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Date: Sat, 08 Aug 2009 20:17:43 -0300
From: Kevin Winchester <kjwinchester@...il.com>
To: Borislav Petkov <petkovbb@...glemail.com>,
Kevin Winchester <kjwinchester@...il.com>,
Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
Thomas Gleixner <tglx@...utronix.de>,
Yinghai Lu <yinghai@...nel.org>,
Andreas Herrmann <andreas.herrmann3@....com>,
LKML <linux-kernel@...r.kernel.org>, borislav.petkov@....com
Subject: [PATCH v2] x86: clear incorrectly forced X86_FEATURE_LAHF_LM flag
Due to an erratum with certain AMD Athlon 64 processors, the BIOS may
need to force enable the LAHF_LM capability. Unfortunately, in at
least one case, the BIOS does this even for processors that do not
support the functionality.
Add a specific check that will clear the feature bit for processors
known not to support the LAHF/SAHF instructions.
Signed-off-by: Kevin Winchester <kjwinchester@...il.com>
---
arch/x86/kernel/cpu/amd.c | 8 ++++++++
1 files changed, 8 insertions(+), 0 deletions(-)
diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index e2485b0..7b52787 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -400,6 +400,14 @@ static void __cpuinit init_amd(struct cpuinfo_x86 *c)
level = cpuid_eax(1);
if((level >= 0x0f48 && level < 0x0f50) || level >= 0x0f58)
set_cpu_cap(c, X86_FEATURE_REP_GOOD);
+
+ /*
+ * Some BIOSes incorrectly set this feature, but only Revisions
+ * D (Extended Model = 1) and E (Extended Model = 2) actually
+ * support it.
+ */
+ if (!(level & 0x00030000))
+ clear_cpu_cap(c, X86_FEATURE_LAHF_LM);
}
if (c->x86 == 0x10 || c->x86 == 0x11)
set_cpu_cap(c, X86_FEATURE_REP_GOOD);
--
1.6.4
--
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