linux-kernel - RE: [RFC PATCH 0/7] vfio/pci: SR-IOV support

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Date:   Wed, 5 Feb 2020 07:57:21 +0000
From:   "Liu, Yi L" <yi.l.liu@...el.com>
To:     Alex Williamson <alex.williamson@...hat.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>
CC:     "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "dev@...k.org" <dev@...k.org>,
        "mtosatti@...hat.com" <mtosatti@...hat.com>,
        "thomas@...jalon.net" <thomas@...jalon.net>,
        "bluca@...ian.org" <bluca@...ian.org>,
        "jerinjacobk@...il.com" <jerinjacobk@...il.com>,
        "Richardson, Bruce" <bruce.richardson@...el.com>,
        "cohuck@...hat.com" <cohuck@...hat.com>
Subject: RE: [RFC PATCH 0/7] vfio/pci: SR-IOV support

Hi Alex,

Silly questions on the background:

> From: Alex Williamson <alex.williamson@...hat.com>
> Sent: Wednesday, February 5, 2020 7:06 AM
> Subject: [RFC PATCH 0/7] vfio/pci: SR-IOV support
> 
> There seems to be an ongoing desire to use userspace, vfio-based
> drivers for both SR-IOV PF and VF devices. 

Is this series to make PF be bound-able to vfio-pci even SR-IOV is
enabled on such PFs? If yes, is it allowed to assign PF to a VM? or
it can only be used by userspace applications like DPDK?

> The fundamental issue
> with this concept is that the VF is not fully independent of the PF
> driver.  Minimally the PF driver might be able to deny service to the
> VF, VF data paths might be dependent on the state of the PF device,
> or the PF my have some degree of ability to inspect or manipulate the
> VF data.  It therefore would seem irresponsible to unleash VFs onto
> the system, managed by a user owned PF.
> 
> We address this in a few ways in this series.  First, we can use a bus
> notifier and the driver_override facility to make sure VFs are bound
> to the vfio-pci driver by default.  This should eliminate the chance
> that a VF is accidentally bound and used by host drivers.  We don't
> however remove the ability for a host admin to change this override.
> 
> The next issue we need to address is how we let userspace drivers
> opt-in to this participation with the PF driver.  We do not want an
> admin to be able to unwittingly assign one of these VFs to a tenant
> that isn't working in collaboration with the PF driver.  We could use
> IOMMU grouping, but this seems to push too far towards tightly coupled
> PF and VF drivers.  This series introduces a "VF token", implemented
> as a UUID, as a shared secret between PF and VF drivers.  The token
> needs to be set by the PF driver and used as part of the device
> matching by the VF driver.  Provisions in the code also account for
> restarting the PF driver with active VF drivers, requiring the PF to
> use the current token to re-gain access to the PF.

How about the scenario in which PF driver is vfio-based userspace
driver but VF drivers are mixed. This means not all VFs are bound
to vfio-based userspace driver. Is it also supported here? :-)

Regards,
Yi Liu