i386: Replace broken serialize_cpu in microcode driver with correct sync_core

Passing random input values in eax to cpuid is not a good idea
because the CPU will GPF for unknown ones.
Use the correct x86-64 version that exists for a longer time too.
This also adds a memory barrier to prevent the optimizer from
reordering. 

Cc: tigran@veritas.com

Signed-off-by: Andi Kleen <ak@suse.de>

Index: linux/arch/i386/kernel/microcode.c
===================================================================
--- linux.orig/arch/i386/kernel/microcode.c
+++ linux/arch/i386/kernel/microcode.c
@@ -165,7 +165,7 @@ static void collect_cpu_info (void *unus
 
 	wrmsr(MSR_IA32_UCODE_REV, 0, 0);
 	/* see notes above for revision 1.07.  Apparent chip bug */
-	serialize_cpu();
+	sync_core();
 	/* get the current revision from MSR 0x8B */
 	rdmsr(MSR_IA32_UCODE_REV, val[0], uci->rev);
 	pr_debug("microcode: collect_cpu_info : sig=0x%x, pf=0x%x, rev=0x%x\n",
@@ -379,7 +379,7 @@ static void do_update_one (void * unused
 	wrmsr(MSR_IA32_UCODE_REV, 0, 0);
 
 	/* see notes above for revision 1.07.  Apparent chip bug */
-	serialize_cpu();
+	sync_core();
 
 	/* get the current revision from MSR 0x8B */
 	rdmsr(MSR_IA32_UCODE_REV, val[0], val[1]);
Index: linux/include/asm-i386/processor.h
===================================================================
--- linux.orig/include/asm-i386/processor.h
+++ linux/include/asm-i386/processor.h
@@ -281,9 +281,11 @@ static inline void clear_in_cr4 (unsigne
 	outb((data), 0x23); \
 } while (0)
 
-static inline void serialize_cpu(void)
+/* Stop speculative execution */
+static inline void sync_core(void)
 {
-	 __asm__ __volatile__ ("cpuid" : : : "ax", "bx", "cx", "dx");
+	int tmp;
+	asm volatile("cpuid" : "=a" (tmp) : "0" (1) : "ebx","ecx","edx","memory");
 }
 
 static inline void __monitor(const void *eax, unsigned long ecx,