linux-kernel - Re: [PATCH V3 0/7] mdev based hardware virtio offloading support

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Date:   Tue, 15 Oct 2019 15:37:20 +0100
From:   Stefan Hajnoczi <stefanha@...il.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     kvm@...r.kernel.org, linux-s390@...r.kernel.org,
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Subject: Re: [PATCH V3 0/7] mdev based hardware virtio offloading support

On Tue, Oct 15, 2019 at 11:37:17AM +0800, Jason Wang wrote:
> 
> On 2019/10/15 上午1:49, Stefan Hajnoczi wrote:
> > On Fri, Oct 11, 2019 at 04:15:50PM +0800, Jason Wang wrote:
> > > There are hardware that can do virtio datapath offloading while having
> > > its own control path. This path tries to implement a mdev based
> > > unified API to support using kernel virtio driver to drive those
> > > devices. This is done by introducing a new mdev transport for virtio
> > > (virtio_mdev) and register itself as a new kind of mdev driver. Then
> > > it provides a unified way for kernel virtio driver to talk with mdev
> > > device implementation.
> > > 
> > > Though the series only contains kernel driver support, the goal is to
> > > make the transport generic enough to support userspace drivers. This
> > > means vhost-mdev[1] could be built on top as well by resuing the
> > > transport.
> > > 
> > > A sample driver is also implemented which simulate a virito-net
> > > loopback ethernet device on top of vringh + workqueue. This could be
> > > used as a reference implementation for real hardware driver.
> > > 
> > > Consider mdev framework only support VFIO device and driver right now,
> > > this series also extend it to support other types. This is done
> > > through introducing class id to the device and pairing it with
> > > id_talbe claimed by the driver. On top, this seris also decouple
> > > device specific parents ops out of the common ones.
> > I was curious so I took a quick look and posted comments.
> > 
> > I guess this driver runs inside the guest since it registers virtio
> > devices?
> 
> 
> It could run in either guest or host. But the main focus is to run in the
> host then we can use virtio drivers in containers.
> 
> 
> > 
> > If this is used with physical PCI devices that support datapath
> > offloading then how are physical devices presented to the guest without
> > SR-IOV?
> 
> 
> We will do control path meditation through vhost-mdev[1] and vhost-vfio[2].
> Then we will present a full virtio compatible ethernet device for guest.
> 
> SR-IOV is not a must, any mdev device that implements the API defined in
> patch 5 can be used by this framework.

What I'm trying to understand is: if you want to present a virtio-pci
device to the guest (e.g. using vhost-mdev or vhost-vfio), then how is
that related to this patch series?

Does this mean this patch series is useful mostly for presenting virtio
devices to containers or the host?

Stefan

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