diff --git a/tools/testing/selftests/kvm/demand_paging_test.c b/tools/testing/selftests/kvm/demand_paging_test.c
index d82f7bc060c3..360cd3ea4cd6 100644
--- a/tools/testing/selftests/kvm/demand_paging_test.c
+++ b/tools/testing/selftests/kvm/demand_paging_test.c
@@ -117,8 +117,7 @@ static void *vcpu_worker(void *data)
 	struct kvm_vm *vm = args->vm;
 	int vcpu_id = args->vcpu_id;
 	struct kvm_run *run;
-	struct timespec start;
-	struct timespec end;
+	struct timespec start, end, ts_diff;
 
 	vcpu_args_set(vm, vcpu_id, 1, vcpu_id);
 	run = vcpu_state(vm, vcpu_id);
@@ -135,9 +134,9 @@ static void *vcpu_worker(void *data)
 	}
 
 	clock_gettime(CLOCK_MONOTONIC, &end);
-	PER_VCPU_DEBUG("vCPU %d execution time: %lld.%.9lds\n", vcpu_id,
-		       (long long)(timespec_diff(start, end).tv_sec),
-		       timespec_diff(start, end).tv_nsec);
+	ts_diff = timespec_sub(end, start);
+	PER_VCPU_DEBUG("vCPU %d execution time: %ld.%.9lds\n", vcpu_id,
+		       ts_diff.tv_sec, ts_diff.tv_nsec);
 
 	return NULL;
 }
@@ -201,8 +200,8 @@ static int handle_uffd_page_request(int uffd, uint64_t addr)
 
 	clock_gettime(CLOCK_MONOTONIC, &end);
 
-	PER_PAGE_DEBUG("UFFDIO_COPY %d \t%lld ns\n", tid,
-		       (long long)timespec_to_ns(timespec_diff(start, end)));
+	PER_PAGE_DEBUG("UFFDIO_COPY %d \t%ld ns\n", tid,
+		       timespec_to_ns(timespec_sub(end, start)));
 	PER_PAGE_DEBUG("Paged in %ld bytes at 0x%lx from thread %d\n",
 		       host_page_size, addr, tid);
 
@@ -224,8 +223,7 @@ static void *uffd_handler_thread_fn(void *arg)
 	int pipefd = uffd_args->pipefd;
 	useconds_t delay = uffd_args->delay;
 	int64_t pages = 0;
-	struct timespec start;
-	struct timespec end;
+	struct timespec start, end, ts_diff;
 
 	clock_gettime(CLOCK_MONOTONIC, &start);
 	while (!quit_uffd_thread) {
@@ -295,11 +293,10 @@ static void *uffd_handler_thread_fn(void *arg)
 	}
 
 	clock_gettime(CLOCK_MONOTONIC, &end);
-	PER_VCPU_DEBUG("userfaulted %ld pages over %lld.%.9lds. (%f/sec)\n",
-		       pages, (long long)(timespec_diff(start, end).tv_sec),
-		       timespec_diff(start, end).tv_nsec, pages /
-		       ((double)timespec_diff(start, end).tv_sec +
-			(double)timespec_diff(start, end).tv_nsec / 100000000.0));
+	ts_diff = timespec_sub(end, start);
+	PER_VCPU_DEBUG("userfaulted %ld pages over %ld.%.9lds. (%f/sec)\n",
+		       pages, ts_diff.tv_sec, ts_diff.tv_nsec,
+		       pages / ((double)ts_diff.tv_sec + (double)ts_diff.tv_nsec / 100000000.0));
 
 	return NULL;
 }
@@ -360,13 +357,12 @@ static void run_test(enum vm_guest_mode mode, bool use_uffd,
 	pthread_t *vcpu_threads;
 	pthread_t *uffd_handler_threads = NULL;
 	struct uffd_handler_args *uffd_args = NULL;
+	struct timespec start, end, ts_diff;
 	int *pipefds = NULL;
 	struct kvm_vm *vm;
 	uint64_t guest_num_pages;
 	int vcpu_id;
 	int r;
-	struct timespec start;
-	struct timespec end;
 
 	vm = create_vm(mode, vcpus, vcpu_memory_bytes);
 
@@ -514,12 +510,11 @@ static void run_test(enum vm_guest_mode mode, bool use_uffd,
 		}
 	}
 
-	pr_info("Total guest execution time: %lld.%.9lds\n",
-		(long long)(timespec_diff(start, end).tv_sec),
-		timespec_diff(start, end).tv_nsec);
+	ts_diff = timespec_sub(end, start);
+	pr_info("Total guest execution time: %ld.%.9lds\n",
+		ts_diff.tv_sec, ts_diff.tv_nsec);
 	pr_info("Overall demand paging rate: %f pgs/sec\n",
-		guest_num_pages / ((double)timespec_diff(start, end).tv_sec +
-		(double)timespec_diff(start, end).tv_nsec / 100000000.0));
+		guest_num_pages / ((double)ts_diff.tv_sec + (double)ts_diff.tv_nsec / 100000000.0));
 
 	ucall_uninit(vm);
 	kvm_vm_free(vm);
diff --git a/tools/testing/selftests/kvm/include/test_util.h b/tools/testing/selftests/kvm/include/test_util.h
index f588ad1403f1..5eb01bf51b86 100644
--- a/tools/testing/selftests/kvm/include/test_util.h
+++ b/tools/testing/selftests/kvm/include/test_util.h
@@ -61,7 +61,8 @@ void test_assert(bool exp, const char *exp_str,
 size_t parse_size(const char *size);
 
 int64_t timespec_to_ns(struct timespec ts);
-struct timespec timespec_diff(struct timespec start, struct timespec end);
 struct timespec timespec_add_ns(struct timespec ts, int64_t ns);
+struct timespec timespec_add(struct timespec ts1, struct timespec ts2);
+struct timespec timespec_sub(struct timespec ts1, struct timespec ts2);
 
 #endif /* SELFTEST_KVM_TEST_UTIL_H */
diff --git a/tools/testing/selftests/kvm/lib/test_util.c b/tools/testing/selftests/kvm/lib/test_util.c
index ee12c4b9ae05..689e97c27ee2 100644
--- a/tools/testing/selftests/kvm/lib/test_util.c
+++ b/tools/testing/selftests/kvm/lib/test_util.c
@@ -56,36 +56,31 @@ int64_t timespec_to_ns(struct timespec ts)
 	return (int64_t)ts.tv_nsec + 1000000000LL * (int64_t)ts.tv_sec;
 }
 
-struct timespec timespec_diff(struct timespec start, struct timespec end)
-{
-	struct timespec temp;
-
-	if ((end.tv_nsec - start.tv_nsec) < 0) {
-		temp.tv_sec = end.tv_sec - start.tv_sec - 1;
-		temp.tv_nsec = 1000000000LL + end.tv_nsec - start.tv_nsec;
-	} else {
-		temp.tv_sec = end.tv_sec - start.tv_sec;
-		temp.tv_nsec = end.tv_nsec - start.tv_nsec;
-	}
-
-	return temp;
-}
-
 struct timespec timespec_add_ns(struct timespec ts, int64_t ns)
 {
 	struct timespec res;
 
-	res.tv_sec = ts.tv_sec;
 	res.tv_nsec = ts.tv_nsec + ns;
-
-	if (res.tv_nsec > 1000000000UL) {
-		res.tv_sec += 1;
-		res.tv_nsec -= 1000000000UL;
-	}
+	res.tv_sec = ts.tv_sec + res.tv_nsec / 1000000000LL;
+	res.tv_nsec %= 1000000000LL;
 
 	return res;
 }
 
+struct timespec timespec_add(struct timespec ts1, struct timespec ts2)
+{
+	int64_t ns1 = timespec_to_ns(ts1);
+	int64_t ns2 = timespec_to_ns(ts2);
+	return timespec_add_ns((struct timespec){0}, ns1 + ns2);
+}
+
+struct timespec timespec_sub(struct timespec ts1, struct timespec ts2)
+{
+	int64_t ns1 = timespec_to_ns(ts1);
+	int64_t ns2 = timespec_to_ns(ts2);
+	return timespec_add_ns((struct timespec){0}, ns1 - ns2);
+}
+
 void print_skip(const char *fmt, ...)
 {
 	va_list ap;
diff --git a/tools/testing/selftests/kvm/steal_time.c b/tools/testing/selftests/kvm/steal_time.c
index 21990d653099..86f30eda0ae7 100644
--- a/tools/testing/selftests/kvm/steal_time.c
+++ b/tools/testing/selftests/kvm/steal_time.c
@@ -242,7 +242,7 @@ static void *do_steal_time(void *arg)
 
 	while (1) {
 		clock_gettime(CLOCK_MONOTONIC, &ts);
-		if (ts.tv_sec > stop.tv_sec || ts.tv_nsec >= stop.tv_nsec)
+		if (timespec_to_ns(timespec_sub(ts, stop)) >= 0)
 			break;
 	}
 
