KVM: nSVM: implement KVM_GET_NESTED_STATE and KVM_SET_NESTED_STATE

Similar to VMX, the state that is captured through the currently available
IOCTLs is a mix of L1 and L2 state, dependent on whether the L2 guest was
running at the moment when the process was interrupted to save its state.

In particular, the SVM-specific state for nested virtualization includes
the L1 saved state (including the interrupt flag), the cached L2 controls,
and the GIF.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/x86.c

@@ -4628,7 +4628,8 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
 
 		if (kvm_state.flags &
 		    ~(KVM_STATE_NESTED_RUN_PENDING | KVM_STATE_NESTED_GUEST_MODE
-		      | KVM_STATE_NESTED_EVMCS | KVM_STATE_NESTED_MTF_PENDING))
+		      | KVM_STATE_NESTED_EVMCS | KVM_STATE_NESTED_MTF_PENDING
+		      | KVM_STATE_NESTED_GIF_SET))
 			break;
 
 		/* nested_run_pending implies guest_mode.  */