x86: cleanup PAT cpu validation

Move the scattered checks for PAT support to a single function. Its
moved to addon_cpuid_features.c as this file is shared between 32 and
64 bit.

Remove the manipulation of the PAT feature bit and just disable PAT in
the PAT layer, based on the PAT bit provided by the CPU and the
current CPU version/model white list.

Change the boot CPU check so it works on Voyager somewhere in the
future as well :) Also panic, when a secondary has PAT disabled but
the primary one has alrady switched to PAT. We have no way to undo
that.

The white list is kept for now to ensure that we can rely on known to
work CPU types and concentrate on the software induced problems
instead of fighthing CPU erratas and subtle wreckage caused by not yet
verified CPUs. Once the PAT code has stabilized enough, we can remove
the white list and open the can of worms.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 22 insertions, 28 deletions

diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
index 277446cd30b6..60adbe22efa0 100644
--- a/arch/x86/mm/pat.c
+++ b/arch/x86/mm/pat.c
@@ -25,31 +25,24 @@
 #include <asm/mtrr.h>
 #include <asm/io.h>
 
-int pat_wc_enabled = 1;
+#ifdef CONFIG_X86_PAT
+int __read_mostly pat_wc_enabled = 1;
 
-static u64 __read_mostly boot_pat_state;
-
-static int nopat(char *str)
+void __init pat_disable(char *reason)
 {
 	pat_wc_enabled = 0;
-	printk(KERN_INFO "x86: PAT support disabled.\n");
-
-	return 0;
+	printk(KERN_INFO "%s\n", reason);
 }
-early_param("nopat", nopat);
 
-static int pat_known_cpu(void)
+static int nopat(char *str)
 {
-	if (!pat_wc_enabled)
-		return 0;
-
-	if (cpu_has_pat)
-		return 1;
-
-	pat_wc_enabled = 0;
-	printk(KERN_INFO "CPU and/or kernel does not support PAT.\n");
+	pat_disable("PAT support disabled.");
 	return 0;
 }
+early_param("nopat", nopat);
+#endif
+
+static u64 __read_mostly boot_pat_state;
 
 enum {
 	PAT_UC = 0,		/* uncached */
@@ -66,17 +59,19 @@ void pat_init(void)
 {
 	u64 pat;
 
-#ifndef CONFIG_X86_PAT
-	nopat(NULL);
-#endif
-
-	/* Boot CPU enables PAT based on CPU feature */
-	if (!smp_processor_id() && !pat_known_cpu())
+	if (!pat_wc_enabled)
 		return;
 
-	/* APs enable PAT iff boot CPU has enabled it before */
-	if (smp_processor_id() && !pat_wc_enabled)
-		return;
+	/* Paranoia check. */
+	if (!cpu_has_pat) {
+		printk(KERN_ERR "PAT enabled, but CPU feature cleared\n");
+		/*
+		 * Panic if this happens on the secondary CPU, and we
+		 * switched to PAT on the boot CPU. We have no way to
+		 * undo PAT.
+		*/
+		BUG_ON(boot_pat_state);
+	}
 
 	/* Set PWT to Write-Combining. All other bits stay the same */
 	/*
@@ -95,9 +90,8 @@ void pat_init(void)
 	      PAT(4,WB) | PAT(5,WC) | PAT(6,UC_MINUS) | PAT(7,UC);
 
 	/* Boot CPU check */
-	if (!smp_processor_id()) {
+	if (!boot_pat_state)
 		rdmsrl(MSR_IA32_CR_PAT, boot_pat_state);
-	}
 
 	wrmsrl(MSR_IA32_CR_PAT, pat);
 	printk(KERN_INFO "x86 PAT enabled: cpu %d, old 0x%Lx, new 0x%Lx\n",