KVM: nVMX: Enable unrestricted guest mode support

Now that we provide EPT support, there is no reason to torture our
guests by hiding the relieving unrestricted guest mode feature. We just
need to relax CR0 checks for always-on bits as PE and PG can now be
switched off.

Signed-off-by: Jan Kiszka <[e-mail]>
Reviewed-by: Gleb Natapov <[e-mail]>
Signed-off-by: Paolo Bonzini <[e-mail]>

arch/x86/kvm/vmx.c

···
 	nested_vmx_secondary_ctls_low = 0;
 	nested_vmx_secondary_ctls_high &=
 		SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES |
+		SECONDARY_EXEC_UNRESTRICTED_GUEST |
 		SECONDARY_EXEC_WBINVD_EXITING;
 
 	if (enable_ept) {
···
 	hypercall[2] = 0xc1;
 }
 
+static bool nested_cr0_valid(struct vmcs12 *vmcs12, unsigned long val)
+{
+	unsigned long always_on = VMXON_CR0_ALWAYSON;
+
+	if (nested_vmx_secondary_ctls_high &
+		SECONDARY_EXEC_UNRESTRICTED_GUEST &&
+	    nested_cpu_has2(vmcs12, SECONDARY_EXEC_UNRESTRICTED_GUEST))
+		always_on &= ~(X86_CR0_PE | X86_CR0_PG);
+	return (val & always_on) == always_on;
+}
+
 /* called to set cr0 as appropriate for a mov-to-cr0 exit. */
 static int handle_set_cr0(struct kvm_vcpu *vcpu, unsigned long val)
 {
···
 		val = (val & ~vmcs12->cr0_guest_host_mask) |
 			(vmcs12->guest_cr0 & vmcs12->cr0_guest_host_mask);
 
-		/* TODO: will have to take unrestricted guest mode into
-		 * account */
-		if ((val & VMXON_CR0_ALWAYSON) != VMXON_CR0_ALWAYSON)
+		if (!nested_cr0_valid(vmcs12, val))
 			return 1;
 
 		if (kvm_set_cr0(vcpu, val))
···
 		return 1;
 	}
 
-	if (((vmcs12->guest_cr0 & VMXON_CR0_ALWAYSON) != VMXON_CR0_ALWAYSON) ||
+	if (!nested_cr0_valid(vmcs12, vmcs12->guest_cr0) ||
 	    ((vmcs12->guest_cr4 & VMXON_CR4_ALWAYSON) != VMXON_CR4_ALWAYSON)) {
 		nested_vmx_entry_failure(vcpu, vmcs12,
 			EXIT_REASON_INVALID_STATE, ENTRY_FAIL_DEFAULT);