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SubjectRe: [PATCH v13 13/14] KVM: selftests: Let dirty_log_test async for dirty ring test
Date
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);
}
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