linux-kernel - Re: unnecessary tlb flush in mprotect

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Message-ID: <4FBAE71F.5000801@intel.com>
Date:	Tue, 22 May 2012 09:08:47 +0800
From:	Alex Shi <alex.shi@...el.com>
To:	"H. Peter Anvin" <hpa@...or.com>, cl@...ux-foundation.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>, mgorman@...e.de,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-mm@...r.kernel.org, Andi Kleen <ak@...ux.intel.com>
Subject: Re: unnecessary tlb flush in mprotect

On 05/21/2012 04:30 PM, Alex Shi wrote:

> when mprotect just change prots of non-present pages, current mprotect
> still do the tlb flush in check_protection().
> but according to 4.10.2.3 Intel SDM V3A (
> www.intel.com/Assets/ja_JP/PDF/manual/253668.pdf ) at that time, TLB has
> no this lines for this page. So, tlb flush is just waste time. (for cr3
> rewrite, flush all tlb, or invlpg, like a 'nop' in intel cpu)
> 
> Do we need to add the pte_present similar check here to prevent the
> unnecessary tlb flushing? I mean, are there real case in word, User like
> to change page prots before assign a physical page to it?
> 


Any comments from linux-mm emailing list?

> 
> 
> Alex Shi


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