Re: [Qemu-devel] [RFC v6-based v1 0/5] refine mdev framework

[Dong Jia]

On Tue, 16 Aug 2016 16:14:12 +0800
Jike Song <address@hidden> wrote:

> 
> This patchset is based on NVidia's "Add Mediated device support" series, 
> version 6:
> 
>       http://www.spinics.net/lists/kvm/msg136472.html
> 
> 
> Background:
> 
>       The patchset from NVidia introduced the Mediated Device support to
>       Linux/VFIO. With that series, one can create virtual devices (supporting
>       by underlying physical device and vendor driver), and assign them to
>       userspace like QEMU/KVM, in the same way as device assignment via VFIO.
> 
>       Based on that, NVidia and Intel implemented their vGPU solutions, IBM
>       implemented its CCW pass-through.  However, there are limitations
>       imposed by current (v6 in particular) mdev framework: the mdev must be
>       represented as a PCI device, several vfio capabilities such as
>       sparse mmap are not possible, and so forth.
> 
>       This series aims to address above limitations and simplify the 
> implementation.
> 
> 
> Key Changes:
> 
>       - An independent "struct device" was introduced to parent_device, thus
>         a hierarchy in driver core is formed with physical device, parent 
> device
>         and mdev device;
> 
>       - Leveraging the mechanism and APIs provided by Linux driver core, it
>         is now safe to remove all refcnts and locks;
> 
>       - vfio_mpci (later renamed to vfio_mdev) was made BUS-agnostic: all
>         PCI-specific logic was removed, accesses from userspace are now
>         passed to vendor driver directly, thus guaranteed that full VFIO
>         capabilities provided: e.g. dynamic regions, sparse mmap, etc.;
> 
>         With vfio_mdev being BUS-agnostic, it is enough to have only one
>         driver for all mdev devices;

Hi Jike:

I don't know what happened, but finding out which direction this will
likely go seems my first priority now...

I'd say, either with only the original mdev v6, or patched this series,
vfio-ccw could live. But this series saves my work of mimicing the
vfio-mpci code in my vfio-mccw driver. I like this incremental patches.

I'm wondering if Alex and the Nvidia folks have some comments for this
from their point of views. And I'm really looking forward on their
feedback.

Thanks!

> 
>       - UUID was removed from the interface between mdev and vendor driver;
> 
> 
> TODO
> 
>       remove mdev stuff from vfio.h
>       update doc
> 


--------
Dong Jia