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Tsirkin" To: Jason Wang Subject: Re: [RFC 02/10] vhost: add 3 commands for vhost-vdpa Message-ID: <20220105072321-mutt-send-email-mst@kernel.org> References: <20220105005900.860-1-longpeng2@huawei.com> <20220105005900.860-3-longpeng2@huawei.com> <20220105020008-mutt-send-email-mst@kernel.org> <1d157f74fdac49ff8ae734808bd3c518@huawei.com> MIME-Version: 1.0 In-Reply-To: Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mst@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=170.10.129.124; envelope-from=mst@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -31 X-Spam_score: -3.2 X-Spam_bar: --- X-Spam_report: (-3.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.372, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Cornelia Huck , qemu-devel , Yechuan , "Gonglei \(Arei\)" , Huangzhichao , Stefan Hajnoczi , pbonzini , "Longpeng \(Mike, Cloud Infrastructure Service Product Dept.\)" , Stefano Garzarella Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, Jan 05, 2022 at 05:09:07PM +0800, Jason Wang wrote: > On Wed, Jan 5, 2022 at 4:37 PM Longpeng (Mike, Cloud Infrastructure > Service Product Dept.) wrote: > > > > > > > > > -----Original Message----- > > > From: Jason Wang [mailto:jasowang@redhat.com] > > > Sent: Wednesday, January 5, 2022 3:54 PM > > > To: Michael S. Tsirkin > > > Cc: Longpeng (Mike, Cloud Infrastructure Service Product Dept.) > > > ; Stefan Hajnoczi ; Stefano > > > Garzarella ; Cornelia Huck ; pbonzini > > > ; Gonglei (Arei) ; Yechuan > > > ; Huangzhichao ; qemu-devel > > > > > > Subject: Re: [RFC 02/10] vhost: add 3 commands for vhost-vdpa > > > > > > On Wed, Jan 5, 2022 at 3:02 PM Michael S. Tsirkin wrote: > > > > > > > > On Wed, Jan 05, 2022 at 12:35:53PM +0800, Jason Wang wrote: > > > > > On Wed, Jan 5, 2022 at 8:59 AM Longpeng(Mike) wrote: > > > > > > > > > > > > From: Longpeng > > > > > > > > > > > > To support generic vdpa deivce, we need add the following ioctls: > > > > > > - GET_VECTORS_NUM: the count of vectors that supported > > > > > > > > > > Does this mean MSI vectors? If yes, it looks like a layer violation: > > > > > vhost is transport independent. > > > > > > > > Well *guest* needs to know how many vectors device supports. > > > > I don't think there's a way around that. Do you? > > > > > > We have VHOST_SET_VRING/CONFIG_CALL which is per vq. I think we can > > > simply assume #vqs + 1? > > > > > > > Otherwise guests will at best be suboptimal. > > > > > > > > > And it reveals device implementation > > > > > details which block (cross vendor) migration. > > > > > > > > > > Thanks > > > > > > > > Not necessarily, userspace can hide this from guest if it > > > > wants to, just validate. > > > > > > If we can hide it at vhost/uAPI level, it would be even better? > > > > > > > Not only MSI vectors, but also queue-size, #vqs, etc. > > MSI is PCI specific, we have non PCI vDPA parent e.g VDUSE/simulator/mlx5 > > And it's something that is not guaranteed to be not changed. E.g some > drivers may choose to allocate MSI during set_status() which can fail > for various reasons. > > > > > Maybe the vhost level could expose the hardware's real capabilities > > and let the userspace (QEMU) do the hiding? The userspace know how > > to process them. > > #MSI vectors is much more easier to be mediated than queue-size and #vqs. > > For interrupts, we've already had VHOST_SET_X_KICK, we can keep > allocating eventfd based on #MSI vectors to make it work with any > number of MSI vectors that the virtual device had. Right but if hardware does not support so many then what? Just fail? Having a query API would make things somewhat cleaner imho. > For queue-size, it's Ok to have a new uAPI but it's not a must, Qemu > can simply fail if SET_VRING_NUM fail. > > For #vqs, it's OK to have a new uAPI since the emulated virtio-pci > device requires knowledge the #vqs in the config space. (still not a > must, we can enumerate #vqs per device type) > > For the config size, it's OK but not a must, technically we can simply > relay what guest write to vhost-vdpa. It's just because current Qemu > require to have it during virtio device initialization. > > Thanks I agree but these ok things make for a cleaner API I think. > > > > > Thanks > > > > > > > > > > > > > > > > > - GET_CONFIG_SIZE: the size of the virtio config space > > > > > > - GET_VQS_NUM: the count of virtqueues that exported > > > > > > > > > > > > Signed-off-by: Longpeng > > > > > > --- > > > > > > linux-headers/linux/vhost.h | 10 ++++++++++ > > > > > > 1 file changed, 10 insertions(+) > > > > > > > > > > > > diff --git a/linux-headers/linux/vhost.h b/linux-headers/linux/vhost.h > > > > > > index c998860d7b..c5edd75d15 100644 > > > > > > --- a/linux-headers/linux/vhost.h > > > > > > +++ b/linux-headers/linux/vhost.h > > > > > > @@ -150,4 +150,14 @@ > > > > > > /* Get the valid iova range */ > > > > > > #define VHOST_VDPA_GET_IOVA_RANGE _IOR(VHOST_VIRTIO, 0x78, \ > > > > > > struct vhost_vdpa_iova_range) > > > > > > + > > > > > > +/* Get the number of vectors */ > > > > > > +#define VHOST_VDPA_GET_VECTORS_NUM _IOR(VHOST_VIRTIO, 0x79, int) > > > > > > + > > > > > > +/* Get the virtio config size */ > > > > > > +#define VHOST_VDPA_GET_CONFIG_SIZE _IOR(VHOST_VIRTIO, 0x80, int) > > > > > > + > > > > > > +/* Get the number of virtqueues */ > > > > > > +#define VHOST_VDPA_GET_VQS_NUM _IOR(VHOST_VIRTIO, 0x81, int) > > > > > > + > > > > > > #endif > > > > > > -- > > > > > > 2.23.0 > > > > > > > > > > > >