On 11/13/2015 10:28 AM, Pavel Fedin wrote: > If you happen to have a stock kernel of old version, like 3.x, and you > attempt to enable vhost by setting vhost=on, qemu aborts with error: > > kvm_mem_ioeventfd_add: error adding ioeventfd: Function not implemented > > This patch adds capability check, so that vhost gets disabled instead. A > warning is displayed, explaining the reason. > > This problem can be observed with libvirt, which checks for /dev/vhost-net > availability and just inserts "vhost=on" automatically in this case. > > Signed-off-by: Pavel Fedin <p.fe...@samsung.com> > --- > hw/virtio/vhost.c | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c > index 1794f0d..3121e19 100644 > --- a/hw/virtio/vhost.c > +++ b/hw/virtio/vhost.c > @@ -24,6 +24,7 @@ > #include "hw/virtio/virtio-bus.h" > #include "hw/virtio/virtio-access.h" > #include "migration/migration.h" > +#include "sysemu/kvm.h" > > static struct vhost_log *vhost_log; > static struct vhost_log *vhost_log_shm; > @@ -1083,6 +1084,11 @@ int vhost_dev_enable_notifiers(struct vhost_dev *hdev, > VirtIODevice *vdev) > r = -ENOSYS; > goto fail; > } > + if (!kvm_eventfds_enabled()) { > + error_report("KVM does not support MMIO eventfds");
We also have virtio-ccw. what about something without MMIO like error_report("KVM does not support eventfds");