KVM: nVMX: Add support for activity state HLT

We can easily emulate the HLT activity state for L1: If it decides that
L2 shall be halted on entry, just invoke the normal emulation of halt
after switching to L2. We do not depend on specific host features to
provide this, so we can expose the capability unconditionally.
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/include/asm/vmx.h

@@ -100,6 +100,7 @@
 
 #define VMX_MISC_PREEMPTION_TIMER_RATE_MASK	0x0000001f
 #define VMX_MISC_SAVE_EFER_LMA			0x00000020
+#define VMX_MISC_ACTIVITY_HLT			0x00000040
 
 /* VMCS Encodings */
 enum vmcs_field {

arch/x86/kvm/vmx.c

@@ -2340,6 +2340,7 @@ static __init void nested_vmx_setup_ctls_msrs(void)
 	rdmsr(MSR_IA32_VMX_MISC, nested_vmx_misc_low, nested_vmx_misc_high);
 	nested_vmx_misc_low &= VMX_MISC_PREEMPTION_TIMER_RATE_MASK |
 		VMX_MISC_SAVE_EFER_LMA;
+	nested_vmx_misc_low |= VMX_MISC_ACTIVITY_HLT;
 	nested_vmx_misc_high = 0;
 }
 
@@ -7938,7 +7939,8 @@ static int nested_vmx_run(struct kvm_vcpu *vcpu, bool launch)
 		return 1;
 	}
 
-	if (vmcs12->guest_activity_state != GUEST_ACTIVITY_ACTIVE) {
+	if (vmcs12->guest_activity_state != GUEST_ACTIVITY_ACTIVE &&
+	    vmcs12->guest_activity_state != GUEST_ACTIVITY_HLT) {
 		nested_vmx_failValid(vcpu, VMXERR_ENTRY_INVALID_CONTROL_FIELD);
 		return 1;
 	}
@@ -8067,6 +8069,9 @@ static int nested_vmx_run(struct kvm_vcpu *vcpu, bool launch)
 
 	prepare_vmcs02(vcpu, vmcs12);
 
+	if (vmcs12->guest_activity_state == GUEST_ACTIVITY_HLT)
+		return kvm_emulate_halt(vcpu);
+
 	/*
 	 * Note no nested_vmx_succeed or nested_vmx_fail here. At this point
 	 * we are no longer running L1, and VMLAUNCH/VMRESUME has not yet