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Date: Fri, 11 Mar 2016 13:23:56 +0000
From: One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk>
To: Borislav Petkov <bp@suse.de>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>,
        Toshi Kani <toshi.kani@hpe.com>,
        Richard Purdie <richard.purdie@linuxfoundation.org>,
        Toshi Kani <toshi.kani@hp.com>,
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        "Hart, Darren" <darren.hart@intel.com>,
        "saul.wold" <saul.wold@intel.com>, linux-kernel@vger.kernel.org
Subject: Re: runtime regression with "x86/mm/pat: Emulate PAT when it is
 disabled"
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On Thu, 10 Mar 2016 20:19:33 +0100
Borislav Petkov <bp@suse.de> wrote:

> On Thu, Mar 10, 2016 at 02:04:29PM -0500, Paul Gortmaker wrote:
> > So, I guess that is a qemu bug?  If there is no real silicon out there
> > that has no MTRR but does claim PAT, then qemu32 is a flawed CPU type?  
> 
> Well, AFAICT, "qemu32" is emulating something PPRO-like:
> 
> #define PPRO_FEATURES (CPUID_FP87 | CPUID_DE | CPUID_PSE | CPUID_TSC | \
>           CPUID_MSR | CPUID_MCE | CPUID_CX8 | CPUID_PGE | CPUID_CMOV | \
>           CPUID_PAT | CPUID_FXSR | CPUID_MMX | CPUID_SSE | CPUID_SSE2 | \
> 	  ^^^^^^^^^
> 
> and that one advertizes PAT but not MTRRs.
> 
> I need to go dig into history to find out what PPRO actually supported.

Pentium Pro has MTRR, PAT came later.

I believe the qemu32 CPU isn't a "real" CPU type therefore.

Alan