Re: [PATCH v3 1/2] KVM: selftests: Sync data verify of dirty logging with guest sync

[Paolo Bonzini]

On 20/04/21 15:10, Peter Xu wrote:

On Tue, Apr 20, 2021 at 10:07:16AM +0200, Paolo Bonzini wrote:

On 18/04/21 14:43, Peter Xu wrote:

----8<-----
diff --git a/tools/testing/selftests/kvm/dirty_log_test.c 
b/tools/testing/selftests/kvm/dirty_log_test.c
index 25230e799bc4..d3050d1c2cd0 100644
--- a/tools/testing/selftests/kvm/dirty_log_test.c
+++ b/tools/testing/selftests/kvm/dirty_log_test.c
@@ -377,7 +377,7 @@ static void dirty_ring_after_vcpu_run(struct kvm_vm *vm, 
int ret, int err)
          /* A ucall-sync or ring-full event is allowed */
          if (get_ucall(vm, VCPU_ID, NULL) == UCALL_SYNC) {
                  /* We should allow this to continue */
-               ;
+               vcpu_handle_sync_stop();
          } else if (run->exit_reason == KVM_EXIT_DIRTY_RING_FULL ||
                     (ret == -1 && err == EINTR)) {
                  /* Update the flag first before pause */
----8<-----

That's my intention when I introduce vcpu_handle_sync_stop(), but forgot to
add...

And possibly even this (untested though):

diff --git a/tools/testing/selftests/kvm/dirty_log_test.c 
b/tools/testing/selftests/kvm/dirty_log_test.c
index ffa4e2791926..918954f01cef 100644
--- a/tools/testing/selftests/kvm/dirty_log_test.c
+++ b/tools/testing/selftests/kvm/dirty_log_test.c
@@ -383,6 +383,7 @@ static void dirty_ring_after_vcpu_run(struct kvm_vm *vm, 
int ret, int err)
                /* Update the flag first before pause */
                WRITE_ONCE(dirty_ring_vcpu_ring_full,
                           run->exit_reason == KVM_EXIT_DIRTY_RING_FULL);
+               atomic_set(&vcpu_sync_stop_requested, false);
                sem_post(&sem_vcpu_stop);
                pr_info("vcpu stops because %s...\n",
                        dirty_ring_vcpu_ring_full ?
@@ -804,8 +805,7 @@ static void run_test(enum vm_guest_mode mode, void *arg)
                 * the flush of the last page, and since we handle the last
                 * page specially verification will succeed anyway.
                 */
-               assert(host_log_mode == LOG_MODE_DIRTY_RING ||
-                      atomic_read(&vcpu_sync_stop_requested) == false);
+               assert(atomic_read(&vcpu_sync_stop_requested) == false);
                vm_dirty_log_verify(mode, bmap);
                sem_post(&sem_vcpu_cont);

You can submit all these as a separate patch.

But it could race, then?

         main thread                 vcpu thread
         -----------                 -----------
                                   ring full
                                     vcpu_sync_stop_requested=0
                                     sem_post(&sem_vcpu_stop)
      vcpu_sync_stop_requested=1
      sem_wait(&sem_vcpu_stop)
      assert(vcpu_sync_stop_requested==0)   <----

Yes, it could indeed.

Thanks,

Paolo