---

yaml
---
r: 109042
b: refs/heads/master
c: 8323444
h: refs/heads/master
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 28df82ebab79c6a2b4295dd94fd8de88196a49df
+refs/heads/master: 8323444b5dba3fe55e56a95d20d8f55c1d6745af

trunk/arch/x86/kernel/cpu/addon_cpuid_features.c

@@ -56,9 +56,22 @@ void __cpuinit validate_pat_support(struct cpuinfo_x86 *c)
 
 	switch (c->x86_vendor) {
 	case X86_VENDOR_INTEL:
-		if (c->x86 == 0xF || (c->x86 == 6 && c->x86_model >= 15))
+		/*
+		 * There is a known erratum on Pentium III and Core Solo
+		 * and Core Duo CPUs.
+		 * " Page with PAT set to WC while associated MTRR is UC
+		 *   may consolidate to UC "
+		 * Because of this erratum, it is better to stick with
+		 * setting WC in MTRR rather than using PAT on these CPUs.
+		 *
+		 * Enable PAT WC only on P4, Core 2 or later CPUs.
+		 */
+		if (c->x86 > 0x6 || (c->x86 == 6 && c->x86_model >= 15))
 			return;
-		break;
+
+		pat_disable("PAT WC disabled due to known CPU erratum.");
+		return;
+
 	case X86_VENDOR_AMD:
 	case X86_VENDOR_CENTAUR:
 	case X86_VENDOR_TRANSMETA: