linux-kernel - Re: [RESEND 2][PATCH 4/4] Modify KVM to update guest time accounting.

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Date:	Mon, 15 Oct 2007 13:38:56 +0200
From:	Laurent Vivier <Laurent.Vivier@...l.net>
To:	Christian Borntraeger <borntraeger@...ibm.com>
Cc:	Avi Kivity <avi@...ranet.com>, Ingo Molnar <mingo@...e.hu>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [RESEND 2][PATCH 4/4] Modify KVM to update guest time accounting.

Christian Borntraeger wrote:
> Am Montag, 15. Oktober 2007 schrieb Avi Kivity:
>> We can clear it a bit later, after local_irq_enable() in __vcpu_run().  
>> However we need a nop instruction first because "sti" keeps interrupts 
>> disabled for one more instruction.
> 
> Ah, I see. The host interrupt  behaves different and instead of running the
> interrupt handler, it exits the vmrun on x86? The interrupt handler will be
> called some cycles after the sti?
> That is different to s390. We can run the guest code for a long time and the
> host instruction pointer stays on the sie instruction. That means, we can 
> interrupt sie and continue by simply setting the instrution pointer (PSW) 
> back to the sie instruction.
> 
> Any idea how to make this proper on all architectures? I will have a look.

I think the solution is to have an arch dependent kvm_guest_exit(): empty for
x86, clearing the bit for s390.

Regards,
Laurent
-- 
---------------- Laurent.Vivier@...l.net  -----------------
"Given enough eyeballs, all bugs are shallow" E. S. Raymond


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