linux-kernel - Re: runtime regression with "x86/mm/pat: Emulate PAT when it is disabled"

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Date:	Fri, 11 Mar 2016 23:16:51 +0100
From:	Borislav Petkov <bp@...e.de>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Toshi Kani <toshi.kani@....com>,
	Richard Purdie <richard.purdie@...uxfoundation.org>,
	Toshi Kani <toshi.kani@...com>,
	Bruce Ashfield <bruce.ashfield@...driver.com>,
	"Hart, Darren" <darren.hart@...el.com>,
	"saul.wold" <saul.wold@...el.com>, linux-kernel@...r.kernel.org,
	kvm ML <kvm@...r.kernel.org>, x86-ml <x86@...nel.org>
Subject: Re: runtime regression with "x86/mm/pat: Emulate PAT when it is
 disabled"

On Fri, Mar 11, 2016 at 08:18:23PM +0100, Paolo Bonzini wrote:
> Somebody got it wrong 10-ish years ago, and nobody has ever checked since.
> 
> But, don't use qemu32 or qemu64.  Use kvm32 and kvm64, or better
> something like the host you run on ("-cpu Nehalem", "-cpu SandyBridge",
> "-cpu Haswell-noTSX" etc.).

Paul, Richard, how about it?

> I really, really should fix those defaults...

Here's a start, while I have everything fresh in my head.

---
From: Borislav Petkov <bp@...e.de>
Date: Fri, 11 Mar 2016 23:11:05 +0100
Subject: [PATCH] target-i386/cpu: Correct MTRR and PAT feature bits

Pentium Pro had MTRRs but not PAT, PAT support appeared in Pentium III.
Fix all defines.

Signed-off-by: Borislav Petkov <bp@...e.de>
---
 target-i386/cpu.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/target-i386/cpu.c b/target-i386/cpu.c
index 0f38d1eae317..fa7ea4a8c229 100644
--- a/target-i386/cpu.c
+++ b/target-i386/cpu.c
@@ -308,12 +308,12 @@ static const char *cpuid_6_feature_name[] = {
 #define PENTIUM_FEATURES (I486_FEATURES | CPUID_DE | CPUID_TSC | \
           CPUID_MSR | CPUID_MCE | CPUID_CX8 | CPUID_MMX | CPUID_APIC)
 #define PENTIUM2_FEATURES (PENTIUM_FEATURES | CPUID_PAE | CPUID_SEP | \
-          CPUID_MTRR | CPUID_PGE | CPUID_MCA | CPUID_CMOV | CPUID_PAT | \
+          CPUID_MTRR | CPUID_PGE | CPUID_MCA | CPUID_CMOV | \
           CPUID_PSE36 | CPUID_FXSR)
-#define PENTIUM3_FEATURES (PENTIUM2_FEATURES | CPUID_SSE)
+#define PENTIUM3_FEATURES (PENTIUM2_FEATURES | CPUID_SSE | CPUID_PAT)
 #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 | \
+          CPUID_MTRR | CPUID_FXSR | CPUID_MMX | CPUID_SSE | CPUID_SSE2 | \
           CPUID_PAE | CPUID_SEP | CPUID_APIC)
 
 #define TCG_FEATURES (CPUID_FP87 | CPUID_PSE | CPUID_TSC | CPUID_MSR | \
-- 
2.3.5

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
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