KVM: Add guest mode signal mask

Allow a special signal mask to be used while executing in guest mode.  This
allows signals to be used to interrupt a vcpu without requiring signal
delivery to a userspace handler, which is quite expensive.  Userspace still
receives -EINTR and can get the signal via sigwait().

Signed-off-by: Avi Kivity <avi@qumranet.com>
diff --git a/drivers/kvm/kvm.h b/drivers/kvm/kvm.h
index be3a0e7..1c4a581 100644
--- a/drivers/kvm/kvm.h
+++ b/drivers/kvm/kvm.h
@@ -277,6 +277,9 @@
 	gpa_t mmio_phys_addr;
 	int pio_pending;
 
+	int sigset_active;
+	sigset_t sigset;
+
 	struct {
 		int active;
 		u8 save_iopl;