[PATCH v2 0/7] vfio/pci: SR-IOV support

Alex Williamson
2020-02-19T18:54:04Z

Changes since v1 are primarily to patch 3/7 where the commit log is
rewritten, along with option parsing and failure logging based on
upstream discussions. The primary user visible difference is that
option parsing is now much more strict. If a vf_token option is
provided that cannot be used, we generate an error. As a result of
this, opening a PF with a vf_token option will serve as a mechanism of
setting the vf_token. This seems like a more user friendly API than
the alternative of sometimes requiring the option (VFs in use) and
sometimes rejecting it, and upholds our desire that the option is
always either used or rejected.

This also means that the VFIO_DEVICE_FEATURE ioctl is not the only
means of setting the VF token, which might call into question whether
we absolutely need this new ioctl. Currently I'm keeping it because I
can imagine use cases, for example if a hypervisor were to support
SR-IOV, the PF device might be opened without consideration for a VF
token and we'd require the hypservisor to close and re-open the PF in
order to set a known VF token, which is impractical.

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

RFC: https://lore.kernel.org/lkml/158085337582.9445.17682266437583505502.stgit@gimli.home/
v1: https://lore.kernel.org/lkml/158145472604.16827.15751375540102298130.stgit@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 | 383 +++++++++++++++++++++++++++++++++--
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, 426 insertions(+), 28 deletions(-)