linux-kernel - Re: [RFC v1 0/2] vfio/pci: wrap pci device as mdev with vfio-pci driver

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Date:   Thu, 7 Mar 2019 13:39:31 -0700
From:   Alex Williamson <alex.williamson@...hat.com>
To:     "Liu, Yi L" <yi.l.liu@...el.com>
Cc:     kwankhede@...dia.com, kevin.tian@...el.com,
        baolu.lu@...ux.intel.com, joro@...tes.org,
        jean-philippe.brucker@....com, peterx@...hat.com,
        linux-kernel@...r.kernel.org, yi.y.sun@...el.com
Subject: Re: [RFC v1 0/2] vfio/pci: wrap pci device as mdev with vfio-pci
 driver

On Sun,  3 Mar 2019 20:57:59 +0800
"Liu, Yi L" <yi.l.liu@...el.com> wrote:

> This patchset aims to add a vfio-pci-like meta driver on existing
> PCI devices, as a demo user of the vfio changes introduced in
> "vfio/mdev: IOMMU aware mediated device" patchset from Baolu Lu.
> 
> To build such a meta driver. We have two choices.
> a) add a vfio-pci alike sample driver under samples directory
> b) add some extensions in vfio-pci driver to make it wrap pci
>    device as mdev
> 
> For choice a), the new sample driver will have quite a few
> duplicated code with vfio-pci driver since the new sample
> driver also wants to virtualize the PCI config space. So
> this choice may bring in extra maintain effort in kernel
> and also looks strange since there will be a bunch of
> duplicated code with vfio-pci driver.
> 
> For choice b), it may reuse the existing vfio-pci driver
> by adding a new working mode. With this mode, user can wrap
> a pci device as a mediated device by binding it with the
> vfio-pci driver which works in the new mode. Thus can be used
> to verify the ""vfio/mdev: IOMMU aware mediated device"
> patchset.
> 
> This patchset is following choice b). However, we are open on
> the direction of the implementation of this vfio-pci-like meta
> driver. Pls feel free give your suggestions.

Thanks for doing this Yi!  Rather than a module option for vfio-pci,
what about having this build into a separate module (ex.
vfio-pci-mdev)?  Then we could test "regular" vfio-pci along side mdev
wrapped devices simply by which driver we bind and it'd probably be more
friendly to existing users, like libvirt.  This might also make a good
base driver for experimenting with device specific mdev migration as
well.  Thanks,

Alex