[RFC PATCH v2 06/11] KVM: x86: Advertise ARCH_CAP_VIRTUAL_ENUM support

[Chao Gao]

From: Zhang Chen <chen.zhang@xxxxxxxxx>

Bit 63 of IA32_ARCH_CAPABILITIES MSR indicates availablility of the
VIRTUAL_ENUMERATION_MSR (index 0x50000000) that enumerates features like
e.g., mitigation enumeration which is used for guest to hint VMMs the
software mitigations in use.

Advertise ARCH_CAP_VIRTUAL_ENUM support for VMX and emulate read/write
of the VIRTUAL_ENUMERATION_MSR. Now VIRTUAL_ENUMERATION_MSR is always 0.

Signed-off-by: Zhang Chen <chen.zhang@xxxxxxxxx>
Co-developed-by: Chao Gao <chao.gao@xxxxxxxxx>
Signed-off-by: Chao Gao <chao.gao@xxxxxxxxx>
Tested-by: Jiaan Lu <jiaan.lu@xxxxxxxxx>
---
 arch/x86/kvm/svm/svm.c |  1 +
 arch/x86/kvm/vmx/vmx.c | 19 +++++++++++++++++++
 arch/x86/kvm/vmx/vmx.h |  1 +
 arch/x86/kvm/x86.c     | 16 +++++++++++++++-
 4 files changed, 36 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 57f241c5a371..195d0cf9309a 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -4093,6 +4093,7 @@ static bool svm_has_emulated_msr(struct kvm *kvm, u32 index)
 {
 	switch (index) {
 	case MSR_IA32_MCG_EXT_CTL:
+	case MSR_VIRTUAL_ENUMERATION:
 	case MSR_IA32_VMX_BASIC ... MSR_IA32_VMX_VMFUNC:
 		return false;
 	case MSR_IA32_SMBASE:
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 9f6919bec2b3..85419137decb 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -1943,6 +1943,8 @@ static inline bool is_vmx_feature_control_msr_valid(struct vcpu_vmx *vmx,
 	return !(msr->data & ~valid_bits);
 }
 
+#define VIRTUAL_ENUMERATION_VALID_BITS	0ULL
+
 static int vmx_get_msr_feature(struct kvm_msr_entry *msr)
 {
 	switch (msr->index) {
@@ -1950,6 +1952,9 @@ static int vmx_get_msr_feature(struct kvm_msr_entry *msr)
 		if (!nested)
 			return 1;
 		return vmx_get_vmx_msr(&vmcs_config.nested, msr->index, &msr->data);
+	case MSR_VIRTUAL_ENUMERATION:
+		msr->data = VIRTUAL_ENUMERATION_VALID_BITS;
+		return 0;
 	default:
 		return KVM_MSR_RET_INVALID;
 	}
@@ -2096,6 +2101,12 @@ static int vmx_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 	case MSR_IA32_DEBUGCTLMSR:
 		msr_info->data = vmcs_read64(GUEST_IA32_DEBUGCTL);
 		break;
+	case MSR_VIRTUAL_ENUMERATION:
+		if (!msr_info->host_initiated &&
+		    !(vcpu->arch.arch_capabilities & ARCH_CAP_VIRTUAL_ENUM))
+			return 1;
+		msr_info->data = vmx->msr_virtual_enumeration;
+		break;
 	default:
 	find_uret_msr:
 		msr = vmx_find_uret_msr(vmx, msr_info->index);
@@ -2437,6 +2448,14 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		}
 		ret = kvm_set_msr_common(vcpu, msr_info);
 		break;
+	case MSR_VIRTUAL_ENUMERATION:
+		if (!msr_info->host_initiated)
+			return 1;
+		if (data & ~VIRTUAL_ENUMERATION_VALID_BITS)
+			return 1;
+
+		vmx->msr_virtual_enumeration = data;
+		break;
 
 	default:
 	find_uret_msr:
diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index 021d86b52e18..a7faaf9fdc26 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -292,6 +292,7 @@ struct vcpu_vmx {
 
 	u64		      spec_ctrl;
 	u64		      guest_spec_ctrl;
+	u64		      msr_virtual_enumeration;
 	u32		      msr_ia32_umwait_control;
 
 	/*
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 3c58dbae7b4c..a1bc52bebdcc 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1537,6 +1537,7 @@ static const u32 emulated_msrs_all[] = {
 
 	MSR_K7_HWCR,
 	MSR_KVM_POLL_CONTROL,
+	MSR_VIRTUAL_ENUMERATION,
 };
 
 static u32 emulated_msrs[ARRAY_SIZE(emulated_msrs_all)];
@@ -1570,6 +1571,7 @@ static const u32 msr_based_features_all[] = {
 	MSR_IA32_UCODE_REV,
 	MSR_IA32_ARCH_CAPABILITIES,
 	MSR_IA32_PERF_CAPABILITIES,
+	MSR_VIRTUAL_ENUMERATION,
 };
 
 static u32 msr_based_features[ARRAY_SIZE(msr_based_features_all)];
@@ -1591,7 +1593,8 @@ static unsigned int num_msr_based_features;
 	 ARCH_CAP_SKIP_VMENTRY_L1DFLUSH | ARCH_CAP_SSB_NO | ARCH_CAP_MDS_NO | \
 	 ARCH_CAP_PSCHANGE_MC_NO | ARCH_CAP_TSX_CTRL_MSR | ARCH_CAP_TAA_NO | \
 	 ARCH_CAP_SBDR_SSDP_NO | ARCH_CAP_FBSDP_NO | ARCH_CAP_PSDP_NO | \
-	 ARCH_CAP_FB_CLEAR | ARCH_CAP_RRSBA | ARCH_CAP_PBRSB_NO)
+	 ARCH_CAP_FB_CLEAR | ARCH_CAP_RRSBA | ARCH_CAP_PBRSB_NO | \
+	 ARCH_CAP_VIRTUAL_ENUM)
 
 static u64 kvm_get_arch_capabilities(void)
 {
@@ -1610,6 +1613,17 @@ static u64 kvm_get_arch_capabilities(void)
 	 */
 	data |= ARCH_CAP_PSCHANGE_MC_NO;
 
+	/*
+	 * Virtual enumeration is a paravirt feature. The only usage for now
+	 * is to bridge the gap caused by microarchitecture changes between
+	 * different Intel processors. And its usage is linked to "virtualize
+	 * IA32_SPEC_CTRL" which is a VMX feature. Whether AMD SVM can benefit
+	 * from the same usage and how to implement it is still unclear. Limit
+	 * virtual enumeration to VMX.
+	 */
+	if (static_call(kvm_x86_has_emulated_msr)(NULL, MSR_VIRTUAL_ENUMERATION))
+		data |= ARCH_CAP_VIRTUAL_ENUM;
+
 	/*
 	 * If we're doing cache flushes (either "always" or "cond")
 	 * we will do one whenever the guest does a vmlaunch/vmresume.
-- 
2.40.0