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

[Alexey Kardashevskiy <aik@ozlabs.ru>]

On 12/02/2020 10:05, Alex Williamson wrote:
> Given the mostly positive feedback from the RFC[1], here's a new
> non-RFC revision.  Changes since RFC:
> 
>  - vfio_device_ops.match semantics refined
>  - Use helpers for struct pci_dev.physfn to avoid breakage without
>    CONFIG_PCI_IOV
>  - Relax to allow SR-IOV configuration changes while PF is opened.
>    There are potentially interesting use cases here, including
>    perhaps QEMU emulating an SR-IOV capability and calling out
>    to a privileged entity to manipulate sriov_numvfs and corral
>    the resulting devices.
>  - Retest vfio_device_feature.argsz to include uuid length.
>  - Add Connie's R-b on 6/7
> 
> I still wish we had a solution to make it less opaque to the user
> why a VFIO_GROUP_GET_DEVICE_FD() has failed if a VF token is
> required, but this is still the best I've been able to come up with.
> If there are objections or better ideas, please raise them now.
> 
> 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[2] is still current for this version.  Thanks,


It is a cool feature. One question - what device have you tested it with?

Does not a PF want to control/manage VFs on a PF driver side? I am
thinking of Mellanox CX5 or similar NIC and it acts as an managed
ethernet switch which might want to do something to VFs and VFs may not
work as expected without PF's native driver doing things to it, or this
is not a concern, is it? Thanks,


> 
> Alex
> 
> [1] https://lore.kernel.org/lkml/158085337582.9445.17682266437583505502.stgit@gimli.home/
> [2] https://lore.kernel.org/lkml/20200204161737.34696b91@w520.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         |  312 ++++++++++++++++++++++++++++++++---
>  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, 355 insertions(+), 28 deletions(-)
> 

-- 
Alexey