[RFC PATCH 6/9] kvm/x86: Add ARCH_CAP_VIRTUAL_ENUM for guest MSR_IA32_ARCH_CAPABILITIES

[Zhang Chen]

Add the 63 bit in MSR_IA32_ARCH_CAPABILITIES for enable the virtual MSRs.
Virtual MSRs can allow guests to notify VMM whether or not
they are using specific software mitigation, allowing a VMM
to enable there hardware control only where necessary.
As Intel spec defination, expose virtual MSR for guest.
Make guest have ability to check virtual MSR 0x50000000.

Signed-off-by: Zhang Chen <chen.zhang@xxxxxxxxx>
---
 arch/x86/kvm/vmx/vmx.c | 15 +++++++++++++++
 arch/x86/kvm/vmx/vmx.h |  1 +
 arch/x86/kvm/x86.c     | 16 +++++++++++++++-
 3 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 407061b369b4..6ed6b743be0e 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -2001,6 +2001,12 @@ 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);
@@ -2375,6 +2381,15 @@ 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 &&
+		    !(vcpu->arch.arch_capabilities & ARCH_CAP_VIRTUAL_ENUM))
+			return 1;
+		if (data & ~VIRT_ENUM_MITIGATION_CTRL_SUPPORT)
+			return 1;
+		vmx->msr_virtual_enumeration = data &
+						VIRT_ENUM_MITIGATION_CTRL_SUPPORT;
+		break;
 
 	default:
 	find_uret_msr:
diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index c5a41ae14237..fc873cf45f70 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -298,6 +298,7 @@ struct vcpu_vmx {
 	 * IA32_SPEC_CTRL_MSR.
 	 */
 	u64		      spec_ctrl_mask;
+	u64		      msr_virtual_enumeration;
 	u32		      msr_ia32_umwait_control;
 
 	/*
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 2835bd796639..6be0a3f1281f 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1532,6 +1532,8 @@ static const u32 emulated_msrs_all[] = {
 	MSR_IA32_VMX_EPT_VPID_CAP,
 	MSR_IA32_VMX_VMFUNC,
 
+	MSR_VIRTUAL_ENUMERATION,
+
 	MSR_K7_HWCR,
 	MSR_KVM_POLL_CONTROL,
 };
@@ -1567,6 +1569,7 @@ 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)];
@@ -1588,7 +1591,8 @@ 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)
 {
@@ -1607,6 +1611,13 @@ static u64 kvm_get_arch_capabilities(void)
 	 */
 	data |= ARCH_CAP_PSCHANGE_MC_NO;
 
+	/*
+	 * Virtual MSRs can allow guests to notify VMM whether or not
+	 * they are using specific software mitigation, allowing a VMM
+	 * to enable there hardware control only where necessary.
+	 */
+	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.
@@ -1657,6 +1668,9 @@ static int kvm_get_msr_feature(struct kvm_msr_entry *msr)
 	case MSR_IA32_UCODE_REV:
 		rdmsrl_safe(msr->index, &msr->data);
 		break;
+	case MSR_VIRTUAL_ENUMERATION:
+		msr->data = VIRT_ENUM_MITIGATION_CTRL_SUPPORT;
+		break;
 	default:
 		return static_call(kvm_x86_get_msr_feature)(msr);
 	}
-- 
2.25.1