linux-kernel - [PATCH] x86, cpu: Fix X86_FEATURE

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Message-ID: <20101004073127.GA20305@liondog.tnic>
Date:	Mon, 4 Oct 2010 09:31:27 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	lkml <linux-kernel@...r.kernel.org>
Subject: [PATCH] x86, cpu: Fix X86_FEATURE_NOPL

ba0593bf553c450a03dbc5f8c1f0ff58b778a0c8 cleared the aforementioned
cpuid bit only on 32-bit due to various problems with Virtual PC. This
somehow got lost during the 32- + 64-bit merge so restore the feature
bit on 64-bit. For that, set it explicitly for non-constant arguments of
cpu_has(). Update comment for future reference.

Signed-off-by: Borislav Petkov <bp@...en8.de>
---
 arch/x86/kernel/cpu/common.c |   15 ++++++++++-----
 1 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index caa967d..4b68bda 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -704,16 +704,21 @@ void __init early_cpu_init(void)
 }
 
 /*
- * The NOPL instruction is supposed to exist on all CPUs with
- * family >= 6; unfortunately, that's not true in practice because
- * of early VIA chips and (more importantly) broken virtualizers that
- * are not easy to detect.  In the latter case it doesn't even *fail*
- * reliably, so probing for it doesn't even work.  Disable it completely
+ * The NOPL instruction is supposed to exist on all CPUs of family >= 6;
+ * unfortunately, that's not true in practice because of early VIA
+ * chips and (more importantly) broken virtualizers that are not easy
+ * to detect. In the latter case it doesn't even *fail* reliably, so
+ * probing for it doesn't even work. Disable it completely on 32-bit
  * unless we can find a reliable way to detect all the broken cases.
+ * Enable it explicitly on 64-bit for non-constant inputs of cpu_has().
  */
 static void __cpuinit detect_nopl(struct cpuinfo_x86 *c)
 {
+#ifdef CONFIG_X86_32
 	clear_cpu_cap(c, X86_FEATURE_NOPL);
+#else
+	set_cpu_cap(c, X86_FEATURE_NOPL);
+#endif
 }
 
 static void __cpuinit generic_identify(struct cpuinfo_x86 *c)
-- 
1.7.2.3

-- 
Regards/Gruss,
    Boris.
--
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