Re: [PATCH v3 0/7] vfio/pci: SR-IOV support

[Alex Williamson <alex.williamson@redhat.com>]

On Thu, 19 Mar 2020 06:32:25 +0000
"Tian, Kevin" <kevin.tian@intel.com> wrote:

> > From: Alex Williamson <alex.williamson@redhat.com>
> > Sent: Thursday, March 12, 2020 5:58 AM
> > 
> > Only minor tweaks since v2, GET and SET on VFIO_DEVICE_FEATURE are
> > enforced mutually exclusive except with the PROBE option as suggested
> > by Connie, the modinfo text has been expanded for the opt-in to enable
> > SR-IOV support in the vfio-pci driver per discussion with Kevin.
> > 
> > I have not incorporated runtime warnings attempting to detect misuse
> > of SR-IOV or imposed a session lifetime of a VF token, both of which
> > were significant portions of the discussion of the v2 series.  Both of
> > these also seem to impose a usage model or make assumptions about VF
> > resource usage or configuration requirements that don't seem necessary
> > except for the sake of generating a warning or requiring an otherwise
> > unnecessary and implicit token reinitialization.  If there are new
> > thoughts around these or other discussion points, please raise them.
> > 
> > Series overview (same as provided with v1):
> > 
> > The synopsis of this series is that we have an ongoing desire to drive
> > PCIe SR-IOV PFs from userspace with VFIO.  There's an immediate need
> > for this with DPDK drivers and potentially interesting future use
> > cases in virtualization.  We've been reluctant to add this support
> > previously due to the dependency and trust relationship between the
> > VF device and PF driver.  Minimally the PF driver can induce a denial
> > of service to the VF, but depending on the specific implementation,
> > the PF driver might also be responsible for moving data between VFs
> > or have direct access to the state of the VF, including data or state
> > otherwise private to the VF or VF driver.
> > 
> > To help resolve these concerns, we introduce a VF token into the VFIO
> > PCI ABI, which acts as a shared secret key between drivers.  The
> > userspace PF driver is required to set the VF token to a known value
> > and userspace VF drivers are required to provide the token to access
> > the VF device.  If a PF driver is restarted with VF drivers in use, it
> > must also provide the current token in order to prevent a rogue
> > untrusted PF driver from replacing a known driver.  The degree to
> > which this new token is considered secret is left to the userspace
> > drivers, the kernel intentionally provides no means to retrieve the
> > current token.
> > 
> > Note that the above token is only required for this new model where
> > both the PF and VF devices are usable through vfio-pci.  Existing
> > models of VFIO drivers where the PF is used without SR-IOV enabled
> > or the VF is bound to a userspace driver with an in-kernel, host PF
> > driver are unaffected.
> > 
> > The latter configuration above also highlights a new inverted scenario
> > that is now possible, a userspace PF driver with in-kernel VF drivers.
> > I believe this is a scenario that should be allowed, but should not be
> > enabled by default.  This series includes code to set a default
> > driver_override for VFs sourced from a vfio-pci user owned PF, such
> > that the VFs are also bound to vfio-pci.  This model is compatible
> > with tools like driverctl and allows the system administrator to
> > decide if other bindings should be enabled.  The VF token interface
> > above exists only between vfio-pci PF and VF drivers, once a VF is
> > bound to another driver, the administrator has effectively pronounced
> > the device as trusted.  The vfio-pci driver will note alternate
> > binding in dmesg for logging and debugging purposes.
> > 
> > Please review, comment, and test.  The example QEMU implementation
> > provided with the RFC is still current for this version.  Thanks,
> > 
> > Alex  
> 
> The whole series looks good to me:
> 	Reviewed-by: Kevin Tian <kevin.tian@intel.com>

Thanks!

> and confirm one understanding here, since it is not discussed anywhere. For
> VM live migration with assigned VF device, it is not necessary to migrate the
> VF token itself and actually we don't allow userspace to retrieve it. Instead,
> Qemu just follows whatever token requirement on the dest to open the new
> VF: could be same or different token as/from src, or even no token if PF
> driver runs in kernel on dest. I suppose either combination could work, correct?

That's correct.  Thanks,

Alex

> > RFC:
> > https://lore.kernel.org/lkml/158085337582.9445.17682266437583505502.stg
> > it@gimli.home/
> > v1:
> > https://lore.kernel.org/lkml/158145472604.16827.15751375540102298130.st
> > git@gimli.home/
> > v2:
> > https://lore.kernel.org/lkml/158213716959.17090.8399427017403507114.stg
> > it@gimli.home/
> > 
> > ---
> > 
> > Alex Williamson (7):
> >       vfio: Include optional device match in vfio_device_ops callbacks
> >       vfio/pci: Implement match ops
> >       vfio/pci: Introduce VF token
> >       vfio: Introduce VFIO_DEVICE_FEATURE ioctl and first user
> >       vfio/pci: Add sriov_configure support
> >       vfio/pci: Remove dev_fmt definition
> >       vfio/pci: Cleanup .probe() exit paths
> > 
> > 
> >  drivers/vfio/pci/vfio_pci.c         |  390
> > +++++++++++++++++++++++++++++++++--
> >  drivers/vfio/pci/vfio_pci_private.h |   10 +
> >  drivers/vfio/vfio.c                 |   20 +-
> >  include/linux/vfio.h                |    4
> >  include/uapi/linux/vfio.h           |   37 +++
> >  5 files changed, 433 insertions(+), 28 deletions(-)  
>