On Thu, Feb 20, 2020 at 02:11:39PM +0800, Jason Wang wrote: > vDPA device is a device that uses a datapath which complies with the > virtio specifications with vendor specific control path. vDPA devices > can be both physically located on the hardware or emulated by > software. vDPA hardware devices are usually implemented through PCIE > with the following types: > > - PF (Physical Function) - A single Physical Function > - VF (Virtual Function) - Device that supports single root I/O > virtualization (SR-IOV). Its Virtual Function (VF) represents a > virtualized instance of the device that can be assigned to different > partitions > - ADI (Assignable Device Interface) and its equivalents - With > technologies such as Intel Scalable IOV, a virtual device (VDEV) > composed by host OS utilizing one or more ADIs. Or its equivalent > like SF (Sub function) from Mellanox. > > From a driver's perspective, depends on how and where the DMA > translation is done, vDPA devices are split into two types: > > - Platform specific DMA translation - From the driver's perspective, > the device can be used on a platform where device access to data in > memory is limited and/or translated. An example is a PCIE vDPA whose > DMA request was tagged via a bus (e.g PCIE) specific way. DMA > translation and protection are done at PCIE bus IOMMU level. > - Device specific DMA translation - The device implements DMA > isolation and protection through its own logic. An example is a vDPA > device which uses on-chip IOMMU. > > To hide the differences and complexity of the above types for a vDPA > device/IOMMU options and in order to present a generic virtio device > to the upper layer, a device agnostic framework is required. > > This patch introduces a software vDPA bus which abstracts the > common attributes of vDPA device, vDPA bus driver and the > communication method (vdpa_config_ops) between the vDPA device > abstraction and the vDPA bus driver. This allows multiple types of > drivers to be used for vDPA device like the virtio_vdpa and vhost_vdpa > driver to operate on the bus and allow vDPA device could be used by > either kernel virtio driver or userspace vhost drivers as: > > virtio drivers vhost drivers > | | > [virtio bus] [vhost uAPI] > | | > virtio device vhost device > virtio_vdpa drv vhost_vdpa drv > \ / > [vDPA bus] > | > vDPA device > hardware drv > | > [hardware bus] > | > vDPA hardware I still don't like this strange complexity, vhost should have been layered on top of the virtio device instead of adding an extra bus just for vdpa. However, I don't see any technical problems with this patch now. Thanks, Jason
