linux-kernel - Re: [PATCH] KVM: x86: Kick VCPU outside PIC lock again

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Message-ID: <4B84FFEE.9020706@siemens.com>
Date:	Wed, 24 Feb 2010 11:31:10 +0100
From:	Jan Kiszka <jan.kiszka@...mens.com>
To:	Avi Kivity <avi@...hat.com>
CC:	Thomas Gleixner <tglx@...utronix.de>, KVM <kvm@...r.kernel.org>,
	Gleb Natapov <gleb@...hat.com>,
	RT <linux-rt-users@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] KVM: x86: Kick VCPU outside PIC lock again

Avi Kivity wrote:
> On 02/24/2010 12:22 PM, Jan Kiszka wrote:
>> Avi Kivity wrote:
>>    
>>> On 02/24/2010 12:13 PM, Jan Kiszka wrote:
>>>      
>>>>        
>>>>> I see.  Won't we hit the same issue when we call pic functions from
>>>>> atomic context during the guest entry sequence?
>>>>>
>>>>>
>>>>>          
>>>> If there are such call paths, for sure. What concrete path(s) do you
>>>> have in mind?
>>>>
>>>>
>>>>        
>>> vcpu_enter_guest() ->  inject_pending_event() ->
>>> kvm_cpu_{has,get}_interrupt() ->  various pic functions if you're unlucky.
>>>      
>> But do they kick anyone or just check/pull information?
> 
> Probably not, kicking should be a side effect (or rather the main 
> effect) of queueing an interrupt, not dequeuing it.
> 
>> Never saw any
>> warnings during my tests last year (granted: with older -rt and kvm
>> versions).
>>    
> 
> Well, most guests kill the pic early on.  Will apply the patch.
> 

I think it needs some extension: pic_irq_request should only schedule a
wake up on a rising edge of the PIC output.

Jan

-- 
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux
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