Jason Wang
2021-Nov-04 02:34 UTC
[RFC PATCH v5 21/26] vhost: Add vhost_svq_valid_guest_features to shadow vq
On Wed, Nov 3, 2021 at 3:44 PM Eugenio Perez Martin <eperezma at redhat.com> wrote:> > On Wed, Nov 3, 2021 at 4:18 AM Jason Wang <jasowang at redhat.com> wrote: > > > > On Tue, Nov 2, 2021 at 4:10 PM Eugenio Perez Martin <eperezma at redhat.com> wrote: > > > > > > On Tue, Nov 2, 2021 at 6:26 AM Jason Wang <jasowang at redhat.com> wrote: > > > > > > > > On Sat, Oct 30, 2021 at 2:44 AM Eugenio P?rez <eperezma at redhat.com> wrote: > > > > > > > > > > This allows it to test if the guest has aknowledge an invalid transport > > > > > feature for SVQ. This will include packed vq layout or event_idx, > > > > > where VirtIO device needs help from SVQ. > > > > > > > > > > There is not needed at this moment, but since SVQ will not re-negotiate > > > > > features again with the guest, a failure in acknowledge them is fatal > > > > > for SVQ. > > > > > > > > > > > > > It's not clear to me why we need this. Maybe you can give me an > > > > example. E.g isn't it sufficient to filter out the device with > > > > event_idx? > > > > > > > > > > If the guest did negotiate _F_EVENT_IDX, it expects to be notified > > > only when device marks as used a specific number of descriptors. > > > > > > If we use VirtQueue notification, the VirtQueue code handles it > > > transparently. But if we want to be able to change the guest VQ's > > > call_fd, we cannot use VirtQueue's, so this needs to be handled by SVQ > > > code. And that is still not implemented. > > > > > > Of course in the event_idx case we could just ignore it and notify in > > > all used descriptors, but it seems not polite to me :). I will develop > > > event_idx on top of this, either exposing the needed pieces in > > > VirtQueue (I prefer this) or rolling our own in SVQ. > > > > Yes, but what I meant is, we can fail the SVQ enabling if the device > > supports event_idx. Then we're sure guests won't negotiate event_idx. > > > > We can go that way for sure, but then we leave out the scenario where > the device supports event_idx but the guest has not acked it. This is > a valid scenario for SVQ to work in.If SVQ supports event idx in the future, we can remove it from the blacklist. But I think it should be simpler to let SVQ use the same features as guests. So in this case SVQ won't use the event index. Thanks> > Thanks! > > > Thanks > > > > > > > > Same reasoning can be applied to unknown transport features. > > > > > > Thanks! > > > > > > > Thanks > > > > > > > > > Signed-off-by: Eugenio P?rez <eperezma at redhat.com> > > > > > --- > > > > > hw/virtio/vhost-shadow-virtqueue.h | 1 + > > > > > hw/virtio/vhost-shadow-virtqueue.c | 6 ++++++ > > > > > 2 files changed, 7 insertions(+) > > > > > > > > > > diff --git a/hw/virtio/vhost-shadow-virtqueue.h b/hw/virtio/vhost-shadow-virtqueue.h > > > > > index 946b2c6295..ac55588009 100644 > > > > > --- a/hw/virtio/vhost-shadow-virtqueue.h > > > > > +++ b/hw/virtio/vhost-shadow-virtqueue.h > > > > > @@ -16,6 +16,7 @@ > > > > > typedef struct VhostShadowVirtqueue VhostShadowVirtqueue; > > > > > > > > > > bool vhost_svq_valid_device_features(uint64_t *features); > > > > > +bool vhost_svq_valid_guest_features(uint64_t *features); > > > > > > > > > > void vhost_svq_set_svq_kick_fd(VhostShadowVirtqueue *svq, int svq_kick_fd); > > > > > void vhost_svq_set_guest_call_notifier(VhostShadowVirtqueue *svq, int call_fd); > > > > > diff --git a/hw/virtio/vhost-shadow-virtqueue.c b/hw/virtio/vhost-shadow-virtqueue.c > > > > > index 6e0508a231..cb9ffcb015 100644 > > > > > --- a/hw/virtio/vhost-shadow-virtqueue.c > > > > > +++ b/hw/virtio/vhost-shadow-virtqueue.c > > > > > @@ -62,6 +62,12 @@ bool vhost_svq_valid_device_features(uint64_t *dev_features) > > > > > return true; > > > > > } > > > > > > > > > > +/* If the guest is using some of these, SVQ cannot communicate */ > > > > > +bool vhost_svq_valid_guest_features(uint64_t *guest_features) > > > > > +{ > > > > > + return true; > > > > > +} > > > > > + > > > > > /* Forward guest notifications */ > > > > > static void vhost_handle_guest_kick(EventNotifier *n) > > > > > { > > > > > -- > > > > > 2.27.0 > > > > > > > > > > > > > > >