Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
tjh.dev
kernel
os
linux
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>
authored by venkatesh.pallipadi@intel.com and committed by Ingo Molnar 8323444b 28df82eb
+15
-2
arch/x86/kernel/cpu/addon_cpuid_features.c
+15
-2
arch/x86/kernel/cpu/addon_cpuid_features.c
···
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switch (c->x86_vendor) {
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case X86_VENDOR_INTEL:
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-
if (c->x86 == 0xF || (c->x86 == 6 && c->x86_model >= 15))
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+
/*
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* There is a known erratum on Pentium III and Core Solo
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* and Core Duo CPUs.
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* " Page with PAT set to WC while associated MTRR is UC
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* may consolidate to UC "
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* Because of this erratum, it is better to stick with
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* setting WC in MTRR rather than using PAT on these CPUs.
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*
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* Enable PAT WC only on P4, Core 2 or later CPUs.
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*/
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if (c->x86 > 0x6 || (c->x86 == 6 && c->x86_model >= 15))
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return;
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-
break;
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+
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pat_disable("PAT WC disabled due to known CPU erratum.");
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return;
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+
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case X86_VENDOR_AMD:
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case X86_VENDOR_CENTAUR:
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case X86_VENDOR_TRANSMETA: