[tip:x86/nuke386] x86, cleanups: Simplify sync_core() in the case of no CPUID

["tip-bot for H. Peter Anvin" <hpa@linux.intel.com>]

Commit-ID:  45c39fb0cc20d24da08d5bb159f57d191098104d
Gitweb:     http://git.kernel.org/tip/45c39fb0cc20d24da08d5bb159f57d191098104d
Author:     H. Peter Anvin <hpa@linux.intel.com>
AuthorDate: Wed, 28 Nov 2012 11:50:30 -0800
Committer:  H. Peter Anvin <hpa@linux.intel.com>
CommitDate: Thu, 29 Nov 2012 13:25:39 -0800

x86, cleanups: Simplify sync_core() in the case of no CPUID

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

[ v2: stylistic cleanup of the #else clause per suggestion by Borislav
  Petkov. ]

Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Link: http://lkml.kernel.org/r/1354132230-21854-9-git-send-email-hpa@linux.intel.com
Cc: Borislav Petkov <bp@alien8.de>
---
 arch/x86/include/asm/processor.h | 31 +++++++++++++++++++++----------
 1 file changed, 21 insertions(+), 10 deletions(-)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 9a4ee46..b0d3e73 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -673,17 +673,28 @@ 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,