On Sun, Jan 30, 2022 at 11:56:30AM +0200, Max Gurtovoy wrote: > > On 1/30/2022 11:40 AM, Michael S. Tsirkin wrote: > > On Sun, Jan 30, 2022 at 11:13:38AM +0200, Max Gurtovoy wrote: > > > On 1/29/2022 5:53 AM, Jason Wang wrote: > > > > On Fri, Jan 28, 2022 at 11:52 PM Michael S. Tsirkin <[email protected]> > > > > wrote: > > > > > On Fri, Jan 28, 2022 at 04:49:34PM +0100, Cornelia Huck wrote: > > > > > > On Fri, Jan 28 2022, "Michael S. Tsirkin" <[email protected]> wrote: > > > > > > > > > > > > > On Fri, Jan 28, 2022 at 01:14:14PM +0100, Cornelia Huck wrote: > > > > > > > > On Mon, Jan 24 2022, Max Gurtovoy <[email protected]> wrote: > > > > > > > > > +\section{Admin Virtqueues}\label{sec:Basic Facilities of a > > > > > > > > > Virtio Device / Admin Virtqueues} > > > > > > > > > + > > > > > > > > > +Admin virtqueue is used to send administrative commands to > > > > > > > > > manipulate > > > > > > > > > +various features of the device and/or to manipulate various > > > > > > > > > features, > > > > > > > > > +if possible, of another device within the same group (e.g. > > > > > > > > > PCI VFs of > > > > > > > > > +a parent PCI PF device are grouped together. These devices > > > > > > > > > can be > > > > > > > > > +optionally managed by its parent PCI PF using its admin > > > > > > > > > virtqueue.). > > > > > > > > > + > > > > > > > > > +Use of Admin virtqueue is negotiated by the VIRTIO_F_ADMIN_VQ > > > > > > > > > +feature bit. > > > > > > > > > + > > > > > > > > > +Admin virtqueue index may vary among different device types. > > > > > > > > So, my understanding is: > > > > > > > > - any device type may or may not support the admin vq > > > > > > > > - if the device type wants to be able to accommodate the admin > > > > > > > > vq, it > > > > > > > > also needs to specify where it shows up when the feature is > > > > > > > > negotiated > > > > > > > > > > > > > > > > Do we expect that eventually all device types will need to > > > > > > > > support the > > > > > > > > admin vq (if some use case comes along that will require all > > > > > > > > devices to > > > > > > > > participate, for example?) > > > > > > > I suspect yes. And that's one of the reasons why I'd rather we > > > > > > > had a > > > > > > > device independent way to locate the admin queue. There are less > > > > > > > transports than device types. > > > > > > So, do we want to bite the bullet now and simply say that every > > > > > > device > > > > > > type has the admin vq as the last vq if the feature is negotiated? > > > > > > Should be straightforward for the device types that have a fixed > > > > > > number > > > > > > of vqs, and doable for those that have a variable amount (two device > > > > > > types are covered by this series anyway.) I think we need to put it > > > > > > with > > > > > > the device types, as otherwise the numbering of virtqueues could > > > > > > change > > > > > > in unpredictable ways with the admin vq off/on. > > > > > Well that only works once. The next thing we'll need we won't be able > > > > > to > > > > > make the last one ;) So I am inclined to add a per-transport field > > > > > that > > > > > gives the admin queue number. > > > > Technically, there's no need to use the same namespace for admin > > > > virtqueue if it has a dedicated notification area. If we go this way, > > > > we can simply use 0 as queue index for admin virtqueue. > > > Or we can use index 0xFFFF for admin virtqueue for compatibility. > > I think I'd prefer a register with the #. For example we might want > > to limit the # of VQs in order to pass extra data with the kick write. > > So you are suggesting adding a new cfg_type (#define > VIRTIO_PCI_CAP_ADMIN_CFG 10) ? > > that will look something like: > > struct virtio_pci_admin_cfg { > > le32 queue_index; /* read only for the driver */ > > le16 queue_size; /* read-write */ > le16 queue_msix_vector; /* read-write */ > le16 queue_enable; /* read-write */ > le16 queue_notify_off; /* read-only for driver */ > le64 queue_desc; /* read-write */ > le64 queue_driver; /* read-write */ > le64 queue_device; /* read-write */ > le16 queue_notify_data; /* read-only for driver */ > le16 queue_reset; /* read-write */ > > }; > > instead of re-using the struct virtio_pci_common_cfg ? > > > or do you prefer extending the struct virtio_pci_common_cfg with "le16 > admin_queue_index; /* read only for the driver */ ?
The later. Other transports will need this too. Cornelia has another idea which is that instead of adding just the admin queue register to all transports, we instead add a misc_config structure to all transports. Working basically like device specific config, but being device independent. For now it will only have a single le16 admin_queue_index register. For PCI we would thus add it with VIRTIO_PCI_CAP_MISC_CFG The point here is that we are making it easier to add more fields just like admin queue index in the future. > > > > > > > > Thanks > > > > > > > > > Another advantage to this approach is that > > > > > we can make sure admin queue gets a page by itself (which can be good > > > > > if > > > > > we want to allow access to regular vqs but not to the admin queue to > > > > > guest) even if regular vqs share a page. Will help devices use less > > > > > memory space. > > > > > > > > > > -- > > > > > MST > > > > > --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
