linux-kernel - Re: kvm: RCU warning in async pf

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Date:	Wed, 4 Apr 2012 22:13:13 +0200
From:	Sasha Levin <levinsasha928@...il.com>
To:	Gleb Natapov <gleb@...hat.com>
Cc:	Avi Kivity <avi@...hat.com>, Marcelo Tosatti <mtosatti@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	kvm <kvm@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Dave Jones <davej@...hat.com>
Subject: Re: kvm: RCU warning in async pf

On Wed, Apr 4, 2012 at 2:30 PM, Gleb Natapov <gleb@...hat.com> wrote:
> On Tue, Apr 03, 2012 at 01:52:26PM +0300, Gleb Natapov wrote:
>> On Mon, Apr 02, 2012 at 08:54:32PM -0400, Sasha Levin wrote:
>> > Hi all,
>> >
>> > I got the spew at the bottom of the mail in a KVM guest using the KVM tools and running trinity.
>> >
>> > I'm not quite sure how default_idle managed to trigger a pagefault, so that part looks odd to me.
>> >
>> This is not regular page fault. This is async page fault that tells the
>> guest that a page, previously swapped out by hypervisor, is now swapped
>> back in and it can happen while vcpu is idle. The code does not leave
>> idle state properly though. We probably need to call rcu_irq_enter()
>> there. Will look into it.
>>
>
> The patch below solves it for me:
>
> "Page ready" async PF can kick vcpu out of idle state much like IRQ.
> We need to tell RCU about this.

Looks good here.
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