linux-kernel - [PATCH v18 103/121] KVM: TDX: Handle MSR IA32_FEAT_CTL MSR and IA32_MCG_EXT

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Date: Mon, 22 Jan 2024 15:54:19 -0800
From: isaku.yamahata@...el.com
To: kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: isaku.yamahata@...el.com,
	isaku.yamahata@...il.com,
	Paolo Bonzini <pbonzini@...hat.com>,
	erdemaktas@...gle.com,
	Sean Christopherson <seanjc@...gle.com>,
	Sagi Shahar <sagis@...gle.com>,
	Kai Huang <kai.huang@...el.com>,
	chen.bo@...el.com,
	hang.yuan@...el.com,
	tina.zhang@...el.com
Subject: [PATCH v18 103/121] KVM: TDX: Handle MSR IA32_FEAT_CTL MSR and IA32_MCG_EXT_CTL

From: Isaku Yamahata <isaku.yamahata@...el.com>

MCE and MCA is advertised via cpuid based on the TDX module spec.  Guest
kernel can access IA32_FEAT_CTL for checking if LMCE is enabled by platform
and IA32_MCG_EXT_CTL to enable LMCE.  Make TDX KVM handle them.  Otherwise
guest MSR access to them with TDG.VP.VMCALL<MSR> on VE results in GP in
guest.

Because LMCE is disabled with qemu by default, "-cpu lmce=on" to qemu
command line is needed to reproduce it.

Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
---
 arch/x86/kvm/vmx/tdx.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index a75275f6f161..5a2b211a365c 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -1998,6 +1998,7 @@ bool tdx_has_emulated_msr(u32 index, bool write)
 		default:
 			return true;
 		}
+	case MSR_IA32_FEAT_CTL:
 	case MSR_IA32_APICBASE:
 	case MSR_EFER:
 		return !write;
@@ -2012,6 +2013,20 @@ bool tdx_has_emulated_msr(u32 index, bool write)
 int tdx_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
 {
 	switch (msr->index) {
+	case MSR_IA32_FEAT_CTL:
+		/*
+		 * MCE and MCA are advertised via cpuid. guest kernel could
+		 * check if LMCE is enabled or not.
+		 */
+		msr->data = FEAT_CTL_LOCKED;
+		if (vcpu->arch.mcg_cap & MCG_LMCE_P)
+			msr->data |= FEAT_CTL_LMCE_ENABLED;
+		return 0;
+	case MSR_IA32_MCG_EXT_CTL:
+		if (!msr->host_initiated && !(vcpu->arch.mcg_cap & MCG_LMCE_P))
+			return 1;
+		msr->data = vcpu->arch.mcg_ext_ctl;
+		return 0;
 	case MSR_MTRRcap:
 		/*
 		 * Override kvm_mtrr_get_msr() which hardcodes the value.
@@ -2030,6 +2045,11 @@ int tdx_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
 int tdx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
 {
 	switch (msr->index) {
+	case MSR_IA32_MCG_EXT_CTL:
+		if (!msr->host_initiated && !(vcpu->arch.mcg_cap & MCG_LMCE_P))
+			return 1;
+		vcpu->arch.mcg_ext_ctl = msr->data;
+		return 0;
 	case MSR_MTRRdefType:
 		/*
 		 * Allow writeback only for all memory.
-- 
2.25.1