linux-kernel - [PATCH RFC] x86: clear X86_FEATURE

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Date:	Fri, 6 Apr 2007 00:51:41 +0200
From:	Andreas Herrmann <aherrman@...or.de>
To:	Andi Kleen <ak@...e.de>, "H. Peter Anvin" <hpa@...or.com>
Cc:	linux-kernel@...r.kernel.org, andreas.herrmann3@....com
Subject: [PATCH RFC] x86: clear X86_FEATURE_MWAIT for AMD Fam10 CPU

Hi,

I send this as RFC because I won't manage it to test it
before end of Easter but want to have a consensus about
how the final patch should look like.

Andi,
what do you finally prefer?

(1) Something like the attached patch or
(2) a version which keeps to the MWAIT flag for Fam10 but
    introduces an X86_FEATURE_MWAIT_DOESNT_SAVE_POWER as you
    suggested.

An idle=mwait kernel parameter could (and should) be introduced
with both alternatives.

Meanwhile I think it would suffice to do (1) and issue another
cpuid if idle=mwait was used to select mwait_idle.

Regards,

Andreas

--

diff --git a/arch/i386/kernel/cpu/amd.c b/arch/i386/kernel/cpu/amd.c
index 2d47db4..4e01262 100644
--- a/arch/i386/kernel/cpu/amd.c
+++ b/arch/i386/kernel/cpu/amd.c
@@ -228,6 +228,9 @@ #define CBAR_KEY	(0X000000CB)
 	}

 	switch (c->x86) {
+	case 16:
+		clear_bit(X86_FEATURE_MWAIT, c->x86_capability);
+		break;
 	case 15:
 		set_bit(X86_FEATURE_K8, c->x86_capability);
 		break;
diff --git a/arch/x86_64/kernel/setup.c b/arch/x86_64/kernel/setup.c
index 3d98b69..f53ee6c 100644
--- a/arch/x86_64/kernel/setup.c
+++ b/arch/x86_64/kernel/setup.c
@@ -583,6 +583,10 @@ #endif
 	if (c->x86 == 15 && ((level >= 0x0f48 && level < 0x0f50) || level >= 0x0f58))
 		set_bit(X86_FEATURE_REP_GOOD, &c->x86_capability);

+	/* disable use of mwait on idle */
+	if (c->x86 == 16)
+		clear_bit(X86_FEATURE_MWAIT, c->x86_capability);
+
 	/* Enable workaround for FXSAVE leak */
 	if (c->x86 >= 6)
 		set_bit(X86_FEATURE_FXSAVE_LEAK, &c->x86_capability);

-
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