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>

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 9a4ee46..b0d3e73 100644 (file)
--- 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,