From mboxrd@z Thu Jan  1 00:00:00 1970
From: "tiejun.chen" <tiejun.chen@windriver.com>
Subject: Re: [v1][PATCH 1/1] KVM: PPC: disable preemption when using hard_irq_disable()
Date: Thu, 11 Jul 2013 11:00:33 +0800
Message-ID: <51DE1FD1.90609@windriver.com>
References: <1373436139-27998-1-git-send-email-tiejun.chen@windriver.com> <1373483740.8183.223@snotra>
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Cc: <agraf@suse.de>, <kvm-ppc@vger.kernel.org>, <kvm@vger.kernel.org>,
	<linuxppc-dev@lists.ozlabs.org>
To: Scott Wood <scottwood@freescale.com>
Return-path: <kvm-ppc-owner@vger.kernel.org>
In-Reply-To: <1373483740.8183.223@snotra>
Sender: kvm-ppc-owner@vger.kernel.org
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On 07/11/2013 03:15 AM, Scott Wood wrote:
> On 07/10/2013 01:02:19 AM, Tiejun Chen wrote:
>> We should ensure the preemption cannot occur while calling get_paca()
>> insdide hard_irq_disable(), otherwise the paca_struct may be the
>> wrong one just after. And btw, we may update timing stats in this case.
>
> The soft-ee mechanism depends on accessing the PACA directly via r13 to avoid
> this.  We probably should be using inline asm to read was_enabled rather than

Yes.

> hoping the compiler doesn't do anything silly.

Do you recommend I should directly replace get_paca() with local_paca inside 
hard_irq_disable()?

#define hard_irq_disable()      do {                    \
         u8 _was_enabled = get_paca()->soft_enabled;     \

->	u8 _was_enabled = local_paca->soft_enabled;

But is this safe for all scenarios?

Tiejun