Re: [PATCH v13 13/14] KVM: selftests: Let dirty_log_test async for dirty ring test

[Paolo Bonzini]

On 01/10/20 03:22, Peter Xu wrote:
+
+static void vcpu_sig_handler(int sig)
+{
+       TEST_ASSERT(sig == SIG_IPI, "unknown signal: %d", sig);
+}
+

Unless you also use run->immediate_exit in vcpu_kick, this is racy.  The 
alternative is to _not_ set up a signal handler and instead block the 
signal.  KVM_SET_SIGNAL_MASK unblocks the signal inside the VM and on 
-EINTR sigwait accepts the signal (removes it from the set of pending 
signal).

This is a bit more complicated, but I think it's a good idea to do it 
this way for documentation purposes.  Here is the patch:

diff --git a/tools/testing/selftests/kvm/dirty_log_test.c 
b/tools/testing/selftests/kvm/dirty_log_test.c
index 4b404dfdc2f9..9a5b876b74af 100644
--- a/tools/testing/selftests/kvm/dirty_log_test.c
+++ b/tools/testing/selftests/kvm/dirty_log_test.c
@@ -172,11 +172,6 @@ static pthread_t vcpu_thread;
 /* Only way to pass this to the signal handler */
 static struct kvm_vm *current_vm;

-static void vcpu_sig_handler(int sig)
-{
-       TEST_ASSERT(sig == SIG_IPI, "unknown signal: %d", sig);
-}
-
 static void vcpu_kick(void)
 {
        pthread_kill(vcpu_thread, SIG_IPI);
@@ -484,13 +479,26 @@ static void *vcpu_worker(void *data)
        struct kvm_vm *vm = data;
        uint64_t *guest_array;
        uint64_t pages_count = 0;
-       struct sigaction sigact;
+	struct kvm_signal_mask *sigmask = alloca(offsetof(struct 
kvm_signal_mask, sigset)
+                                                + sizeof(sigset_t));
+       sigset_t *sigset = (sigset_t *) &sigmask->sigset;

        current_vm = vm;
        vcpu_fd = vcpu_get_fd(vm, VCPU_ID);
-       memset(&sigact, 0, sizeof(sigact));
-       sigact.sa_handler = vcpu_sig_handler;
-       sigaction(SIG_IPI, &sigact, NULL);
+
+       /*
+        * SIG_IPI is unblocked atomically while in KVM_RUN.  It causes the
+        * ioctl to return with -EINTR, but it is still pending and we need
+        * to accept it with the sigwait.
+        */
+       sigmask->len = 8;
+       pthread_sigmask(0, NULL, sigset);
+       vcpu_ioctl(vm, VCPU_ID, KVM_SET_SIGNAL_MASK, sigmask);
+       sigaddset(sigset, SIG_IPI);
+       pthread_sigmask(SIG_BLOCK, sigset, NULL);
+
+       sigemptyset(sigset);
+       sigaddset(sigset, SIG_IPI);

        guest_array = addr_gva2hva(vm, (vm_vaddr_t)random_array);

@@ -500,6 +508,11 @@ static void *vcpu_worker(void *data)
                pages_count += TEST_PAGES_PER_LOOP;
                /* Let the guest dirty the random pages */
                ret = ioctl(vcpu_fd, KVM_RUN, NULL);
+               if (ret == -EINTR) {
+                       int sig = -1;
+                       sigwait(sigset, &sig);
+                       assert(sig == SIG_IPI);
+               }
                log_mode_after_vcpu_run(vm, ret, errno);
        }