Re: [virtio-dev] [PATCH v5 03/10] vhost-user: add requirements for the notification capability

[Nikos Dragazis <ndragazis@arrikto.com>]

On 17/7/20 12:34 Î.Î., Stefan Hajnoczi wrote:

> On Mon, May 18, 2020 at 11:37:14PM +0300, Nikos Dragazis wrote:
> > The configuration structure for the notification capability has certain
> > device/driver requirements, similar to those of the MSI-X vector
> > configuration. Add these requirements to the device spec.
> >
> > Signed-off-by: Nikos Dragazis <ndragazis@arrikto.com>
> > ---
> >   virtio-vhost-user.tex | 42 ++++++++++++++++++++++++++++++++++++++++++
> >   1 file changed, 42 insertions(+)
> >
> > diff --git a/virtio-vhost-user.tex b/virtio-vhost-user.tex
> > index 13ecd41..7a8cd9c 100644
> > --- a/virtio-vhost-user.tex
> > +++ b/virtio-vhost-user.tex
> > @@ -275,6 +275,48 @@ \subsubsection{Notification structure layout}\label{sec:Device Types / Vhost-use
> >   \field{VIRTIO_MSI_NO_VECTOR} to \field{notification_msix_vector} to change the
> >   MSI-X vector for that notification.
> >   
> > +\devicenormative{\paragraph}{Notification capability}{Device Types / Vhost-user Device Backend / Additional Device Resources over PCI / Notification capability}
> > +
> > +If MSI-X is available, device MUST support mapping any master queue
> > +event to any valid vector 0 to MSI-X \field{Table Size}. Here
> This section combines two things:
> 1. vhost-user concepts -> VIRTIO notifications
> 2. VIRTIO notifications -> VIRTIO PCI transport MSI-X implementation of
>     notifications
>
> I think this should be split:
> 1. The virtio-vhost-user device spec should explain that vhost-user queue
>     events are mapped to VIRTIO notifications
> 2. The PCI transport spec should explain how notifications are mapped to
>     MSI-X
>
> This way other VIRTIO device types will be able to use notifications too
> without everyone explaining MSI-X specifics. Also it won't tie
> virtio-vhost-user to VIRTIO PCI.

If I understand correctly, you are suggesting that we should standardize
the notification resource, similarly to the shared memory resource, so
that any device can use it. Is that so?

> > +\field{Table Size} is the \field{N-1} encoded Table Size stored in the
> > +Message Control register of the MSI-X capability structure according to
> > +\hyperref[intro:PCI]{[PCI]}, where \field{N} is the actual MSI-X Table
> > +Size.
> > +
> > +Device MUST support unmapping any master queue event.
> > +
> > +The device MUST return vector mapped to a given master queue event,
> > +(\field{NO_VECTOR} if unmapped) on read of
> > +\field{notification_msix_vector}. The device MUST have all master queue
> > +events unmapped upon reset.
> "The device MUST unmap all master queue events upon reset" is clearer in
> indicating that the device must take this action.

ACK