linux-kernel - Re: unnecessary tlb flush in mprotect

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20120522163735.GB1906@tassilo.jf.intel.com>
Date:	Tue, 22 May 2012 09:37:35 -0700
From:	Andi Kleen <ak@...ux.intel.com>
To:	Alex Shi <alex.shi@...el.com>
Cc:	"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
Subject: Re: unnecessary tlb flush in mprotect

On Tue, May 22, 2012 at 09:08:47AM +0800, Alex Shi wrote:
> 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?

I would be careful with TLB optimizations if it's not a clear performance
wins. A lot of these interactions are tricky and it's very easy to break
things in subtle and hard to debug ways.

-Andi
-- 
ak@...ux.intel.com -- Speaking for myself only
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/