[PATCH 6/8] KVM: selftests: Trigger save+restore randomly in the #PF stress test

[Yosry Ahmed]

From: Yosry Ahmed <yosryahmed@xxxxxxxxxx>

Instead of an explicit GUEST_SYNC() after each access+#PF, run another
thread that keeps sending SIGUSR to the vCPU thread, essentially
triggering exits to userspace and save+restore on random points in guest
execution. This makes the test a lot more meaningful as it opens the
door to exercising race conditions between #PF handling in the guest
and save+restore in the host.

The signals are ignored using SIG_IGN outside of __vcpu_run() to avoid
interrupting other ioctls/sysctls performed by the test.

Signed-off-by: Yosry Ahmed <yosry@xxxxxxxxxx>
---
 .../kvm/x86/stress_save_restore_pf_test.c     | 56 ++++++++++++++++---
 1 file changed, 48 insertions(+), 8 deletions(-)

diff --git a/tools/testing/selftests/kvm/x86/stress_save_restore_pf_test.c b/tools/testing/selftests/kvm/x86/stress_save_restore_pf_test.c
index 12da74b4f725c..60a013e0f14fb 100644
--- a/tools/testing/selftests/kvm/x86/stress_save_restore_pf_test.c
+++ b/tools/testing/selftests/kvm/x86/stress_save_restore_pf_test.c
@@ -5,6 +5,8 @@
 #include <errno.h>
 #include <sys/types.h>
 #include <time.h>
+#include <pthread.h>
+#include <signal.h>
 #include <unistd.h>
 
 #include "test_util.h"
@@ -99,14 +101,40 @@ static void guest_access_memory(void *arg)
 		/* Clear the present bit again so it faults next time */
 		*guest_get_pte(vaddr) &= ~pte_present_mask;
 		invlpg(vaddr);
+	}
+}
+
+static void *sigusr_thread_fn(void *arg)
+{
+	pthread_t vcpu_thread = (pthread_t)arg;
 
-		GUEST_SYNC(guest_accesses);
+	for (;;) {
+		pthread_testcancel();
+		pthread_kill(vcpu_thread, SIGUSR1);
+		usleep(100);
 	}
+	return NULL;
+}
+
+static void dummy_signal_handler(int signo) {}
+static struct sigaction sa;
+
+static void vcpu_sigusr_listen(void)
+{
+	sa.sa_handler = dummy_signal_handler;
+	sigaction(SIGUSR1, &sa, NULL);
+}
+
+static void vcpu_sigusr_ignore(void)
+{
+	sa.sa_handler = SIG_IGN;
+	sigaction(SIGUSR1, &sa, NULL);
 }
 
 int main(int argc, char *argv[])
 {
 	struct kvm_x86_state *state;
+	pthread_t sigusr_thread;
 	struct kvm_vcpu *vcpu;
 	int r, i, count = 0;
 	struct kvm_vm *vm;
@@ -140,18 +168,28 @@ int main(int argc, char *argv[])
 	/* Map the page tables so that the guest #PF handler can walk them */
 	virt_map_page_tables(vm);
 
+	/* Initialize the thread sending SIGUSR and install the handler */
+	pthread_create(&sigusr_thread, NULL, sigusr_thread_fn,
+		       (void *)pthread_self());
+
 	while (count++ < NR_ITERATIONS) {
+		/*
+		 * Only handle SIGUSR while the vCPU is running, otherwise
+		 * ignore it to avoid interrupting other ioctls/syscalls.
+		 */
+		vcpu_sigusr_listen();
 		r = __vcpu_run(vcpu);
-		TEST_ASSERT(!r, "vcpu_run failed");
-		TEST_ASSERT_KVM_EXIT_REASON(vcpu, KVM_EXIT_IO);
-
-		get_ucall(vcpu, &uc);
-		if (uc.cmd == UCALL_ABORT) {
+		if (r == -1)
+			TEST_ASSERT_EQ(errno, EINTR);
+		vcpu_sigusr_ignore();
+
+		/* The guest only exists due to a signal or failed assertion */
+		if (!r) {
+			TEST_ASSERT_KVM_EXIT_REASON(vcpu, KVM_EXIT_IO);
+			TEST_ASSERT_EQ(get_ucall(vcpu, &uc), UCALL_ABORT);
 			REPORT_GUEST_ASSERT(uc);
 			break;
 		}
-		TEST_ASSERT_EQ(uc.cmd, UCALL_SYNC);
-		TEST_ASSERT_EQ(uc.args[1], count - 1);
 
 		state = vcpu_save_state(vcpu);
 
@@ -166,6 +204,8 @@ int main(int argc, char *argv[])
 	sync_global_from_guest(vm, guest_accesses);
 	pr_info("Guest page accesses: %lu\n", guest_accesses);
 
+	pthread_cancel(sigusr_thread);
+	pthread_join(sigusr_thread, NULL);
 	kvm_vm_free(vm);
 	return 0;
 }
-- 
2.54.0.563.g4f69b47b94-goog