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

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Message-ID: <56C5DA62.8080204@redhat.com>
Date:	Thu, 18 Feb 2016 15:51:14 +0100
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Radim Krčmář <rkrcmar@...hat.com>,
	Suravee Suthikulpanit <Suravee.Suthikulpanit@....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
Subject: Re: [PART1 RFC 5/9] svm: Add VMEXIT handlers for AVIC



On 18/02/2016 15:18, Radim Krčmář wrote:
> KVM just has to make sure that targeted VCPUs notice the interrupt,
> which means to kick (wake up) VCPUs that don't have IsRunning set.
> There is no need to do anything with running VCPUs, because they
>  - are in guest mode and noticed the doorbell
>  - are in host mode, where they will
>    1) VMRUN as fast as they can because the VCPU didn't want to halt
>       (and IRR is handled on VMRUN)
>    2) check IRR after unsetting IsRunning and goto (1) if there are
>       pending interrupts.  (RFC doesn't do this, which is another bug)

This is not necessary.  IsRunning is only cleared at vcpu_put time.  The
next KVM_RUN will look at IRR (kvm_arch_vcpu_runnable), if necessary set
the mp_state to KVM_MP_STATE_RUNNABLE, and do the VMRUN.

But I agree that this is what Suravee is missing.

> It's still possible that we misunderstood the spec.  Does AVIC handle
> IPIs differently?

I don't think we misunderstood it.  Well, I did, but that's fixed now. :)

Paolo