[PATCH kvmtool v3 2/3] cpu: vmexit: Retry KVM_RUN ioctl on EINTR and EAGAIN

["Aneesh Kumar K.V (Arm)" <aneesh.kumar@kernel.org>]

When KVM_RUN fails with EINTR or EAGAIN, we should retry the ioctl
without checking kvm_run->exit_reason. These errors don't indicate a
valid VM exit, hence exit_reason may contain stale or undefined values.

Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel.org>
---
 include/kvm/kvm-cpu.h |  2 +-
 kvm-cpu.c             | 17 ++++++++++++-----
 2 files changed, 13 insertions(+), 6 deletions(-)

diff --git a/include/kvm/kvm-cpu.h b/include/kvm/kvm-cpu.h
index 8f76f8a1123a..72cbb86e6cef 100644
--- a/include/kvm/kvm-cpu.h
+++ b/include/kvm/kvm-cpu.h
@@ -16,7 +16,7 @@ void kvm_cpu__delete(struct kvm_cpu *vcpu);
 void kvm_cpu__reset_vcpu(struct kvm_cpu *vcpu);
 void kvm_cpu__setup_cpuid(struct kvm_cpu *vcpu);
 void kvm_cpu__enable_singlestep(struct kvm_cpu *vcpu);
-void kvm_cpu__run(struct kvm_cpu *vcpu);
+int kvm_cpu__run(struct kvm_cpu *vcpu);
 int kvm_cpu__start(struct kvm_cpu *cpu);
 bool kvm_cpu__handle_exit(struct kvm_cpu *vcpu);
 int kvm_cpu__get_endianness(struct kvm_cpu *vcpu);
diff --git a/kvm-cpu.c b/kvm-cpu.c
index 40041a22b3fe..7abbdcebf075 100644
--- a/kvm-cpu.c
+++ b/kvm-cpu.c
@@ -35,27 +35,32 @@ void kvm_cpu__enable_singlestep(struct kvm_cpu *vcpu)
 		pr_warning("KVM_SET_GUEST_DEBUG failed");
 }
 
-void kvm_cpu__run(struct kvm_cpu *vcpu)
+/*
+ * return value -1 if we need to call the kvm_cpu__run again without checking
+ * exit_reason. return value 0 results in taking action based on exit_reason.
+ */
+int kvm_cpu__run(struct kvm_cpu *vcpu)
 {
 	int err;
 
 	if (!vcpu->is_running)
-		return;
+		return -1;
 
 	err = ioctl(vcpu->vcpu_fd, KVM_RUN, 0);
 	if (err < 0) {
 		switch (errno) {
 		case EINTR:
 		case EAGAIN:
-			return;
+			return -1;
 		case EFAULT:
 			if (vcpu->kvm_run->exit_reason == KVM_EXIT_MEMORY_FAULT)
-				return;
+				return 0;
 			/* fallthrough */
 		default:
 			die_perror("KVM_RUN failed");
 		}
 	}
+	return 0;
 }
 
 static void kvm_cpu_signal_handler(int signum)
@@ -179,7 +184,9 @@ int kvm_cpu__start(struct kvm_cpu *cpu)
 		if (cpu->task)
 			kvm_cpu__run_task(cpu);
 
-		kvm_cpu__run(cpu);
+		if (kvm_cpu__run(cpu) == -1)
+			/* retry without an exit_reason check */
+			continue;
 
 		switch (cpu->kvm_run->exit_reason) {
 		case KVM_EXIT_UNKNOWN:
-- 
2.43.0