[PATCH 01/12] KVM: x86: Add a framework for enabling KVM-governed x86 features

[Sean Christopherson]

Introduce yet another X86_FEATURE flag framework to manage and cache KVM
governed features (for lack of a better term).  "Governed" in this case
means that KVM has some level of involvement and/or vested interest in
whether or not an X86_FEATURE can be used by the guest.  The intent of the
framework is twofold: to simplify caching of guest CPUID flags that KVM
needs to frequently query, and to add clarity to such caching, e.g. it
isn't immediately obvious that SVM's bundle of flags for "optional nested]
SVM features" track whether or not a flag is exposed to L1.

Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
 arch/x86/include/asm/kvm_host.h  | 11 +++++++
 arch/x86/kvm/cpuid.c             |  2 ++
 arch/x86/kvm/cpuid.h             | 51 ++++++++++++++++++++++++++++++++
 arch/x86/kvm/governed_features.h |  9 ++++++
 4 files changed, 73 insertions(+)
 create mode 100644 arch/x86/kvm/governed_features.h

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 792a6037047a..cd660de02f7b 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -835,6 +835,17 @@ struct kvm_vcpu_arch {
 	struct kvm_cpuid_entry2 *cpuid_entries;
 	struct kvm_hypervisor_cpuid kvm_cpuid;
 
+	/*
+	 * Track whether or not the guest is allowed to use features that are
+	 * governed by KVM, where "governed" means KVM needs to manage state
+	 * and/or explicitly enable the feature in hardware.  Typically, but
+	 * not always, governed features can be used by the guest if and only
+	 * if both KVM and userspace want to expose the feature to the guest.
+	 */
+	struct {
+		u32 enabled;
+	} governed_features;
+
 	u64 reserved_gpa_bits;
 	int maxphyaddr;
 
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 8f8edeaf8177..013fdc27fc8f 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -335,6 +335,8 @@ static void kvm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
 	struct kvm_lapic *apic = vcpu->arch.apic;
 	struct kvm_cpuid_entry2 *best;
 
+	vcpu->arch.governed_features.enabled = 0;
+
 	best = kvm_find_cpuid_entry(vcpu, 1);
 	if (best && apic) {
 		if (cpuid_entry_has(best, X86_FEATURE_TSC_DEADLINE_TIMER))
diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h
index b1658c0de847..f61a2106ba90 100644
--- a/arch/x86/kvm/cpuid.h
+++ b/arch/x86/kvm/cpuid.h
@@ -232,4 +232,55 @@ static __always_inline bool guest_pv_has(struct kvm_vcpu *vcpu,
 	return vcpu->arch.pv_cpuid.features & (1u << kvm_feature);
 }
 
+enum kvm_governed_features {
+#define KVM_GOVERNED_FEATURE(x) KVM_GOVERNED_##x,
+#include "governed_features.h"
+	KVM_NR_GOVERNED_FEATURES
+};
+
+static __always_inline int kvm_governed_feature_index(unsigned int x86_feature)
+{
+	switch (x86_feature) {
+#define KVM_GOVERNED_FEATURE(x) case x: return KVM_GOVERNED_##x;
+#include "governed_features.h"
+	default:
+		return -1;
+	}
+}
+
+static __always_inline int kvm_is_governed_feature(unsigned int x86_feature)
+{
+	return kvm_governed_feature_index(x86_feature) >= 0;
+}
+
+static __always_inline u32 kvm_governed_feature_bit(unsigned int x86_feature)
+{
+	int index = kvm_governed_feature_index(x86_feature);
+
+	BUILD_BUG_ON(index < 0);
+	return BIT(index);
+}
+
+static __always_inline void kvm_governed_feature_set(struct kvm_vcpu *vcpu,
+						     unsigned int x86_feature)
+{
+	BUILD_BUG_ON(KVM_NR_GOVERNED_FEATURES >
+		     sizeof(vcpu->arch.governed_features.enabled) * BITS_PER_BYTE);
+
+	vcpu->arch.governed_features.enabled |= kvm_governed_feature_bit(x86_feature);
+}
+
+static __always_inline void kvm_governed_feature_check_and_set(struct kvm_vcpu *vcpu,
+							       unsigned int x86_feature)
+{
+	if (guest_cpuid_has(vcpu, x86_feature))
+		kvm_governed_feature_set(vcpu, x86_feature);
+}
+
+static __always_inline bool guest_can_use(struct kvm_vcpu *vcpu,
+					  unsigned int x86_feature)
+{
+	return vcpu->arch.governed_features.enabled & kvm_governed_feature_bit(x86_feature);
+}
+
 #endif
diff --git a/arch/x86/kvm/governed_features.h b/arch/x86/kvm/governed_features.h
new file mode 100644
index 000000000000..40ce8e6608cd
--- /dev/null
+++ b/arch/x86/kvm/governed_features.h
@@ -0,0 +1,9 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#if !defined(KVM_GOVERNED_FEATURE) || defined(KVM_GOVERNED_X86_FEATURE)
+BUILD_BUG()
+#endif
+
+#define KVM_GOVERNED_X86_FEATURE(x) KVM_GOVERNED_FEATURE(X86_FEATURE_##x)
+
+#undef KVM_GOVERNED_X86_FEATURE
+#undef KVM_GOVERNED_FEATURE
-- 
2.39.2.637.g21b0678d19-goog