x86/AMD: fold redundant parameters of cpu_has_amd_erratum()

The boolean 'osvw' indicator and 'osvw_id' can be folded - the function
can as well distinguish the non-OSVW case by checking for a negative
'osvw_id'. That way the whole variable argument list processing is only
needed on the legacy code path.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/arch/x86/cpu/amd.c
+++ b/xen/arch/x86/cpu/amd.c
@@ -186,7 +186,7 @@ static void __devinit set_cpuidmask(cons
  * Check for the presence of an AMD erratum. Arguments are defined in amd.h 
  * for each known erratum. Return 1 if erratum is found.
  */
-int cpu_has_amd_erratum(const struct cpuinfo_x86 *cpu, int osvw, ...) 
+int cpu_has_amd_erratum(const struct cpuinfo_x86 *cpu, int osvw_id, ...)
 {
 	va_list ap;
 	u32 range;
@@ -195,27 +195,24 @@ int cpu_has_amd_erratum(const struct cpu
 	if (cpu->x86_vendor != X86_VENDOR_AMD)
 		return 0;
 
-	va_start(ap, osvw);
+	if (osvw_id >= 0 && cpu_has(cpu, X86_FEATURE_OSVW)) {
+		u64 osvw_len;
 
-	if (osvw) {
-		u16 osvw_id = va_arg(ap, int);
+		rdmsrl(MSR_AMD_OSVW_ID_LENGTH, osvw_len);
 
-		if (cpu_has(cpu, X86_FEATURE_OSVW)) {
-			u64 osvw_len;
-			rdmsrl(MSR_AMD_OSVW_ID_LENGTH, osvw_len);
-
-			if (osvw_id < osvw_len) {
-				u64 osvw_bits;
-				rdmsrl(MSR_AMD_OSVW_STATUS + (osvw_id >> 6), 
-				       osvw_bits);
+		if (osvw_id < osvw_len) {
+			u64 osvw_bits;
 
-				va_end(ap);
-				return (osvw_bits >> (osvw_id & 0x3f)) & 0x01;
-			}
+			rdmsrl(MSR_AMD_OSVW_STATUS + (osvw_id >> 6),
+			       osvw_bits);
+
+			return (osvw_bits >> (osvw_id & 0x3f)) & 1;
 		}
 	}
 
 	/* OSVW unavailable or ID unknown, match family-model-stepping range */
+	va_start(ap, osvw_id);
+
 	ms = (cpu->x86_model << 4) | cpu->x86_mask;
 	while ((range = va_arg(ap, int))) {
 		if ((cpu->x86 == AMD_MODEL_RANGE_FAMILY(range)) &&
--- a/xen/include/asm-x86/amd.h
+++ b/xen/include/asm-x86/amd.h
@@ -119,8 +119,8 @@
  *   
  */
 
-#define AMD_LEGACY_ERRATUM(...)         0 /* legacy */, __VA_ARGS__, 0
-#define AMD_OSVW_ERRATUM(osvw_id, ...)  1 /* osvw */, osvw_id, __VA_ARGS__, 0
+#define AMD_LEGACY_ERRATUM(...)         -1 /* legacy */, __VA_ARGS__, 0
+#define AMD_OSVW_ERRATUM(osvw_id, ...)  osvw_id, __VA_ARGS__, 0
 #define AMD_MODEL_RANGE(f, m_start, s_start, m_end, s_end)              \
     ((f << 24) | (m_start << 16) | (s_start << 12) | (m_end << 4) | (s_end))
 #define AMD_MODEL_RANGE_FAMILY(range)   (((range) >> 24) & 0xff)