linux-kernel - Re: [PATCH v2 3/8] x86: Store a per-cpu shadow copy of CR4

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Date:	Sat, 1 Nov 2014 20:56:20 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Andy Lutomirski <luto@...capital.net>
cc:	Peter Zijlstra <peterz@...radead.org>,
	Valdis Kletnieks <Valdis.Kletnieks@...edu>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Kees Cook <keescook@...omium.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Vince Weaver <vince@...ter.net>,
	"hillf.zj" <hillf.zj@...baba-inc.com>, x86@...nel.org
Subject: Re: [PATCH v2 3/8] x86: Store a per-cpu shadow copy of CR4

On Fri, 24 Oct 2014, Andy Lutomirski wrote:

> Context switches and TLB flushes can change individual bits of CR4.
> CR4 reads take several cycles, so store a shadow copy of CR4 in a
> per-cpu variable.
> 
> To avoid wasting a cache line, I added the CR4 shadow to
> cpu_tlbstate, which is already touched in switch_mm.  The heaviest
> users of the cr4 shadow will be switch_mm and __switch_to_xtra, and
> __switch_to_xtra is called shortly after switch_mm during context
> switch, so the cacheline is likely to be hot.
> 
> Signed-off-by: Andy Lutomirski <luto@...capital.net>

Reviewed-by: Thomas Gleixner <tglx@...utronix.de>
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