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Date:   Wed, 5 Feb 2020 07:18:26 -0700
From:   Alex Williamson <alex.williamson@redhat.com>
To:     "Liu, Yi L" <yi.l.liu@intel.com>
Cc:     "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        "linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
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        "mtosatti@redhat.com" <mtosatti@redhat.com>,
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        "bluca@debian.org" <bluca@debian.org>,
        "jerinjacobk@gmail.com" <jerinjacobk@gmail.com>,
        "Richardson, Bruce" <bruce.richardson@intel.com>,
        "cohuck@redhat.com" <cohuck@redhat.com>
Subject: Re: [RFC PATCH 0/7] vfio/pci: SR-IOV support
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On Wed, 5 Feb 2020 07:57:36 +0000
"Liu, Yi L" <yi.l.liu@intel.com> wrote:

> > From: Alex Williamson <alex.williamson@redhat.com>
> > Sent: Wednesday, February 5, 2020 7:18 AM
> > To: kvm@vger.kernel.org
> > Subject: Re: [RFC PATCH 0/7] vfio/pci: SR-IOV support
> > 
> > 
> > Promised example QEMU test case...
> > 
> > commit 3557c63bcb286c71f3f7242cad632edd9e297d26
> > Author: Alex Williamson <alex.williamson@redhat.com>
> > Date:   Tue Feb 4 13:47:41 2020 -0700
> > 
> >     vfio-pci: QEMU support for vfio-pci VF tokens
> > 
> >     Example support for using a vf_token to gain access to a device as
> >     well as using the VFIO_DEVICE_FEATURE interface to set the VF token.
> >     Note that the kernel will disregard the additional option where it's
> >     not required, such as opening the PF with no VF users, so we can
> >     always provide it.
> > 
> >     NB. It's unclear whether there's value to this QEMU support without
> >     further exposure of SR-IOV within a VM.  This is meant mostly as a
> >     test case where the real initial users will likely be DPDK drivers.
> > 
> >     Signed-off-by: Alex Williamson <alex.williamson@redhat.com>  
> 
> Just curious how UUID is used across the test. Should the QEMU
> which opens VFs add the vfio_token=UUID or the QEMU which
> opens PF add the vfio_token=UUID? or both should add vfio_token=UUID.

In this example we do both as this covers the case where there are
existing VF users, which requires the PF to also provide the vf_token.
If there are no VF users, the PF is not required to provide a vf_token
and vfio-pci will not fail the device match if a vf_token is provided
but not needed.  In fact, when a PF is probed by vfio-pci a random
vf_token is set, so it's required to use a PF driver to set a known
vf_token before any VF users can access their VFs.  Thanks,

Alex