linux-kernel - Re: [PATCH] mm/x86: Patch out arch_flush_lazy_mmu

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Date:	Thu, 28 Feb 2013 16:15:45 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Josh Boyer <jwboyer@...hat.com>
CC:	Borislav Petkov <bp@...en8.de>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>, mingo@...hat.com,
	tglx@...utronix.de, konrad.wilk@...cle.com, rostedt@...dmis.org,
	gregkh@...uxfoundation.org, samu.kallio@...rdeencloud.com,
	kraman@...hat.com, xen-devel@...ts.xen.org,
	linux-kernel@...r.kernel.org, stable@...nel.org
Subject: Re: [PATCH] mm/x86: Patch out arch_flush_lazy_mmu_mode() when running
 on bare metal

On 02/28/2013 04:05 PM, Josh Boyer wrote:
> On Fri, Mar 01, 2013 at 12:37:20AM +0100, Borislav Petkov wrote:
>> On Thu, Feb 28, 2013 at 05:55:49PM -0500, Boris Ostrovsky wrote:
>>> Invoking arch_flush_lazy_mmu_mode() results in calls to
>>> preempt_enable()/disable() which may have performance impact.
>>>
>>> Since lazy MMU is not used on bare metal we can patch away
>>> arch_flush_lazy_mmu_mode() so that it is never called in such
>>> environment.
>>>
>>> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>
>>
>> Looks straight-forward enough to me.
>>
>> Acked-by: Borislav Petkov <bp@...e.de>
> 
> I'll try to get someone to test this tomorrow.
> 

Sounds good.

I'd like look at this after the merge window close.  I'm kind of
bothered about having a choice with an oops on PV, a performance
regression on native, or putting a pretty complex patch in as a fix, but
since we'll be right after -rc1 it is probably reasonable to pick the
last option.

	-hpa

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