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

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Message-ID: <20120416125848.GT11918@redhat.com>
Date:	Mon, 16 Apr 2012 15:58:48 +0300
From:	Gleb Natapov <gleb@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Sasha Levin <levinsasha928@...il.com>, Avi Kivity <avi@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	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 Mon, Apr 16, 2012 at 01:28:55PM +0300, Gleb Natapov wrote:
> On Sat, Apr 14, 2012 at 11:44:53AM +0200, Peter Zijlstra wrote:
> > On Wed, 2012-04-04 at 15:30 +0300, Gleb Natapov wrote:
> > >  
> > > @@ -253,7 +254,10 @@ do_async_page_fault(struct pt_regs *regs, unsigned long error_code)
> > >  		kvm_async_pf_task_wait((u32)read_cr2());
> > >  		break;
> > >  	case KVM_PV_REASON_PAGE_READY:
> > > +		rcu_irq_enter();
> > > +		exit_idle();
> > >  		kvm_async_pf_task_wake((u32)read_cr2());
> > > +		rcu_irq_exit();
> > >  		break;
> > >  	}
> > >  }
> > 
> > Wouldn't irq_enter() / irq_exit() be more appropriate? You're basically
> > taking an interrupt/exception from idle, irq_enter() will fix up
> > everything that needs fixing up, including time sources (which the
> > scheduler expects to be up-to-date).
> > 
> You are right. Will send a patch.
> 

KVM: Call irq_enter() instead of rcu_irq_enter() during async PF.

As Peter noted there are more things that should be done when leaving
idle state. irq_(enter|exit)() does them and also call rcu functions.

Signed-off-by: Gleb Natapov <gleb@...hat.com>
diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index b8ba6e4..83a48f6 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -254,10 +254,10 @@ do_async_page_fault(struct pt_regs *regs, unsigned long error_code)
 		kvm_async_pf_task_wait((u32)read_cr2());
 		break;
 	case KVM_PV_REASON_PAGE_READY:
-		rcu_irq_enter();
+		irq_enter();
 		exit_idle();
 		kvm_async_pf_task_wake((u32)read_cr2());
-		rcu_irq_exit();
+		irq_exit();
 		break;
 	}
 }
--
			Gleb.
--
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