linux-kernel - Re: [tip:x86/mm] x86/mm/mtrr: Clean up mtrr_type

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Message-ID: <20150731150806.GX25159@twins.programming.kicks-ass.net>
Date:	Fri, 31 Jul 2015 17:08:06 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Borislav Petkov <bp@...en8.de>
Cc:	mingo@...nel.org, hpa@...or.com, dvlasenk@...hat.com, bp@...e.de,
	akpm@...ux-foundation.org, brgerst@...il.com, tglx@...utronix.de,
	linux-mm@...ck.org, luto@...capital.net, mcgrof@...e.com,
	toshi.kani@...com, torvalds@...ux-foundation.org,
	linux-kernel@...r.kernel.org, linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/mm] x86/mm/mtrr: Clean up mtrr_type_lookup()

On Fri, Jul 31, 2015 at 04:44:52PM +0200, Borislav Petkov wrote:
> On Fri, Jul 31, 2015 at 03:18:02PM +0200, Peter Zijlstra wrote:
> > Using these functions with preemption enabled is racy against MTRR
> > updates. And if that race is ok, at the very least explain that it is
> > indeed racy and why this is not a problem.
> 
> Right, so Luis has been working on burying direct MTRR access so
> after that work is done, we'll be using only PAT for changing memory
> attributes. Look at arch_phys_wc_add() and all those fbdev users of
> mtrr_add() which get converted to that thing...

Drivers don't do those lookups afaict.

But its things like set_memory_XX(), and afaict that's all buggy against
MTRR modifications.
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