While KVM_XEN_EVTCHN_RESET is usually called with no vCPUs running,
if that happened it could cause a deadlock. This is due to
kvm_xen_eventfd_reset() doing a synchronize_srcu() inside
a kvm->lock critical section.
To avoid this, first collect all the evtchnfd objects in an
array and free all of them once the kvm->lock critical section
is over and th SRCU grace period has expired.
Reported-by: Michal Luczaj <mhal@xxxxxxx>
Cc: David Woodhouse <dwmw@xxxxxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
arch/x86/kvm/xen.c | 30 +++++++++++++++++--
.../selftests/kvm/x86_64/xen_shinfo_test.c | 6 ++++
2 files changed, 33 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
index b178f40bd863..2e29bdc2949c 100644
--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -1942,18 +1942,42 @@ static int kvm_xen_eventfd_deassign(struct kvm *kvm, u32 port)
static int kvm_xen_eventfd_reset(struct kvm *kvm)
{
- struct evtchnfd *evtchnfd;
+ struct evtchnfd *evtchnfd, **all_evtchnfds;
int i;
+ int n = 0;
mutex_lock(&kvm->lock);
+
+ /*
+ * Because synchronize_srcu() cannot be called inside the
+ * critical section, first collect all the evtchnfd objects
+ * in an array as they are removed from evtchn_ports.
+ */
+ idr_for_each_entry(&kvm->arch.xen.evtchn_ports, evtchnfd, i)
+ n++;
+
+ all_evtchnfds = kmalloc_array(n, sizeof(struct evtchnfd *), GFP_KERNEL);
+ if (!all_evtchnfds) {
+ mutex_unlock(&kvm->lock);
+ return -ENOMEM;
+ }
+
+ n = 0;
idr_for_each_entry(&kvm->arch.xen.evtchn_ports, evtchnfd, i) {
+ all_evtchnfds[n++] = evtchnfd;
idr_remove(&kvm->arch.xen.evtchn_ports, evtchnfd->send_port);
- synchronize_srcu(&kvm->srcu);
+ }
+ mutex_unlock(&kvm->lock);
+
+ synchronize_srcu(&kvm->srcu);
+
+ while (n--) {
+ evtchnfd = all_evtchnfds[n];
if (!evtchnfd->deliver.port.port)
eventfd_ctx_put(evtchnfd->deliver.eventfd.ctx);
kfree(evtchnfd);
}
- mutex_unlock(&kvm->lock);
+ kfree(all_evtchnfds);
return 0;
}
diff --git a/tools/testing/selftests/kvm/x86_64/xen_shinfo_test.c b/tools/testing/selftests/kvm/x86_64/xen_shinfo_test.c
index 721f6a693799..dae510c263b4 100644
--- a/tools/testing/selftests/kvm/x86_64/xen_shinfo_test.c
+++ b/tools/testing/selftests/kvm/x86_64/xen_shinfo_test.c
@@ -962,6 +962,12 @@ int main(int argc, char *argv[])
}
done:
+ struct kvm_xen_hvm_attr evt_reset = {
+ .type = KVM_XEN_ATTR_TYPE_EVTCHN,
+ .u.evtchn.flags = KVM_XEN_EVTCHN_RESET,
+ };
+ vm_ioctl(vm, KVM_XEN_HVM_SET_ATTR, &evt_reset);
+
alarm(0);
clock_gettime(CLOCK_REALTIME, &max_ts);
--
2.31.1
