[PATCH RFC 15/15] KVM: selftests: Test dirty ring waitqueue

[Peter Xu <peterx@redhat.com>]

This is a bit tricky, but should still be reasonable.

Firstly we introduce a totally new dirty log test type, because we
need to force vcpu to go into a blocked state by dead loop on vcpu_run
even if it wants to quit to userspace.

Here the tricky part is we need to read the procfs to make sure the
vcpu thread is TASK_UNINTERRUPTIBLE.

After that, we reset the ring and the reset should kick the vcpu again
by moving out of that state.

Signed-off-by: Peter Xu <peterx@redhat.com>
---
 tools/testing/selftests/kvm/dirty_log_test.c | 101 +++++++++++++++++++
 1 file changed, 101 insertions(+)

diff --git a/tools/testing/selftests/kvm/dirty_log_test.c b/tools/testing/selftests/kvm/dirty_log_test.c
index c9db136a1f12..41bc015131e1 100644
--- a/tools/testing/selftests/kvm/dirty_log_test.c
+++ b/tools/testing/selftests/kvm/dirty_log_test.c
@@ -16,6 +16,7 @@
 #include <sys/types.h>
 #include <signal.h>
 #include <errno.h>
+#include <sys/syscall.h>
 #include <linux/bitmap.h>
 #include <linux/bitops.h>
 #include <asm/barrier.h>
@@ -151,12 +152,16 @@ enum log_mode_t {
 	/* Use dirty ring for logging */
 	LOG_MODE_DIRTY_RING = 2,
 
+	/* Dirty ring test but tailored for the waitqueue */
+	LOG_MODE_DIRTY_RING_WP = 3,
+
 	LOG_MODE_NUM,
 };
 
 /* Mode of logging.  Default is LOG_MODE_DIRTY_LOG */
 static enum log_mode_t host_log_mode;
 pthread_t vcpu_thread;
+pid_t vcpu_thread_tid;
 static uint32_t test_dirty_ring_count = TEST_DIRTY_RING_COUNT;
 
 /* Only way to pass this to the signal handler */
@@ -221,6 +226,18 @@ static void dirty_ring_create_vm_done(struct kvm_vm *vm)
 			     sizeof(struct kvm_dirty_gfn));
 }
 
+static void dirty_ring_wq_create_vm_done(struct kvm_vm *vm)
+{
+	/*
+	 * Force to use a relatively small ring size, so easier to get
+	 * full.  Better bigger than PML size, hence 1024.
+	 */
+	test_dirty_ring_count = 1024;
+	DEBUG("Forcing ring size: %u\n", test_dirty_ring_count);
+	vm_enable_dirty_ring(vm, test_dirty_ring_count *
+			     sizeof(struct kvm_dirty_gfn));
+}
+
 static uint32_t dirty_ring_collect_one(struct kvm_dirty_gfn *dirty_gfns,
 				       struct kvm_dirty_ring_indexes *indexes,
 				       int slot, void *bitmap,
@@ -295,6 +312,81 @@ static void dirty_ring_collect_dirty_pages(struct kvm_vm *vm, int slot,
 	DEBUG("Iteration %ld collected %u pages\n", iteration, count);
 }
 
+/*
+ * Return 'D' for uninterruptible, 'R' for running, 'S' for
+ * interruptible, etc.
+ */
+static char read_tid_status_char(unsigned int tid)
+{
+	int fd, ret, line = 0;
+	char buf[128], *c;
+
+	snprintf(buf, sizeof(buf) - 1, "/proc/%u/status", tid);
+	fd = open(buf, O_RDONLY);
+	TEST_ASSERT(fd >= 0, "open status file failed: %s", buf);
+	ret = read(fd, buf, sizeof(buf) - 1);
+	TEST_ASSERT(ret > 0, "read status file failed: %d, %d", ret, errno);
+	close(fd);
+
+	/* Skip 2 lines */
+	for (c = buf; c < buf + sizeof(buf) && line < 2; c++) {
+		if (*c == '\n') {
+			line++;
+			continue;
+		}
+	}
+
+	/* Skip "Status:  " */
+	while (*c != ':') c++;
+	c++;
+	while (*c == ' ') c++;
+	c++;
+
+	return *c;
+}
+
+static void dirty_ring_wq_collect_dirty_pages(struct kvm_vm *vm, int slot,
+					      void *bitmap, uint32_t num_pages)
+{
+	uint32_t count = test_dirty_ring_count;
+	struct kvm_run *state = vcpu_state(vm, VCPU_ID);
+	struct kvm_dirty_ring_indexes *indexes = &state->vcpu_ring_indexes;
+	uint32_t avail;
+
+	while (count--) {
+		/*
+		 * Force vcpu to run enough time to make sure we
+		 * trigger the ring full case
+		 */
+		sem_post(&dirty_ring_vcpu_cont);
+	}
+
+	/* Make sure it's stuck */
+	TEST_ASSERT(vcpu_thread_tid, "TID not inited");
+        /*
+	 * Wait for /proc/pid/status "Status:" changes to "D". "D"
+	 * stands for "D (disk sleep)", TASK_UNINTERRUPTIBLE
+	 */
+	while (read_tid_status_char(vcpu_thread_tid) != 'D') {
+		usleep(1000);
+	}
+	DEBUG("Now VCPU thread dirty ring full\n");
+
+	avail = READ_ONCE(indexes->avail_index);
+	/* Assuming we've consumed all */
+	WRITE_ONCE(indexes->fetch_index, avail);
+
+	kvm_vm_reset_dirty_ring(vm);
+
+	/* Wait for it to be awake */
+	while (read_tid_status_char(vcpu_thread_tid) == 'D') {
+		usleep(1000);
+	}
+	DEBUG("VCPU Thread is successfully waked up\n");
+
+	exit(0);
+}
+
 static void dirty_ring_after_vcpu_run(struct kvm_vm *vm, int ret, int err)
 {
 	struct kvm_run *run = vcpu_state(vm, VCPU_ID);
@@ -353,6 +445,12 @@ struct log_mode {
 		.before_vcpu_join = dirty_ring_before_vcpu_join,
 		.after_vcpu_run = dirty_ring_after_vcpu_run,
 	},
+	{
+		.name = "dirty-ring-wait-queue",
+		.create_vm_done = dirty_ring_wq_create_vm_done,
+		.collect_dirty_pages = dirty_ring_wq_collect_dirty_pages,
+		.after_vcpu_run = dirty_ring_after_vcpu_run,
+	},
 };
 
 /*
@@ -422,6 +520,9 @@ static void *vcpu_worker(void *data)
 	uint64_t *guest_array;
 	struct sigaction sigact;
 
+	vcpu_thread_tid = syscall(SYS_gettid);
+	printf("VCPU Thread ID: %u\n", vcpu_thread_tid);
+
 	current_vm = vm;
 	memset(&sigact, 0, sizeof(sigact));
 	sigact.sa_handler = vcpu_sig_handler;
-- 
2.21.0