KVM: VMX: Set EDX at INIT with CPUID.0x1, Family-Model-Stepping

Set EDX at RESET/INIT based on the userspace-defined CPUID model when
possible, i.e. when CPUID.0x1.EAX is defind by userspace.  At RESET/INIT,
all CPUs that support CPUID set EDX to the FMS enumerated in
CPUID.0x1.EAX.  If no CPUID match is found, fall back to KVM's default
of 0x600 (Family '6'), which is the least awful approximation of KVM's
virtual CPU model.

Fixes: 6aa8b732 ("[PATCH] kvm: userspace interface")
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210713163324.627647-5-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx/vmx.c

@@ -4394,6 +4394,7 @@ static void vmx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
 	struct msr_data apic_base_msr;
+	u32 eax, dummy;
 	u64 cr0;
 
 	vmx->rmode.vm86_active = 0;
@@ -4401,7 +4402,11 @@ static void vmx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
 
 	vmx->msr_ia32_umwait_control = 0;
 
-	vmx->vcpu.arch.regs[VCPU_REGS_RDX] = get_rdx_init_val();
+	eax = 1;
+	if (!kvm_cpuid(vcpu, &eax, &dummy, &dummy, &dummy, true))
+		eax = get_rdx_init_val();
+	kvm_rdx_write(vcpu, eax);
+
 	vmx->hv_deadline_tsc = -1;
 	kvm_set_cr8(vcpu, 0);