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",