linux-kernel - Re: [PATCH] x86, pat: Add comments to cachemode translation tables

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Message-ID: <1438614488.3214.466.camel@hp.com>
Date:	Mon, 03 Aug 2015 09:08:08 -0600
From:	Toshi Kani <toshi.kani@...com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Jan Beulich <JBeulich@...e.com>, peterz@...radead.org,
	mingo@...nel.org, x86@...nel.org, bp@...e.de,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86, pat: Add comments to cachemode translation tables

On Sun, 2015-08-02 at 12:07 +0200, Thomas Gleixner wrote:
> On Thu, 23 Jul 2015, Toshi Kani wrote:
> > On Thu, 2015-07-23 at 09:36 -0600, Jan Beulich wrote:
> > > > 
> > > > > > On 23.07.15 at 17:25, <toshi.kani@...com> wrote:
> > > > Yes, I agree with you.  But such risk is very low -- 1) the regular 
> > > > case
> > > > (no fallback) is used most of the cases, 2) the code using WT knows 
> > > > what
> > > > type of memory it is dealing with.  For example, pmem may map NVDIMM 
> > > > 
> > > > with
> > > > WT, and any sane BIOS sets MTRR to WB for NVDIMM. 
> > > 
> > > Do the words "sane" and "BIOS" really fit together in your opinion?
> > 
> > :-)
> > 
> > Anyway, I am not disagreeing with you... When UC is ready for both 
> > regular
> > memory and IO memory, it should be changed to fall back to UC.
> 
> What's the resolution of this discussion? Is that patch correct as is
> or do we get an updated version?

Yes, this patch is correct and we are in agreement.

What Jan mentioned about falling back to UC, instead of UC-, is a separate
item, and the code does not support it yet.

Thanks,
-Toshi
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