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Date:   Wed, 4 Nov 2020 15:29:16 -0400
From:   Jason Gunthorpe <jgg@nvidia.com>
To:     "joro@8bytes.org" <joro@8bytes.org>
CC:     "Tian, Kevin" <kevin.tian@intel.com>,
        Jason Wang <jasowang@redhat.com>,
        "Liu, Yi L" <yi.l.liu@intel.com>,
        "alex.williamson@redhat.com" <alex.williamson@redhat.com>,
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Subject: Re: (proposal) RE: [PATCH v7 00/16] vfio: expose virtual Shared
 Virtual Addressing to VMs
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On Tue, Nov 03, 2020 at 08:14:29PM +0100, joro@8bytes.org wrote:
> On Tue, Nov 03, 2020 at 01:48:51PM -0400, Jason Gunthorpe wrote:
> > I think the same PCI driver with a small flag to support the PF or
> > VF is not the same as two completely different drivers in different
> > subsystems
> 
> There are counter-examples: ixgbe vs. ixgbevf.
>
> Note that also a single driver can support both, an SVA device and an
> mdev device, sharing code for accessing parts of the device like queues
> and handling interrupts.

Needing a mdev device at all is the larger issue, mdev means the
kernel must carry a lot of emulation code depending on how the SVA
device is designed. Eg creating queues may require an emulated BAR.

Shifting that code to userspace and having a single clean 'SVA'
interface from the kernel for the device makes a lot more sense,
esepcially from a security perspective.

Forcing all vIOMMU stuff to only use VFIO permanently closes this as
an option.

Jason