[virtio-dev] Re: [PATCH v12 05/10] pci: add admin vq registers to virtio over pci

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Apr 27, 2023 at 01:31:29AM +0300, Max Gurtovoy wrote:
> 
> 
> On 27/04/2023 1:11, Parav Pandit wrote:
> > 
> > > From: Max Gurtovoy <mgurtovoy@nvidia.com>
> > > Sent: Wednesday, April 26, 2023 5:12 PM
> > > 
> > > On 25/04/2023 1:14, Parav Pandit wrote:
> > > > 
> > > > 
> > > > On 4/24/2023 6:06 PM, Max Gurtovoy wrote:
> > > > 
> > > > > > +If VIRTIO_F_ADMIN_VQ has been negotiated, and if the driver
> > > > > > +configures any administration virtqueues, the driver MUST configure
> > > > > > +the administration virtqueues using the index in the range
> > > > > > +\field{admin_queue_index} to \field{admin_queue_index} +
> > > > > > +\field{admin_queue_num} - 1 inclusive.
> > > > > > +The driver MAY configure less administration virtqueues than
> > > > > > +supported by the device.
> > > > > 
> > > > > we need to say something about other virtq's indexes.
> > > > > For example, if aq index = 0 then for the vblk device the request
> > > > > queues would start from index = 1.
> > > > > 
> > > > > can we address this ?
> > > > 
> > > > It may slightly complicate the device implementation when device
> > > > dynamically changes the VQ indices based on the negotiation of the
> > > > feature bit.
> > > > Also the drivers with and without need a different VQ index handling.
> > > > 
> > > > I am thinking that aq index should not overlap with the vq index in
> > > > range exposed by num_queues field.
> > > > 
> > > > This also aligns to the exclusion of aq count from num_queues field.
> > > 
> > > The namespace of the aq and other vq index is the same.
> > > And the configuration is done using the same queue_select and other registers.
> > > Thus, we need to address the above comment otherwise all the device
> > > virtqueues chapters are wrong.
> > 
> > Michael has added below line in this patch in num_queues description so it covers the exclusion part.
> > 
> > +        This excludes administration virtqueues if any are supported.
> > 
> 
> This is not related to what I was talking about.
> 
> For example if vnet device:
> 
> 0 receiveq1
> 1 transmitq1
> ...
> 2(N-1) receiveqN
> 2(N-1)+1 transmitqN
> 2N controlq
> N=1 if neither VIRTIO_NET_F_MQ nor VIRTIO_NET_F_RSS are negotiated,
> otherwise N is set by max_-
> virtqueue_pairs.
> controlq only exists if VIRTIO_NET_F_CTRL_VQ set
> 
> and in vfs device:
> 
> 0 hiprio
> 1...n request queues
> 
> So if one device will expose adminq that will be with index 0 the above is
> wrong description.
> 
> Agree that this should be addressed ?

It's addressed by patch 9:


+If VIRTIO_F_ADMIN_VQ has been negotiated, the value
+\field{admin_queue_index} MUST be equal to, or bigger than
+\field{num_queues}; also, \field{admin_queue_num} MUST be
+smaller than, or equal to 0x10000 - \field{admin_queue_index},
+to ensure that indices of valid admin queues fit into
+a 16 bit range beyond all other virtqueues.


Thus adminq can not have index 0.

-- 
MST


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