Re: [RFC PATCH v9 13/23] vhost: Add vhost_svq_inject

[Jason Wang]

在 2022/7/11 17:43, Eugenio Perez Martin 写道:
> On Mon, Jul 11, 2022 at 11:14 AM Jason Wang <jasowang@redhat.com> wrote:
> > 在 2022/7/7 02:39, Eugenio Pérez 写道:
> > > This allows qemu to inject buffers to the device.
> >
> > Not a native speaker but we probably need a better terminology than
> > inject here.
> >
> > Since the CVQ is totally under the control of the Qemu anyhow.
> I'm totally fine to change terminology
>
> > > Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
> > > ---
> > >    hw/virtio/vhost-shadow-virtqueue.h |  2 ++
> > >    hw/virtio/vhost-shadow-virtqueue.c | 34 ++++++++++++++++++++++++++++++
> > >    2 files changed, 36 insertions(+)
> > >
> > > diff --git a/hw/virtio/vhost-shadow-virtqueue.h 
> > > b/hw/virtio/vhost-shadow-virtqueue.h
> > > index a811f90e01..d01d2370db 100644
> > > --- a/hw/virtio/vhost-shadow-virtqueue.h
> > > +++ b/hw/virtio/vhost-shadow-virtqueue.h
> > > @@ -98,6 +98,8 @@ bool vhost_svq_valid_features(uint64_t features, Error 
> > > **errp);
> > >
> > >    void vhost_svq_push_elem(VhostShadowVirtqueue *svq,
> > >                             const VirtQueueElement *elem, uint32_t len);
> > > +int vhost_svq_inject(VhostShadowVirtqueue *svq, const struct iovec *iov,
> > > +                     size_t out_num, size_t in_num, void *opaque);
> > >    void vhost_svq_set_svq_kick_fd(VhostShadowVirtqueue *svq, int svq_kick_fd);
> > >    void vhost_svq_set_svq_call_fd(VhostShadowVirtqueue *svq, int call_fd);
> > >    void vhost_svq_get_vring_addr(const VhostShadowVirtqueue *svq,
> > > diff --git a/hw/virtio/vhost-shadow-virtqueue.c 
> > > b/hw/virtio/vhost-shadow-virtqueue.c
> > > index 492bb12b5f..bd9e34b413 100644
> > > --- a/hw/virtio/vhost-shadow-virtqueue.c
> > > +++ b/hw/virtio/vhost-shadow-virtqueue.c
> > > @@ -283,6 +283,40 @@ static bool vhost_svq_add_element(VhostShadowVirtqueue 
> > > *svq,
> > >        return ok;
> > >    }
> > >
> > > +/**
> > > + * Inject a chain of buffers to the device
> > > + *
> > > + * @svq: Shadow VirtQueue
> > > + * @iov: I/O vector
> > > + * @out_num: Number of front out descriptors
> > > + * @in_num: Number of last input descriptors
> > > + * @opaque: Contextual data to store in descriptor
> > > + *
> > > + * Return 0 on success, -ENOMEM if cannot inject
> > > + */
> > > +int vhost_svq_inject(VhostShadowVirtqueue *svq, const struct iovec *iov,
> > > +                     size_t out_num, size_t in_num, void *opaque)
> >
> > If we manage to embed opaque into VirtqueueElement, we can simply use
> > vhost_svq_add() here.
> That works fine as long as SVQ only forwards elements, but it needs to
> do more than that: We need to inject new elements without guest
> notice.
>
> How could we track elements that do not have corresponding
> VirtQueueElement, like the elements sent to restore the status at the
> LM destination?


Having a token for each VirtQueueElement will work? Or maybe I can ask 
differently, what kind of extra state that need to be tracked here?

(For virtio state it should be handled by shadow virtqueue core).

Thanks


> I'll try to make it clearer in the patch message.
>
> Thanks!
>
> > Thanks
> >
> >
> > > +{
> > > +    bool ok;
> > > +
> > > +    /*
> > > +     * All vhost_svq_inject calls are controlled by qemu so we won't hit this
> > > +     * assertions.
> > > +     */
> > > +    assert(out_num || in_num);
> > > +    assert(svq->ops);
> > > +
> > > +    if (unlikely(svq->next_guest_avail_elem)) {
> > > +        error_report("Injecting in a full queue");
> > > +        return -ENOMEM;
> > > +    }
> > > +
> > > +    ok = vhost_svq_add(svq, iov, out_num, iov + out_num, in_num, opaque);
> > > +    assert(ok);
> > > +    vhost_svq_kick(svq);
> > > +    return 0;
> > > +}
> > > +
> > >    /**
> > >     * Forward available buffers.
> > >     *