On Wed, Oct 23, 2019 at 01:46:23PM +0800, Jason Wang wrote: > On 2019/10/23 上午11:02, Tiwei Bie wrote: > > On Tue, Oct 22, 2019 at 09:30:16PM +0800, Jason Wang wrote: > > > On 2019/10/22 下午5:52, Tiwei Bie wrote: > > > > This patch introduces a mdev based hardware vhost backend. > > > > This backend is built on top of the same abstraction used > > > > in virtio-mdev and provides a generic vhost interface for > > > > userspace to accelerate the virtio devices in guest. > > > > > > > > This backend is implemented as a mdev device driver on top > > > > of the same mdev device ops used in virtio-mdev but using > > > > a different mdev class id, and it will register the device > > > > as a VFIO device for userspace to use. Userspace can setup > > > > the IOMMU with the existing VFIO container/group APIs and > > > > then get the device fd with the device name. After getting > > > > the device fd of this device, userspace can use vhost ioctls > > > > to setup the backend. > > > > > > > > Signed-off-by: Tiwei Bie <tiwei.bie@xxxxxxxxx> > > > > --- > > > > This patch depends on below series: > > > > https://lkml.org/lkml/2019/10/17/286 > > > > > > > > v1 -> v2: > > > > - Replace _SET_STATE with _SET_STATUS (MST); > > > > - Check status bits at each step (MST); > > > > - Report the max ring size and max number of queues (MST); > > > > - Add missing MODULE_DEVICE_TABLE (Jason); > > > > - Only support the network backend w/o multiqueue for now; > > > > > > Any idea on how to extend it to support devices other than net? I think we > > > want a generic API or an API that could be made generic in the future. > > > > > > Do we want to e.g having a generic vhost mdev for all kinds of devices or > > > introducing e.g vhost-net-mdev and vhost-scsi-mdev? > > One possible way is to do what vhost-user does. I.e. Apart from > > the generic ring, features, ... related ioctls, we also introduce > > device specific ioctls when we need them. As vhost-mdev just needs > > to forward configs between parent and userspace and even won't > > cache any info when possible, > > > So it looks to me this is only possible if we expose e.g set_config and > get_config to userspace. The set_config and get_config interface isn't really everything of device specific settings. We also have ctrlq in virtio-net. > > > > I think it might be better to do > > this in one generic vhost-mdev module. > > > Looking at definitions of VhostUserRequest in qemu, it mixed generic API > with device specific API. If we want go this ways (a generic vhost-mdev), > more questions needs to be answered: > > 1) How could userspace know which type of vhost it would use? Do we need to > expose virtio subsystem device in for userspace this case? > > 2) That generic vhost-mdev module still need to filter out unsupported > ioctls for a specific type. E.g if it probes a net device, it should refuse > API for other type. This in fact a vhost-mdev-net but just not modularize it > on top of vhost-mdev. > > > > > > > > > > > - Some minor fixes and improvements; > > > > - Rebase on top of virtio-mdev series v4; [...] > > > > + > > > > +static long vhost_mdev_get_features(struct vhost_mdev *m, u64 __user *featurep) > > > > +{ > > > > + if (copy_to_user(featurep, &m->features, sizeof(m->features))) > > > > + return -EFAULT; > > > > > > As discussed in previous version do we need to filter out MQ feature here? > > I think it's more straightforward to let the parent drivers to > > filter out the unsupported features. Otherwise it would be tricky > > when we want to add more features in vhost-mdev module, > > > It's as simple as remove the feature from blacklist? It's not really that easy. It may break the old drivers. > > > > i.e. if > > the parent drivers may expose unsupported features and relay on > > vhost-mdev to filter them out, these features will be exposed > > to userspace automatically when they are enabled in vhost-mdev > > in the future. > > > The issue is, it's only that vhost-mdev knows its own limitation. E.g in > this patch, vhost-mdev only implements a subset of transport API, but parent > doesn't know about that. > > Still MQ as an example, there's no way (or no need) for parent to know that > vhost-mdev does not support MQ. The mdev is a MDEV_CLASS_ID_VHOST mdev device. When the parent is being developed, it should know the currently supported features of vhost-mdev. > And this allows old kenrel to work with new > parent drivers. The new drivers should provide things like VIRTIO_MDEV_F_VERSION_1 to be compatible with the old kernels. When VIRTIO_MDEV_F_VERSION_1 is provided/negotiated, the behaviours should be consistent. > > So basically we have three choices here: > > 1) Implement what vhost-user did and implement a generic vhost-mdev (but may > still have lots of device specific code). To support advanced feature which > requires the access to config, still lots of API that needs to be added. > > 2) Implement what vhost-kernel did, have a generic vhost-mdev driver and a > vhost bus on top for match a device specific API e.g vhost-mdev-net. We > still have device specific API but limit them only to device specific > module. Still require new ioctls for advanced feature like MQ. > > 3) Simply expose all virtio-mdev transport to userspace. Currently, virtio-mdev transport is a set of function callbacks defined in kernel. How to simply expose virtio-mdev transport to userspace? > A generic module > without any type specific code (like virtio-mdev). No need dedicated API for > e.g MQ. But then the API will look much different than current vhost did. > > Consider the limitation of 1) I tend to choose 2 or 3. What's you opinion? > >
