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

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Date:	Mon, 15 Oct 2007 13:15:26 +0200
From:	Avi Kivity <avi@...ranet.com>
To:	Laurent Vivier <Laurent.Vivier@...l.net>
CC:	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.

Laurent Vivier wrote:
> Avi Kivity wrote:
>   
>> Ingo Molnar wrote:
>>     
>>> * Avi Kivity <avi@...ranet.com> wrote:
>>>
>>>  
>>>       
>>>> This bit can go; for the external module I can add it back in
>>>> external-module-compat.h.  No need to pollute mainline with backward
>>>> compatibility stuff.
>>>>     
>>>>         
>>> hm:
>>>
>>> static inline void kvm_guest_enter(void)
>>> {
>>>         current->flags |= PF_VCPU;
>>> }
>>>
>>> static inline void kvm_guest_exit(void)
>>> {
>>> }
>>>
>>> shouldnt PF_VCPU be cleared in kvm_guest_exit()?
>>>   
>>>       
>> IIRC the accounting code clears it, but yes, it may not have been called
>> at all, so clearing it here is needed.
>>
>>     
>
> No, It must not be cleared here because we can't enter in the accounting code
> between kvm_guest_enter(void) and kvm_guest_exit(void).
>
>   

Right.

> This is why the accounting code clears it.
>   

But if we didn't get an interrupt in that time?

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.


-- 
error compiling committee.c: too many arguments to function

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