kvm tools: Exit VCPU thread only when SIGKVMEXIT is received

Currently the VCPU loop would exit when the thread received any signal.

Change behaviour to exit only when SIGKVMEXIT is received. This change
prevents from the guest to terminate when unrelated signals are processed
by the thread (for example, when attaching a debugger).

Signed-off-by: Sasha Levin <levinsasha928@gmail.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>

include/kvm/kvm-cpu.h

@@ -21,6 +21,8 @@ struct kvm_cpu {
 	struct kvm_fpu		fpu;
 
 	struct kvm_msrs		*msrs;		/* dynamically allocated */
+
+	u8			is_running;
 };
 
 struct kvm_cpu *kvm_cpu__init(struct kvm *kvm, unsigned long cpu_id);

kvm-cpu.c

@@ -14,6 +14,8 @@
 #include <errno.h>
 #include <stdio.h>
 
+extern __thread struct kvm_cpu *current_kvm_cpu;
+
 static inline bool is_in_protected_mode(struct kvm_cpu *vcpu)
 {
 	return vcpu->sregs.cr0 & 0x01;
@@ -87,6 +89,8 @@ struct kvm_cpu *kvm_cpu__init(struct kvm *kvm, unsigned long cpu_id)
 	if (vcpu->kvm_run == MAP_FAILED)
 		die("unable to mmap vcpu fd");
 
+	vcpu->is_running = true;
+
 	return vcpu;
 }
 
@@ -381,7 +385,10 @@ void kvm_cpu__run(struct kvm_cpu *vcpu)
 
 static void kvm_cpu_exit_handler(int signum)
 {
-	/* Don't do anything here */
+	if (current_kvm_cpu->is_running) {
+		current_kvm_cpu->is_running = false;
+		pthread_kill(pthread_self(), SIGKVMEXIT);
+	}
 }
 
 int kvm_cpu__start(struct kvm_cpu *cpu)
@@ -437,10 +444,8 @@ int kvm_cpu__start(struct kvm_cpu *cpu)
 			break;
 		}
 		case KVM_EXIT_INTR:
-			/*
-			 * Currently we only handle exit signal, which means
-			 * we just exit if KVM_RUN exited due to a signal.
-			 */
+			if (cpu->is_running)
+				break;
 			goto exit_kvm;
 		case KVM_EXIT_SHUTDOWN:
 			goto exit_kvm;

kvm-run.c

@@ -48,7 +48,7 @@
 
 static struct kvm *kvm;
 static struct kvm_cpu *kvm_cpus[KVM_NR_CPUS];
-static __thread struct kvm_cpu *current_kvm_cpu;
+__thread struct kvm_cpu *current_kvm_cpu;
 
 static u64 ram_size;
 static u8  image_count;