.com>
Subject: Re: [PART1 RFC 5/9] svm: Add VMEXIT handlers for AVIC

Hi

On 02/19/2016 12:18 AM, Paolo Bonzini wrote:
>
>
> On 18/02/2016 17:27, Radim Krčmář 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