x86: PAT: fix ambiguous paranoia check in pat_init()

Starting with commit 8d4a4300854f3971502e81dacd930704cb88f606 (x86:
cleanup PAT cpu validation) the PAT CPU feature flag is not cleared
anymore. Now the error message

  "PAT enabled, but CPU feature cleared"

in pat_init() is misleading.

Furthermore the current code does not check for existence of the PAT
CPU feature flag if a CPU is whitelisted in validate_pat_support.

This patch clears pat_wc_enabled if boot CPU has no PAT feature flag
and adapts the paranoia check.

Signed-off-by: Andreas Herrmann <andreas.herrmann3@amd.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/cpu/addon_cpuid_features.c

@@ -53,6 +53,9 @@ void __cpuinit init_scattered_cpuid_features(struct cpuinfo_x86 *c)
 #ifdef CONFIG_X86_PAT
 void __cpuinit validate_pat_support(struct cpuinfo_x86 *c)
 {
+	if (!cpu_has_pat)
+		pat_disable("PAT not supported by CPU.");
+
 	switch (c->x86_vendor) {
 	case X86_VENDOR_INTEL:
 		if (c->x86 == 0xF || (c->x86 == 6 && c->x86_model >= 15))
@@ -64,8 +67,6 @@ void __cpuinit validate_pat_support(struct cpuinfo_x86 *c)
 		return;
 	}
 
-	pat_disable(cpu_has_pat ?
-		    "PAT disabled. Not yet verified on this CPU type." :
-		    "PAT not supported by CPU.");
+	pat_disable("PAT disabled. Not yet verified on this CPU type.");
 }
 #endif

arch/x86/mm/pat.c

@@ -76,14 +76,15 @@ void pat_init(void)
 		return;
 
 	/* Paranoia check. */
-	if (!cpu_has_pat) {
-		printk(KERN_ERR "PAT enabled, but CPU feature cleared\n");
+	if (!cpu_has_pat && boot_pat_state) {
 		/*
-		 * Panic if this happens on the secondary CPU, and we
+		 * If this happens we are on a secondary CPU, but
 		 * switched to PAT on the boot CPU. We have no way to
 		 * undo PAT.
-		*/
-		BUG_ON(boot_pat_state);
+		 */
+		printk(KERN_ERR "PAT enabled, "
+		       "but not supported by secondary CPU\n");
+		BUG();
 	}
 
 	/* Set PWT to Write-Combining. All other bits stay the same */