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

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Date:	Wed, 24 Feb 2010 11:28:44 +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

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? Never saw any
> warnings during my tests last year (granted: with older -rt and kvm
> versions).

Mmh, they could if there is > 1 IRQ pending. Guess this just never
triggered in real life due to typical APIC use and low IRQ load during
PIC times in my tests.

Jan

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