linux-kernel - Re: [PATCH v6 06/12] Add PV MSR to enable asynchronous page faults delivery.

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Date:	Sun, 10 Oct 2010 15:27:02 +0200
From:	Gleb Natapov <gleb@...hat.com>
To:	Avi Kivity <avi@...hat.com>
Cc:	kvm@...r.kernel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, mingo@...e.hu,
	a.p.zijlstra@...llo.nl, tglx@...utronix.de, hpa@...or.com,
	riel@...hat.com, cl@...ux-foundation.org, mtosatti@...hat.com
Subject: Re: [PATCH v6 06/12] Add PV MSR to enable asynchronous page faults
 delivery.

On Sun, Oct 10, 2010 at 02:47:43PM +0200, Avi Kivity wrote:
>  On 10/07/2010 07:53 PM, Gleb Natapov wrote:
> >On Thu, Oct 07, 2010 at 02:42:06PM +0200, Avi Kivity wrote:
> >>   On 10/04/2010 05:56 PM, Gleb Natapov wrote:
> >>  >Guest enables async PF vcpu functionality using this MSR.
> >>  >
> >>  >   			return NON_PRESENT;
> >>  >+
> >>  >+MSR_KVM_ASYNC_PF_EN: 0x4b564d02
> >>  >+	data: Bits 63-6 hold 64-byte aligned physical address of a 32bit memory
> >>
> >>  Given that it must be aligned anyway, we can require it to be a
> >>  64-byte region and also require that the guest zero it before
> >>  writing the MSR.  That will give us a little more flexibility in the
> >>  future.
> >>
> >No code change needed, so OK.
> 
> The guest needs to allocate a 64-byte per-cpu entry instead of a
> 4-byte entry.
> 
Yes, noticed that already :(

> 
> >>  >+
> >>  >+	kvm_async_pf_wakeup_all(vcpu);
> >>
> >>  Why is this needed?  If all apfs are flushed at disable time, what
> >>  do we need to wake up?
> >For migration. Destination will rewrite msr and all processes will be
> >waked up.
> 
> Ok. What happens to apf completions that happen after all vcpus are stopped?
> 
They will be cleaned by kvm_clear_async_pf_completion_queue() on vcpu
destroy.

--
			Gleb.
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