From: Paolo Bonzini pbonzini@redhat.com
[ Upstream commit a79b53aaaab53de017517bf9579b6106397a523c ]
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@rbox.co Cc: David Woodhouse dwmw@amazon.co.uk Signed-off-by: Paolo Bonzini pbonzini@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- 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 f3098c0e386a8..a58a426e6b1c0 100644 --- a/arch/x86/kvm/xen.c +++ b/arch/x86/kvm/xen.c @@ -1757,18 +1757,42 @@ 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 2a5727188c8d3..8383457e66990 100644 --- a/tools/testing/selftests/kvm/x86_64/xen_shinfo_test.c +++ b/tools/testing/selftests/kvm/x86_64/xen_shinfo_test.c @@ -942,6 +942,12 @@ 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);