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, 12 insertions, 0 deletions

diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index 8ea6929e974c..20ce03acf04b 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/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