Allow userspace to set all supported bits in MSR IA32_FEATURE_CONTROL
irrespective of the guest CPUID model, e.g. via KVM_SET_MSRS. KVM's ABI
is that userspace is allowed to set MSRs before CPUID, i.e. can set MSRs
to values that would fault according to the guest CPUID model.
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
arch/x86/kvm/vmx/vmx.c | 36 +++++++++++++++++++++++++++++++-----
1 file changed, 31 insertions(+), 5 deletions(-)
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index fd2e707faf2b..8e83e12373c5 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -1741,12 +1741,38 @@ bool nested_vmx_allowed(struct kvm_vcpu *vcpu)
return nested && guest_cpuid_has(vcpu, X86_FEATURE_VMX);
}
-static inline bool vmx_feature_control_msr_valid(struct kvm_vcpu *vcpu,
- uint64_t val)
+/*
+ * Userspace is allowed to set any supported IA32_FEATURE_CONTROL regardless of
+ * guest CPUID. Note, KVM allows userspace to set "VMX in SMX" to maintain
+ * backwards compatibility even though KVM doesn't support emulating SMX. And
+ * because userspace set "VMX in SMX", the guest must also be allowed to set it,
+ * e.g. if the MSR is left unlocked and the guest does a RMW operation.
+ */
+#define KVM_SUPPORTED_FEATURE_CONTROL (FEAT_CTL_LOCKED | \
+ FEAT_CTL_VMX_ENABLED_INSIDE_SMX | \
+ FEAT_CTL_VMX_ENABLED_OUTSIDE_SMX | \
+ FEAT_CTL_SGX_LC_ENABLED | \
+ FEAT_CTL_SGX_ENABLED | \
+ FEAT_CTL_LMCE_ENABLED)
+
+static inline bool vmx_feature_control_msr_valid(struct vcpu_vmx *vmx,
+ struct msr_data *msr)
{
- uint64_t valid_bits = to_vmx(vcpu)->msr_ia32_feature_control_valid_bits;
+ uint64_t valid_bits;
- return !(val & ~valid_bits);
+ /*
+ * Ensure KVM_SUPPORTED_FEATURE_CONTROL is updated when new bits are
+ * exposed to the guest.
+ */
+ WARN_ON_ONCE(vmx->msr_ia32_feature_control_valid_bits &
+ ~KVM_SUPPORTED_FEATURE_CONTROL);
+
+ if (msr->host_initiated)
+ valid_bits = KVM_SUPPORTED_FEATURE_CONTROL;
+ else
+ valid_bits = vmx->msr_ia32_feature_control_valid_bits;
+
+ return !(msr->data & ~valid_bits);
}
static int vmx_get_msr_feature(struct kvm_msr_entry *msr)
@@ -2139,7 +2165,7 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
vcpu->arch.mcg_ext_ctl = data;
break;
case MSR_IA32_FEAT_CTL:
- if (!vmx_feature_control_msr_valid(vcpu, data) ||
+ if (!vmx_feature_control_msr_valid(vmx, msr_info) ||
(to_vmx(vcpu)->msr_ia32_feature_control &
FEAT_CTL_LOCKED && !msr_info->host_initiated))
return 1;
--
2.36.1.255.ge46751e96f-goog
