From mboxrd@z Thu Jan  1 00:00:00 1970
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Subject: Re: [PATCH] kvm/ppc: interrupt disabling fixes
Date: Thu, 09 May 2013 12:51:54 +1000
Message-ID: <1368067914.25488.154.camel@pasglop>
References: <1368059739.3398.64@snotra>
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Cc: "tiejun.chen" <tiejun.chen@windriver.com>,
	Alexander Graf <agraf@suse.de>, kvm-ppc@vger.kernel.org,
	kvm@vger.kernel.org, Mihai Caraman <mihai.caraman@freescale.com>
To: Scott Wood <scottwood@freescale.com>
Return-path: <kvm-ppc-owner@vger.kernel.org>
In-Reply-To: <1368059739.3398.64@snotra>
Sender: kvm-ppc-owner@vger.kernel.org
List-Id: kvm.vger.kernel.org

On Wed, 2013-05-08 at 19:35 -0500, Scott Wood wrote:

> Sigh, and then there's this:
> 
> #ifdef CONFIG_PPC64
>                  /* lazy EE magic */
>                  hard_irq_disable();
>                  if (lazy_irq_pending()) {
>                          /* Got an interrupt in between, try again */
>                          local_irq_enable();
>                          hard_irq_disable();
>                          kvm_guest_exit();
>                          continue;
>                  }
> 
>                  trace_hardirqs_on();
> #endif
> 
> Alex, could you be a bit more descriptive than "magic" please?  Can  
> this chunk of code be removed if we do the other changes being  
> discussed?  Or should we leave this in and drop the pre-enter  
> hard_irq_disable portion of the proposed changes?
> 
> Why are you calling trace_hardirqs_on() here and not in  
> kvmppc_lazy_ee_enable()?  Why are you calling kvm_guest_exit() before  
> you've called kvm_guest_enter()?

I think I originated that magic... it more/less mimmics prep_for_idle,
the goal was to hard disable (because we had soft disabled earlier) and
check if anything happened in between... if it did, abort, and try
again, but it's a bit fishy really.

Ben.