Add yet another CPUID macro, this time for features that the host kernel
synthesizes into boot_cpu_data, i.e. that the kernel force sets even in
situations where the feature isn't reported by CPUID. Thanks to the
macro shenanigans of kvm_cpu_cap_init(), such features can now be handled
in the core CPUID framework, i.e. don't need to be handled out-of-band and
thus without as many guardrails.
Adding a dedicated macro also helps document what's going on, e.g. the
calls to kvm_cpu_cap_check_and_set() are very confusing unless the reader
knows exactly how kvm_cpu_cap_init() generates kvm_cpu_caps (and even
then, it's far from obvious).
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
arch/x86/kvm/cpuid.c | 49 +++++++++++++++++++++++++++-----------------
1 file changed, 30 insertions(+), 19 deletions(-)
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 8d088a888a0d..2b05a7e61994 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -665,6 +665,7 @@ do { \
const struct cpuid_reg cpuid = x86_feature_cpuid(leaf * 32); \
const u32 __maybe_unused kvm_cpu_cap_init_in_progress = leaf; \
u32 kvm_cpu_cap_passthrough = 0; \
+ u32 kvm_cpu_cap_synthesized = 0; \
u32 kvm_cpu_cap_emulated = 0; \
\
if (leaf < NCAPINTS) \
@@ -673,7 +674,8 @@ do { \
kvm_cpu_caps[leaf] = (mask); \
\
kvm_cpu_caps[leaf] |= kvm_cpu_cap_passthrough; \
- kvm_cpu_caps[leaf] &= raw_cpuid_get(cpuid); \
+ kvm_cpu_caps[leaf] &= (raw_cpuid_get(cpuid) | \
+ kvm_cpu_cap_synthesized); \
kvm_cpu_caps[leaf] |= kvm_cpu_cap_emulated; \
} while (0)
@@ -720,6 +722,17 @@ do { \
F(name); \
})
+/*
+ * Synthesized Feature - For features that are synthesized into boot_cpu_data,
+ * i.e. may not be present in the raw CPUID, but can still be advertised to
+ * userspace. Primarily used for mitigation related feature flags.
+ */
+#define SYNTHESIZED_F(name) \
+({ \
+ kvm_cpu_cap_synthesized |= F(name); \
+ F(name); \
+})
+
/*
* Passthrough Feature - For features that KVM supports based purely on raw
* hardware CPUID, i.e. that KVM virtualizes even if the host kernel doesn't
@@ -1084,35 +1097,32 @@ void kvm_set_cpu_caps(void)
kvm_cpu_cap_init(CPUID_8000_0021_EAX,
F(NO_NESTED_DATA_BP) |
- F(LFENCE_RDTSC) |
+ /*
+ * Synthesize "LFENCE is serializing" into the AMD-defined entry
+ * in KVM's supported CPUID, i.e. if the feature is reported as
+ * supported by the kernel. LFENCE_RDTSC was a Linux-defined
+ * synthetic feature long before AMD joined the bandwagon, e.g.
+ * LFENCE is serializing on most CPUs that support SSE2. On
+ * CPUs that don't support AMD's leaf, ANDing with the raw host
+ * CPUID will drop the flags, and reporting support in AMD's
+ * leaf can make it easier for userspace to detect the feature.
+ */
+ SYNTHESIZED_F(LFENCE_RDTSC) |
0 /* SmmPgCfgLock */ |
F(NULL_SEL_CLR_BASE) |
F(AUTOIBRS) |
EMULATED_F(NO_SMM_CTL_MSR) |
0 /* PrefetchCtlMsr */ |
- F(WRMSR_XX_BASE_NS)
+ F(WRMSR_XX_BASE_NS) |
+ SYNTHESIZED_F(SBPB) |
+ SYNTHESIZED_F(IBPB_BRTYPE) |
+ SYNTHESIZED_F(SRSO_NO)
);
- kvm_cpu_cap_check_and_set(X86_FEATURE_SBPB);
- kvm_cpu_cap_check_and_set(X86_FEATURE_IBPB_BRTYPE);
- kvm_cpu_cap_check_and_set(X86_FEATURE_SRSO_NO);
-
kvm_cpu_cap_init(CPUID_8000_0022_EAX,
F(PERFMON_V2)
);
- /*
- * Synthesize "LFENCE is serializing" into the AMD-defined entry in
- * KVM's supported CPUID if the feature is reported as supported by the
- * kernel. LFENCE_RDTSC was a Linux-defined synthetic feature long
- * before AMD joined the bandwagon, e.g. LFENCE is serializing on most
- * CPUs that support SSE2. On CPUs that don't support AMD's leaf,
- * kvm_cpu_cap_init() will unfortunately drop the flag due to ANDing
- * the mask with the raw host CPUID, and reporting support in AMD's
- * leaf can make it easier for userspace to detect the feature.
- */
- if (cpu_feature_enabled(X86_FEATURE_LFENCE_RDTSC))
- kvm_cpu_cap_set(X86_FEATURE_LFENCE_RDTSC);
if (!static_cpu_has_bug(X86_BUG_NULL_SEG))
kvm_cpu_cap_set(X86_FEATURE_NULL_SEL_CLR_BASE);
@@ -1150,6 +1160,7 @@ EXPORT_SYMBOL_GPL(kvm_set_cpu_caps);
#undef SF
#undef X86_64_F
#undef EMULATED_F
+#undef SYNTHESIZED_F
#undef PASSTHROUGH_F
#undef ALIASED_1_EDX_F
--
2.47.0.338.g60cca15819-goog
