KVM: TDX: Enable guest access to LMCE related MSRs

Allow TDX guest to configure LMCE (Local Machine Check Event) by handling
MSR IA32_FEAT_CTL and IA32_MCG_EXT_CTL.

MCE and MCA are advertised via cpuid based on the TDX module spec.  Guest
kernel can access IA32_FEAT_CTL to check whether LMCE is opted-in by the
platform or not.  If LMCE is opted-in by the platform, guest kernel can
access IA32_MCG_EXT_CTL to enable/disable LMCE.

Handle MSR IA32_FEAT_CTL and IA32_MCG_EXT_CTL for TDX guests to avoid
failure when a guest accesses them with TDG.VP.VMCALL<MSR> on #VE.  E.g.,
Linux guest will treat the failure as a #GP(0).

Userspace VMM may not opt-in LMCE by default, e.g., QEMU disables it by
default, "-cpu lmce=on" is needed in QEMU command line to opt-in it.

Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
[binbin: rework changelog]
Signed-off-by: Binbin Wu <binbin.wu@linux.intel.com>
Message-ID: <20250227012021.1778144-11-binbin.wu@linux.intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index 6ce2008..1aecb40 100644 (file)
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -2065,6 +2065,7 @@ bool tdx_has_emulated_msr(u32 index)
        case MSR_MISC_FEATURES_ENABLES:
        case MSR_IA32_APICBASE:
        case MSR_EFER:
+       case MSR_IA32_FEAT_CTL:
        case MSR_IA32_MCG_CAP:
        case MSR_IA32_MCG_STATUS:
        case MSR_IA32_MCG_CTL:
@@ -2097,26 +2098,53 @@ bool tdx_has_emulated_msr(u32 index)
 
 static bool tdx_is_read_only_msr(u32 index)
 {
-       return  index == MSR_IA32_APICBASE || index == MSR_EFER;
+       return  index == MSR_IA32_APICBASE || index == MSR_EFER ||
+               index == MSR_IA32_FEAT_CTL;
 }
 
 int tdx_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
 {
-       if (!tdx_has_emulated_msr(msr->index))
-               return 1;
+       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;
+       default:
+               if (!tdx_has_emulated_msr(msr->index))
+                       return 1;
 
-       return kvm_get_msr_common(vcpu, msr);
+               return kvm_get_msr_common(vcpu, msr);
+       }
 }
 
 int tdx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
 {
-       if (tdx_is_read_only_msr(msr->index))
-               return 1;
+       switch (msr->index) {
+       case MSR_IA32_MCG_EXT_CTL:
+               if ((!msr->host_initiated && !(vcpu->arch.mcg_cap & MCG_LMCE_P)) ||
+                   (msr->data & ~MCG_EXT_CTL_LMCE_EN))
+                       return 1;
+               vcpu->arch.mcg_ext_ctl = msr->data;
+               return 0;
+       default:
+               if (tdx_is_read_only_msr(msr->index))
+                       return 1;
 
-       if (!tdx_has_emulated_msr(msr->index))
-               return 1;
+               if (!tdx_has_emulated_msr(msr->index))
+                       return 1;
 
-       return kvm_set_msr_common(vcpu, msr);
+               return kvm_set_msr_common(vcpu, msr);
+       }
 }
 
 static int tdx_get_capabilities(struct kvm_tdx_cmd *cmd)