From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Sun, 30 Jan 2022 10:30:32 -0500 From: "Michael S. Tsirkin" Subject: Re: [PATCH v2 1/4] Add virtio Admin Virtqueue Message-ID: <20220130102940-mutt-send-email-mst@kernel.org> References: <87wnikys4p.fsf@redhat.com> <20220128074613-mutt-send-email-mst@kernel.org> <87tudnzwq9.fsf@redhat.com> <20220128105012-mutt-send-email-mst@kernel.org> <20220130043917-mutt-send-email-mst@kernel.org> <20220130093740-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="iso-8859-1" Content-Disposition: inline Content-Transfer-Encoding: quoted-printable To: Max Gurtovoy Cc: Jason Wang , Cornelia Huck , virtio-comment@lists.oasis-open.org, Virtio-Dev , Parav Pandit , Shahaf Shuler , Oren Duer , Stefan Hajnoczi List-ID: On Sun, Jan 30, 2022 at 05:12:46PM +0200, Max Gurtovoy wrote: >=20 > On 1/30/2022 4:41 PM, Michael S. Tsirkin wrote: > > 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 wrote: > > > > > > > On Fri, Jan 28, 2022 at 04:49:34PM +0100, Cornelia Huck wrote: > > > > > > > > On Fri, Jan 28 2022, "Michael S. Tsirkin" = wrote: > > > > > > > >=20 > > > > > > > > > On Fri, Jan 28, 2022 at 01:14:14PM +0100, Cornelia Huck w= rote: > > > > > > > > > > On Mon, Jan 24 2022, Max Gurtovoy wrote: > > > > > > > > > > > +\section{Admin Virtqueues}\label{sec:Basic Facilitie= s of a Virtio Device / Admin Virtqueues} > > > > > > > > > > > + > > > > > > > > > > > +Admin virtqueue is used to send administrative comma= nds 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 d= evices can be > > > > > > > > > > > +optionally managed by its parent PCI PF using its ad= min virtqueue.). > > > > > > > > > > > + > > > > > > > > > > > +Use of Admin virtqueue is negotiated by the VIRTIO_F= _ADMIN_VQ > > > > > > > > > > > +feature bit. > > > > > > > > > > > + > > > > > > > > > > > +Admin virtqueue index may vary among different devic= e 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 th= e admin vq, it > > > > > > > > > > also needs to specify where it shows up when the f= eature is negotiated > > > > > > > > > >=20 > > > > > > > > > > Do we expect that eventually all device types will need= to support the > > > > > > > > > > admin vq (if some use case comes along that will requir= e all devices to > > > > > > > > > > participate, for example?) > > > > > > > > > I suspect yes. And that's one of the reasons why I'd rath= er we had a > > > > > > > > > device independent way to locate the admin queue. There a= re less > > > > > > > > > transports than device types. > > > > > > > > So, do we want to bite the bullet now and simply say that e= very device > > > > > > > > type has the admin vq as the last vq if the feature is nego= tiated? > > > > > > > > Should be straightforward for the device types that have a = fixed number > > > > > > > > of vqs, and doable for those that have a variable amount (t= wo device > > > > > > > > types are covered by this series anyway.) I think we need t= o 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 thi= s 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 wri= te. > > > So you are suggesting adding a new cfg_type (#define > > > VIRTIO_PCI_CAP_ADMIN_CFG 10) ? > > >=20 > > > that will look something like: > > >=20 > > > struct virtio_pci_admin_cfg { > > >=20 > > > =A0=A0=A0 le32 queue_index; /* read only for the driver */ > > >=20 > > > =A0=A0=A0 le16 queue_size; /* read-write */ > > > =A0=A0=A0 le16 queue_msix_vector; /* read-write */ > > > =A0=A0=A0 le16 queue_enable; /* read-write */ > > > =A0=A0=A0 le16 queue_notify_off; /* read-only for driver */ > > > =A0=A0=A0 le64 queue_desc; /* read-write */ > > > =A0=A0=A0 le64 queue_driver; /* read-write */ > > > =A0=A0=A0 le64 queue_device; /* read-write */ > > > =A0=A0=A0 le16 queue_notify_data; /* read-only for driver */ > > > =A0=A0=A0 le16 queue_reset; /* read-write */ > > >=20 > > > }; > > >=20 > > > instead of re-using the struct virtio_pci_common_cfg ? > > >=20 > > >=20 > > > 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. > >=20 > >=20 > > 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. > >=20 > > For PCI we would thus add it with VIRTIO_PCI_CAP_MISC_CFG > >=20 > > The point here is that we are making it easier to add > > more fields just like admin queue index in the future. >=20 > OK. >=20 > #define VIRTIO_PCI_CAP_MISC_CFG 10 >=20 > and >=20 > struct virtio_pci_misc_cfg { > le16 admin_queue_index; /* read-only for driver */ > }; >=20 > Is agreed by all for V3 ? instead of the net and blk AQ index definitions. We need to add it to MMIO and CCW I guess too. This is Cornelia's idea, we'll need her response. >=20 > >=20 > >=20 > > > >=20 > > > > > > Thanks > > > > > >=20 > > > > > > > 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 q= ueue to > > > > > > > guest) even if regular vqs share a page. Will help devices us= e less > > > > > > > memory space. > > > > > > >=20 > > > > > > > -- > > > > > > > MST > > > > > > >=20