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>

1 files changed, 20 insertions, 11 deletions

diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
index 8b08fb955274..430cb44dd3f4 100644
--- a/arch/x86/mm/pat.c
+++ b/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 */