linux-kernel - Re: [PATCH 8/9] vfio/pci: export nvlink2 support into vendor vfio

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Message-ID: <20210319162848.GZ2356281@nvidia.com>
Date:   Fri, 19 Mar 2021 13:28:48 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Christoph Hellwig <hch@....de>
Cc:     Alex Williamson <alex.williamson@...hat.com>,
        Max Gurtovoy <mgurtovoy@...dia.com>,
        Alexey Kardashevskiy <aik@...abs.ru>, cohuck@...hat.com,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        liranl@...dia.com, oren@...dia.com, tzahio@...dia.com,
        leonro@...dia.com, yarong@...dia.com, aviadye@...dia.com,
        shahafs@...dia.com, artemp@...dia.com, kwankhede@...dia.com,
        ACurrid@...dia.com, cjia@...dia.com, yishaih@...dia.com,
        mjrosato@...ux.ibm.com
Subject: Re: [PATCH 8/9] vfio/pci: export nvlink2 support into vendor
 vfio_pci drivers

On Fri, Mar 19, 2021 at 05:20:33PM +0100, Christoph Hellwig wrote:
> On Fri, Mar 19, 2021 at 01:17:22PM -0300, Jason Gunthorpe wrote:
> > I think we talked about this.. We still need a better way to control
> > binding of VFIO modules - now that we have device-specific modules we
> > must have these match tables to control what devices they connect
> > to.
> > 
> > Previously things used the binding of vfio_pci as the "switch" and
> > hardcoded all the matches inside it.
> > 
> > I'm still keen to try the "driver flavour" idea I outlined earlier,
> > but it is hard to say what will resonate with Greg.
> 
> IMHO the only model that really works and makes sense is to turn the
> whole model around and make vfio a library called by the actual driver
> for the device.  That is any device that needs device specific
> funtionality simply needs a proper in-kernel driver, which then can be
> switched to a vfio mode where all the normal subsystems are unbound
> from the device, and VFIO functionality is found to it all while _the_
> driver that controls the PCI ID is still in charge of it.

Yes, this is what I want to strive for with Greg.

It would also resolve alot of the uncomfortable code I see in VFIO
using the driver core. For instance, when a device is moved to 'vfio
mode' it can go through and *lock* the entire group of devices to
'vfio mode' or completely fail.

This would replace all the protective code that is all about ensuring
the admin doesn't improperly mix & match in-kernel and vfio drivers
within a security domain.

The wrinkle I don't yet have an easy answer to is how to load vfio_pci
as a universal "default" within the driver core lazy bind scheme and
still have working module autoloading... I'm hoping to get some
research into this..

Jason