On Fri, 14 Feb 2020 15:57:04 +1100 Alexey Kardashevskiy <aik@xxxxxxxxx> wrote: > 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, TBH, I'm starting with the premise that a userspace PF driver already works. The DPDK folks have produced some "interesting" code that allows SR-IOV to be enabled on a PF underneath vfio-pci. There's also a non-upstream igb-uio driver associated with DPDK that seems to be recommended for SR-IOV PF driver use cases, particularly for an FPGA device. The testing I've done, and what's provided by the QEMU patch I reference, is really only unit testing the vf_token support and DEVICE_FEATURE ioctl provided here. I used this with an Intel 82576 (igb) where the PF driver doesn't particularly like being assigned to a VM with SR-IOV enabled. Likewise, I can prove that the interfaces here provide the correct restrictions for the VF, but the VF doesn't work in a VM due to the state of the PF. I'm hoping we'll have some confirmation from the DPDK folks that this provides what they need to abandon the non-upstream drivers and more nefarious hacks. There's a lot more virtualization work to be done in QEMU before I'd propose patch I reference above upstream. To your specific question regarding CX5, I think there are very few SR-IOV devices where the PF doesn't act as some kind of packet router or ring management engine. The Amazon device listed in the pci-pf-stub driver seems to be one of the few SR-IOV devices which claim the PF has no special interfaces other than exposing the SR-IOV capability itself. So I think we generally expect a device specific SR-IOV aware driver running on the PF via this interface. That's certainly the case for the DPDK code for the FPGA device above. Thanks, Alex
