x86: handle PAT more like other CPU features

Impact: Cleanup

When PAT was originally introduced, it was handled specially for a few
reasons:

- PAT bugs are hard to track down, so we wanted to maintain a
  whitelist of CPUs.
- The i386 and x86-64 CPUID code was not yet unified.

Both of these are now obsolete, so handle PAT like any other features,
including ordinary feature blacklisting due to known bugs.
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

arch/x86/include/asm/pat.h

@@ -5,10 +5,8 @@
 
 #ifdef CONFIG_X86_PAT
 extern int pat_enabled;
-extern void validate_pat_support(struct cpuinfo_x86 *c);
 #else
 static const int pat_enabled;
-static inline void validate_pat_support(struct cpuinfo_x86 *c) { }
 #endif
 
 extern void pat_init(void);
@@ -17,6 +15,4 @@ extern int reserve_memtype(u64 start, u64 end,
 		unsigned long req_type, unsigned long *ret_type);
 extern int free_memtype(u64 start, u64 end);
 
-extern void pat_disable(char *reason);
-
 #endif /* _ASM_X86_PAT_H */

arch/x86/kernel/cpu/addon_cpuid_features.c

@@ -143,37 +143,3 @@ void __cpuinit detect_extended_topology(struct cpuinfo_x86 *c)
 	return;
 #endif
 }
-
-#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:
-		/*
-		 * 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;
-
-		pat_disable("PAT WC disabled due to known CPU erratum.");
-		return;
-
-	case X86_VENDOR_AMD:
-	case X86_VENDOR_CENTAUR:
-	case X86_VENDOR_TRANSMETA:
-		return;
-	}
-
-	pat_disable("PAT disabled. Not yet verified on this CPU type.");
-}
-#endif

arch/x86/kernel/cpu/common.c

@@ -570,8 +570,6 @@ static void __init early_identify_cpu(struct cpuinfo_x86 *c)
 	if (this_cpu->c_early_init)
 		this_cpu->c_early_init(c);
 
-	validate_pat_support(c);
-
 #ifdef CONFIG_SMP
 	c->cpu_index = boot_cpu_id;
 #endif

arch/x86/kernel/cpu/intel.c

@@ -50,6 +50,18 @@ static void __cpuinit early_init_intel(struct cpuinfo_x86 *c)
 		set_cpu_cap(c, X86_FEATURE_NONSTOP_TSC);
 	}
 
+	/*
+	 * 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 == 6 && c->x86_model < 15)
+		clear_cpu_cap(c, X86_FEATURE_PAT);
 }
 
 #ifdef CONFIG_X86_32

arch/x86/mm/pat.c

@@ -30,7 +30,7 @@
 #ifdef CONFIG_X86_PAT
 int __read_mostly pat_enabled = 1;
 
-void __cpuinit pat_disable(char *reason)
+void __cpuinit pat_disable(const char *reason)
 {
 	pat_enabled = 0;
 	printk(KERN_INFO "%s\n", reason);
@@ -42,6 +42,11 @@ static int __init nopat(char *str)
 	return 0;
 }
 early_param("nopat", nopat);
+#else
+static inline void pat_disable(const char *reason)
+{
+	(void)reason;
+}
 #endif
 
 
@@ -78,16 +83,20 @@ void pat_init(void)
 	if (!pat_enabled)
 		return;
 
-	/* Paranoia check. */
-	if (!cpu_has_pat && boot_pat_state) {
-		/*
-		 * If this happens we are on a secondary CPU, but
-		 * switched to PAT on the boot CPU. We have no way to
-		 * undo PAT.
-		 */
-		printk(KERN_ERR "PAT enabled, "
-		       "but not supported by secondary CPU\n");
-		BUG();
+	if (!cpu_has_pat) {
+		if (!boot_pat_state) {
+			pat_disable("PAT not supported by CPU.");
+			return;
+		} else {
+			/*
+			 * If this happens we are on a secondary CPU, but
+			 * switched to PAT on the boot CPU. We have no way to
+			 * undo PAT.
+			 */
+			printk(KERN_ERR "PAT enabled, "
+			       "but not supported by secondary CPU\n");
+			BUG();
+		}
 	}
 
 	/* Set PWT to Write-Combining. All other bits stay the same */