Re: [PATCH v6 00/20] Add VFIO mediated device support and DEV-MSI support for the idxd driver

[Dave Jiang]

On 6/7/2021 12:11 PM, Jason Gunthorpe wrote:
> On Mon, Jun 07, 2021 at 11:13:04AM -0700, Dave Jiang wrote:
>
> > So in step 1, we 'tag' the wq to be dedicated to guest usage and put the
> > hardware wq into enable state. For a dedicated mode wq, we can definitely
> > just register directly and skip the mdev step. For a shared wq mode, we can
> > have multiple mdev running on top of a single wq. So we need some way to
> > create more mdevs. We can either go with the existing established creation
> > path by mdev, or invent something custom for the driver as Jason suggested
> > to accomodate additional virtual devices for guests. We implemented the mdev
> > path originally with consideration of mdev is established and has a known
> > interface already.
> It sounds like you could just as easially have a 'create new vfio'
> file under the idxd sysfs.. Especially since you already have a bus
> and dynamic vfio specific things being created on this bus.

Will explore this and using of 'struct vfio_device' without mdev.



> Have you gone over this with Dan?
>
> > I think things become more complicated when we go from a dedicated wq to
> > shared wq where the relationship of wq : mdev is 1 : 1 goes to 1 : N. Also
> > needing to keep a consistent user config experience is desired, especially
> > we already have such behavior since kernel 5.6 for host usages. So we really
> > need try to avoid doing wq configuration differently just for "mdev" wqs. In
> > the case suggested above, we basically just flipped the configuration steps.
> > Mdev is first created through mdev sysfs interface. And then the device
> > paramters are configured. Where for us, we configure the device parameter
> > first, and then create the mdev. But in the end, it's still the hybrid mdev
> > setup right?
> So you don't even use mdev to configure anything? Yuk.
>
> Jason