linux-kernel - Re: [PATCH 2/3] x86,mm: drop TLB flush from ptep_set_access

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Date:	Sat, 17 Nov 2012 15:50:15 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Rik van Riel <riel@...hat.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Ingo Molnar <mingo@...nel.org>,
	Andi Kleen <andi@...stfloor.org>,
	Michel Lespinasse <walken@...gle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Mel Gorman <mgorman@...e.de>,
	Johannes Weiner <hannes@...xchg.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	florian@...nwrt.org, Borislav Petkov <borislav.petkov@....com>
Subject: Re: [PATCH 2/3] x86,mm: drop TLB flush from ptep_set_access_flags

On Mon, Oct 29, 2012 at 10:06:15AM -0700, Linus Torvalds wrote:
> On Mon, Oct 29, 2012 at 9:57 AM, Borislav Petkov <bp@...en8.de> wrote:
> >
> > On current AMD64 processors,
> 
> Can you verify that this is true for older cpu's too (ie the old
> pre-64-bit ones, say K6 and original Athlon)?

Albeit with a slight delay, the answer is yes: all AMD cpus
automatically invalidate cached TLB entries (and intermediate walk
results, for that matter) on a #PF.

I don't know, however, whether it would be prudent to have some sort of
a cheap assertion in the code (cheaper than INVLPG %ADDR, although on
older cpus we do MOV CR3) just in case. This should be enabled only with
DEBUG_VM on, of course...

HTH.

-- 
Regards/Gruss,
Boris.
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