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authorvenkatesh.pallipadi@intel.com <venkatesh.pallipadi@intel.com>2008-08-20 16:45:53 -0700
committerIngo Molnar <mingo@elte.hu>2008-08-21 13:27:34 +0200
commit8323444b5dba3fe55e56a95d20d8f55c1d6745af (patch)
treee2d657ff43c768d3b9f47642fa522cba1c3ffcd8
parent28df82ebab79c6a2b4295dd94fd8de88196a49df (diff)
x86: PAT Update validate_pat_support for intel CPUs
Pentium III and Core Solo/Duo CPUs have an erratum " Page with PAT set to WC while associated MTRR is UC may consolidate to UC " which can result in WC setting in PAT to be ineffective. We will disable PAT on such CPUs, so that we can continue to use MTRR WC setting. Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
-rw-r--r--arch/x86/kernel/cpu/addon_cpuid_features.c17
1 files changed, 15 insertions, 2 deletions
diff --git a/arch/x86/kernel/cpu/addon_cpuid_features.c b/arch/x86/kernel/cpu/addon_cpuid_features.c
index 84a8220a607..a6ef672adbb 100644
--- a/arch/x86/kernel/cpu/addon_cpuid_features.c
+++ b/arch/x86/kernel/cpu/addon_cpuid_features.c
@@ -56,9 +56,22 @@ void __cpuinit validate_pat_support(struct cpuinfo_x86 *c)
switch (c->x86_vendor) {
case X86_VENDOR_INTEL:
- if (c->x86 == 0xF || (c->x86 == 6 && c->x86_model >= 15))
+ /*
+ * 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;
- break;
+
+ pat_disable("PAT WC disabled due to known CPU erratum.");
+ return;
+
case X86_VENDOR_AMD:
case X86_VENDOR_CENTAUR:
case X86_VENDOR_TRANSMETA: