linux-kernel - Re: [PATCH v4 11/12] samples: add vfio-mdev-pci driver

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Date:   Thu, 16 Jan 2020 18:40:27 +0100
From:   Cornelia Huck <cohuck@...hat.com>
To:     "Liu, Yi L" <yi.l.liu@...el.com>
Cc:     "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "kwankhede@...dia.com" <kwankhede@...dia.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "peterx@...hat.com" <peterx@...hat.com>,
        "baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>
Subject: Re: [PATCH v4 11/12] samples: add vfio-mdev-pci driver

On Thu, 16 Jan 2020 13:23:28 +0000
"Liu, Yi L" <yi.l.liu@...el.com> wrote:

> > From: Cornelia Huck [mailto:cohuck@...hat.com]
> > Sent: Wednesday, January 15, 2020 8:30 PM
> > To: Liu, Yi L <yi.l.liu@...el.com>
> > Subject: Re: [PATCH v4 11/12] samples: add vfio-mdev-pci driver
> > 
> > On Tue,  7 Jan 2020 20:01:48 +0800
> > Liu Yi L <yi.l.liu@...el.com> wrote:

> > > diff --git a/samples/Kconfig b/samples/Kconfig
> > > index 9d236c3..50d207c 100644
> > > --- a/samples/Kconfig
> > > +++ b/samples/Kconfig
> > > @@ -190,5 +190,15 @@ config SAMPLE_INTEL_MEI
> > >  	help
> > >  	  Build a sample program to work with mei device.
> > >
> > > +config SAMPLE_VFIO_MDEV_PCI
> > > +	tristate "Sample driver for wrapping PCI device as a mdev"
> > > +	select VFIO_PCI_COMMON
> > > +	select VFIO_PCI  
> > 
> > Why does this still need to select VFIO_PCI? Shouldn't all needed
> > infrastructure rather be covered by VFIO_PCI_COMMON already?  
> 
> VFIO_PCI_COMMON is supposed to be the dependency of both VFIO_PCI and
> SAMPLE_VFIO_MDEV_PCI. However, the source code of VFIO_PCI_COMMON are
> under drivers/vfio/pci which is compiled per the configuration of VFIO_PCI.
> Besides of letting SAMPLE_VFIO_MDEV_PCI select VFIO_PCI, I can also add
> a line in drivers/vfio/Makefile to make the source code under drivers/vfio/pci
> to be compiled when either VFIO_PCI or VFIO_PCI_COMMON are configed. But
> I'm afraid it is a bit ugly. So I choose to let SAMPLE_VFIO_MDEV_PCI select
> VFIO_PCI. If you have other idea, I would be pleased to
> know it. :-)

Shouldn't building drivers/vfio/pci/ for CONFIG_VFIO_PCI_COMMON already
be enough (the Makefile changes look fine to me)? Or am I missing
something obvious?

> 
> >   
> > > +	depends on VFIO_MDEV && VFIO_MDEV_DEVICE  
> > 
> > VFIO_MDEV_DEVICE already depends on VFIO_MDEV. But maybe also make this
> > depend on PCI?
> >   
> > > +	help
> > > +	  Sample driver for wrapping a PCI device as a mdev. Once bound to
> > > +	  this driver, device passthru should through mdev path.  
> > 
> > "A PCI device bound to this driver will be assigned through the
> > mediated device framework."
> > 
> > ?  
> 
> Maybe I should have mentioned it as "A PCI device bound to this
> sample driver should follow the passthru steps for mdevs as showed
> in Documentation/driver-api/vfio-mediated-device.rst."
> 
> Does it make more sense?

Yes, it does :)