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From:   "Tian, Kevin" <kevin.tian@intel.com>
To:     Alex Williamson <alex.williamson@redhat.com>
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Subject: RE: [PATCH RFC v2 00/18] Add VFIO mediated device support and DEV-MSI
 support for the idxd driver
Thread-Topic: [PATCH RFC v2 00/18] Add VFIO mediated device support and
 DEV-MSI support for the idxd driver
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Date:   Wed, 12 Aug 2020 03:35:39 +0000
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> From: Alex Williamson <alex.williamson@redhat.com>
> Sent: Wednesday, August 12, 2020 10:36 AM
> On Wed, 12 Aug 2020 01:58:00 +0000
> "Tian, Kevin" <kevin.tian@intel.com> wrote:
>=20
> > >
> > > I'll also remind folks that LPC is coming up in just a couple short
> > > weeks and this might be something we should discuss (virtually)
> > > in-person.  uconf CfPs are currently open. </plug>   Thanks,
> > >
> >
> > Yes, LPC is a good place to reach consensus. btw I saw there is
> > already one VFIO topic called "device assignment/sub-assignment".
> > Do you think whether this can be covered under that topic, or
> > makes more sense to be a new one?
>=20
> All the things listed in the CFP are only potential topics to get ideas
> flowing, there is currently no proposal to talk about sub-assignment.
> I'd suggest submitting separate topics for each and if we run into time
> constraints we can ask that they might be combined together.  Thanks,
>=20

Done.
--
title: Criteria of using VFIO mdev (vs. userspace DMA)

Content:
VFIO mdev provides a framework for subdevice assignment and reuses=20
existing VFIO uAPI  to handle common passthrough-related requirements.=20
However, subdevice (e.g. ADI defined in Intel Scalable IOV) might not be=20
a PCI endpoint (e.g. just a work queue), thus requires some degree of=20
emulation/mediation in kernel to fit into VFIO device API. Then there is=20
a concern on putting emulation in kernel and how to judge abuse of=20
mdev framework by simply using it as an easy path to hook into=20
virtualization stack. An associated open is about differentiating mdev=20
from userspace DMA framework (such as uacce), and whether building=20
passthrough features on top of userspace DMA framework is a better=20
choice than using mdev.=20

Thanks
Kevin