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

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Message-ID: <CALCETrX5JEZ3cLbuehobnH3bmBDAKARV9o0V5VYoazV8rL5o-A@mail.gmail.com>
Date:	Wed, 10 Sep 2014 13:31:27 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Toshi Kani <toshi.kani@...com>,
	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, Sep 10, 2014 at 1:14 PM, H. Peter Anvin <hpa@...or.com> wrote:
> On 09/10/2014 12:30 PM, Toshi Kani wrote:
>>
>> When WT is unavailable due to the PAT errata, it does not fail but gets
>> redirected to UC-.  Similarly, when PAT is disabled, WT gets redirected
>> to UC- as well.
>>
>
> But on pre-PAT hardware you can still do WT.
>

Using MTRRs?  /me shudders, although I suppose this would be okay for
NV-DIMMs as long as you map the whole thing WT.

One of these days I'll finish excising mtrr_add from everything
outside arch/x86.  I already killed it in all modern graphics drivers
:)

--Andy



>         -hpa
>



-- 
Andy Lutomirski
AMA Capital Management, LLC
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