x86/mtrr: Add get_effective_type() service function

Add a service function for obtaining the effective cache mode of
overlapping MTRR registers.

Make use of that function in check_type_overlap().
Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Tested-by: Michael Kelley <mikelley@microsoft.com>
Link: https://lore.kernel.org/r/20230502120931.20719-11-jgross@suse.comSigned-off-by: Borislav Petkov (AMD) <bp@alien8.de>

arch/x86/kernel/cpu/mtrr/generic.c

@@ -80,31 +80,30 @@ static u64 get_mtrr_size(u64 mask)
 	return size;
 }
 
+static u8 get_effective_type(u8 type1, u8 type2)
+{
+	if (type1 == MTRR_TYPE_UNCACHABLE || type2 == MTRR_TYPE_UNCACHABLE)
+		return MTRR_TYPE_UNCACHABLE;
+
+	if ((type1 == MTRR_TYPE_WRBACK && type2 == MTRR_TYPE_WRTHROUGH) ||
+	    (type1 == MTRR_TYPE_WRTHROUGH && type2 == MTRR_TYPE_WRBACK))
+		return MTRR_TYPE_WRTHROUGH;
+
+	if (type1 != type2)
+		return MTRR_TYPE_UNCACHABLE;
+
+	return type1;
+}
+
 /*
  * Check and return the effective type for MTRR-MTRR type overlap.
- * Returns 1 if the effective type is UNCACHEABLE, else returns 0
+ * Returns true if the effective type is UNCACHEABLE, else returns false
  */
-static int check_type_overlap(u8 *prev, u8 *curr)
+static bool check_type_overlap(u8 *prev, u8 *curr)
 {
-	if (*prev == MTRR_TYPE_UNCACHABLE || *curr == MTRR_TYPE_UNCACHABLE) {
-		*prev = MTRR_TYPE_UNCACHABLE;
-		*curr = MTRR_TYPE_UNCACHABLE;
-		return 1;
-	}
-
-	if ((*prev == MTRR_TYPE_WRBACK && *curr == MTRR_TYPE_WRTHROUGH) ||
-	    (*prev == MTRR_TYPE_WRTHROUGH && *curr == MTRR_TYPE_WRBACK)) {
-		*prev = MTRR_TYPE_WRTHROUGH;
-		*curr = MTRR_TYPE_WRTHROUGH;
-	}
+	*prev = *curr = get_effective_type(*curr, *prev);
 
-	if (*prev != *curr) {
-		*prev = MTRR_TYPE_UNCACHABLE;
-		*curr = MTRR_TYPE_UNCACHABLE;
-		return 1;
-	}
-
-	return 0;
+	return *prev == MTRR_TYPE_UNCACHABLE;
 }
 
 /**