KVM: nVMX: Clean up and fix pin-based execution controls

Only interrupt and NMI exiting are mandatory for KVM to work, thus can
be exposed to the guest unconditionally, virtual NMI exiting is
optional. So we must not advertise it unless the host supports it.

Introduce the symbolic constant PIN_BASED_ALWAYSON_WITHOUT_TRUE_MSR at
this chance.

Reviewed-by:: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index af1ffaf..8eaabfb 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -2040,14 +2040,16 @@
 	 */
 
 	/* pin-based controls */
+	rdmsr(MSR_IA32_VMX_PINBASED_CTLS,
+	      nested_vmx_pinbased_ctls_low, nested_vmx_pinbased_ctls_high);
 	/*
 	 * According to the Intel spec, if bit 55 of VMX_BASIC is off (as it is
 	 * in our case), bits 1, 2 and 4 (i.e., 0x16) must be 1 in this MSR.
 	 */
-	nested_vmx_pinbased_ctls_low = 0x16 ;
-	nested_vmx_pinbased_ctls_high = 0x16 |
-		PIN_BASED_EXT_INTR_MASK | PIN_BASED_NMI_EXITING |
-		PIN_BASED_VIRTUAL_NMIS;
+	nested_vmx_pinbased_ctls_low |= PIN_BASED_ALWAYSON_WITHOUT_TRUE_MSR;
+	nested_vmx_pinbased_ctls_high &= PIN_BASED_EXT_INTR_MASK |
+		PIN_BASED_NMI_EXITING | PIN_BASED_VIRTUAL_NMIS;
+	nested_vmx_pinbased_ctls_high |= PIN_BASED_ALWAYSON_WITHOUT_TRUE_MSR;
 
 	/*
 	 * Exit controls