linux-kernel - [PATCH 8/8] x86, cleanups: Simplify sync

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Date:	Wed, 28 Nov 2012 11:50:30 -0800
From:	"H. Peter Anvin" <hpa@...ux.intel.com>
To:	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Mario Gzuk <mariogzuk@...hnikz.de>,
	"H. Peter Anvin" <hpa@...ux.intel.com>
Subject: [PATCH 8/8] x86, cleanups: Simplify sync_core() in the case of no CPUID

From: "H. Peter Anvin" <hpa@...ux.intel.com>

Simplify the implementation of sync_core() for the case where we may
not have the CPUID instruction available.

Signed-off-by: H. Peter Anvin <hpa@...ux.intel.com>
---
 arch/x86/include/asm/processor.h | 27 +++++++++++++++++----------
 1 file changed, 17 insertions(+), 10 deletions(-)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 9a4ee46..b381df7 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -673,17 +673,24 @@ static inline void sync_core(void)
 	int tmp;
 
 #ifdef CONFIG_M486
-	if (boot_cpu_data.x86 < 5)
-		/* There is no speculative execution.
-		 * jmp is a barrier to prefetching. */
-		asm volatile("jmp 1f\n1:\n" ::: "memory");
-	else
+	/*
+	 * Do a CPUID if available, otherwise do a jump.  The jump
+	 * can conveniently enough be the jump around CPUID.
+	 */
+	asm volatile("cmpl %2,%1\n\t"
+		     "jl 1f\n\t"
+		     "cpuid\n"
+		     "1:"
+		     : "=a" (tmp)
+		     : "rm" (boot_cpu_data.cpuid_level), "ri" (0), "0" (1)
+		     : "ebx", "ecx", "edx", "memory");
+#else
+	/* cpuid is a barrier to speculative execution.
+	 * Prefetched instructions are automatically
+	 * invalidated when modified. */
+	asm volatile("cpuid" : "=a" (tmp) : "0" (1)
+		     : "ebx", "ecx", "edx", "memory");
 #endif
-		/* cpuid is a barrier to speculative execution.
-		 * Prefetched instructions are automatically
-		 * invalidated when modified. */
-		asm volatile("cpuid" : "=a" (tmp) : "0" (1)
-			     : "ebx", "ecx", "edx", "memory");
 }
 
 static inline void __monitor(const void *eax, unsigned long ecx,
-- 
1.7.11.7

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