[Xen-devel] [PATCH v2 2/3] x86 Test and expose CPUID faulting capabilities in /proc/cpuinfo

[Kyle Huey <me@xxxxxxxxxxxx>]

Xen advertises the underlying support for CPUID faulting but not does pass
through writes to the relevant MSR, nor does it virtualize it, so it does
not actually work. For now mask off the relevant bit on MSR_PLATFORM_INFO.

Signed-off-by: Kyle Huey <khuey@xxxxxxxxxxxx>
---
 arch/x86/include/asm/cpufeatures.h |  1 +
 arch/x86/include/asm/msr-index.h   |  1 +
 arch/x86/kernel/cpu/scattered.c    | 14 ++++++++++++++
 arch/x86/xen/enlighten.c           |  3 +++
 4 files changed, 19 insertions(+)

diff --git a/arch/x86/include/asm/cpufeatures.h 
b/arch/x86/include/asm/cpufeatures.h
index 92a8308..78b9d06 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -190,6 +190,7 @@
 
 #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_CPUID_FAULT ( 7*32+ 4) /* Intel CPUID faulting */
 
 #define X86_FEATURE_HW_PSTATE  ( 7*32+ 8) /* AMD HW-PState */
 #define X86_FEATURE_PROC_FEEDBACK ( 7*32+ 9) /* AMD ProcFeedbackInterface */
diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index 56f4c66..83908d5 100644
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -41,6 +41,7 @@
 #define MSR_IA32_PERFCTR1              0x000000c2
 #define MSR_FSB_FREQ                   0x000000cd
 #define MSR_PLATFORM_INFO              0x000000ce
+#define CPUID_FAULTING_SUPPORT         (1UL << 31)
 
 #define MSR_NHM_SNB_PKG_CST_CFG_CTL    0x000000e2
 #define NHM_C3_AUTO_DEMOTE             (1UL << 25)
diff --git a/arch/x86/kernel/cpu/scattered.c b/arch/x86/kernel/cpu/scattered.c
index 8cb57df..d502da1 100644
--- a/arch/x86/kernel/cpu/scattered.c
+++ b/arch/x86/kernel/cpu/scattered.c
@@ -24,6 +24,17 @@ enum cpuid_regs {
        CR_EBX
 };
 
+static int supports_cpuid_faulting(void)
+{
+       unsigned int lo, hi;
+
+       if (rdmsr_safe(MSR_PLATFORM_INFO, &lo, &hi) == 0 &&
+           (lo & CPUID_FAULTING_SUPPORT))
+               return 1;
+       else
+               return 0;
+}
+
 void init_scattered_cpuid_features(struct cpuinfo_x86 *c)
 {
        u32 max_level;
@@ -54,4 +65,7 @@ void init_scattered_cpuid_features(struct cpuinfo_x86 *c)
                if (regs[cb->reg] & (1 << cb->bit))
                        set_cpu_cap(c, cb->feature);
        }
+
+       if (supports_cpuid_faulting())
+               set_cpu_cap(c, X86_FEATURE_CPUID_FAULT);
 }
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index b86ebb1..2c47f0c 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -1050,6 +1050,9 @@ static u64 xen_read_msr_safe(unsigned int msr, int *err)
 #endif
                        val &= ~X2APIC_ENABLE;
                break;
+       case MSR_PLATFORM_INFO:
+               val &= ~CPUID_FAULTING_SUPPORT;
+               break;
        }
        return val;
 }
-- 
2.7.4


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