linux-kernel - Re: [PATCH v2 2/6] x86, mm, pat: Change reserve

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Date:	Wed, 10 Sep 2014 15:47:53 -0600
From:	Toshi Kani <toshi.kani@...com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Andy Lutomirski <luto@...capital.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arnd Bergmann <arnd@...db.de>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Juergen Gross <jgross@...e.com>,
	Stefan Bader <stefan.bader@...onical.com>,
	Henrique de Moraes Holschuh <hmh@....eng.br>,
	Yigal Korman <yigal@...xistor.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Subject: Re: [PATCH v2 2/6] x86, mm, pat: Change reserve_memtype() to handle
 WT

On Wed, 2014-09-10 at 14:39 -0700, H. Peter Anvin wrote:
> On 09/10/2014 02:27 PM, Andy Lutomirski wrote:
> >>
> >> That's possible, but the only benefit is that we can enable WT on
> >> pre-PAT systems, which I do not think anyone cares now...  WB & UC work
> >> on pre-PAT systems.  WC & WT need PAT.  I think this requirement is
> >> reasonable.
> > 
> > It might end up being a cleanup, though.  A whole bunch of
> > rarely-exercised if (!pat_enabled) things would go away.
> > 
> 
> Yes.  Don't think of it as PAT vs non-PAT.  Think of it as a specific
> set of cache types available on different processors.  The fact that you
> may have to frob an MSR to initialize it is almost trivial in comparison.

Right.

Thanks,
-Toshi

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