[PATCH v13 5/8] x86/cpufeature: Detect CPUID faulting support

From: Kyle Huey
Date: Sun Nov 27 2016 - 22:08:25 EST


Intel supports faulting on the CPUID instruction beginning with Ivy Bridge.
When enabled, the processor will fault on attempts to execute the CPUID
instruction with CPL>0. This will allow a ptracer to emulate the CPUID
instruction.

Bit 31 of MSR_PLATFORM_INFO advertises support for this feature. It is
documented in detail in Section 2.3.2 of
https://bugzilla.kernel.org/attachment.cgi?id=243991

Detect support for this feature and expose it as X86_FEATURE_CPUID_FAULT.

Signed-off-by: Kyle Huey <khuey@xxxxxxxxxxxx>
Reviewed-by: Borislav Petkov <bp@xxxxxxx>
---
arch/x86/include/asm/cpufeatures.h | 1 +
arch/x86/include/asm/msr-index.h | 2 ++
arch/x86/kernel/cpu/intel.c | 12 ++++++++++++
3 files changed, 15 insertions(+)

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index a396292..85f853f 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -182,16 +182,17 @@

/*
* Auxiliary flags: Linux defined - For features scattered in various
* CPUID levels like 0x6, 0xA etc, word 7.
*
* Reuse free bits when adding new feature flags!
*/

+#define X86_FEATURE_CPUID_FAULT ( 7*32+ 0) /* Intel CPUID faulting */
#define X86_FEATURE_CPB ( 7*32+ 2) /* AMD Core Performance Boost */
#define X86_FEATURE_EPB ( 7*32+ 3) /* IA32_ENERGY_PERF_BIAS support */

#define X86_FEATURE_HW_PSTATE ( 7*32+ 8) /* AMD HW-PState */
#define X86_FEATURE_PROC_FEEDBACK ( 7*32+ 9) /* AMD ProcFeedbackInterface */

#define X86_FEATURE_INTEL_PT ( 7*32+15) /* Intel Processor Trace */
#define X86_FEATURE_AVX512_4VNNIW (7*32+16) /* AVX-512 Neural Network Instructions */
diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index 78f3760..3ac0acf 100644
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -36,16 +36,18 @@
#define EFER_LMSLE (1<<_EFER_LMSLE)
#define EFER_FFXSR (1<<_EFER_FFXSR)

/* Intel MSRs. Some also available on other CPUs */
#define MSR_IA32_PERFCTR0 0x000000c1
#define MSR_IA32_PERFCTR1 0x000000c2
#define MSR_FSB_FREQ 0x000000cd
#define MSR_PLATFORM_INFO 0x000000ce
+#define MSR_PLATFORM_INFO_CPUID_FAULT_BIT 31
+#define MSR_PLATFORM_INFO_CPUID_FAULT BIT_ULL(MSR_PLATFORM_INFO_CPUID_FAULT_BIT)

#define MSR_NHM_SNB_PKG_CST_CFG_CTL 0x000000e2
#define NHM_C3_AUTO_DEMOTE (1UL << 25)
#define NHM_C1_AUTO_DEMOTE (1UL << 26)
#define ATM_LNC_C6_AUTO_DEMOTE (1UL << 25)
#define SNB_C1_AUTO_UNDEMOTE (1UL << 27)
#define SNB_C3_AUTO_UNDEMOTE (1UL << 28)

diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index fcd484d..12ddddf 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -447,16 +447,26 @@ static void intel_bsp_resume(struct cpuinfo_x86 *c)
{
/*
* MSR_IA32_ENERGY_PERF_BIAS is lost across suspend/resume,
* so reinitialize it properly like during bootup:
*/
init_intel_energy_perf(c);
}

+static void init_intel_misc_features(struct cpuinfo_x86 *c)
+{
+ u64 msr;
+
+ if (!rdmsrl_safe(MSR_PLATFORM_INFO, &msr)) {
+ if (msr & MSR_PLATFORM_INFO_CPUID_FAULT)
+ set_cpu_cap(c, X86_FEATURE_CPUID_FAULT);
+ }
+}
+
static void init_intel(struct cpuinfo_x86 *c)
{
unsigned int l2 = 0;

early_init_intel(c);

intel_workarounds(c);

@@ -560,16 +570,18 @@ static void init_intel(struct cpuinfo_x86 *c)

/* Work around errata */
srat_detect_node(c);

if (cpu_has(c, X86_FEATURE_VMX))
detect_vmx_virtcap(c);

init_intel_energy_perf(c);
+
+ init_intel_misc_features(c);
}

#ifdef CONFIG_X86_32
static unsigned int intel_size_cache(struct cpuinfo_x86 *c, unsigned int size)
{
/*
* Intel PIII Tualatin. This comes in two flavours.
* One has 256kb of cache, the other 512. We have no way
--
2.10.2