On Tue, 19 Jul 2016 09:10:17 -0600 Alex Williamson <alex.williamson@xxxxxxxxxx> wrote: > On Tue, 19 Jul 2016 07:06:34 +0000 > "Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote: > > > > From: Alex Williamson > > > Sent: Tuesday, July 19, 2016 5:34 AM > > > > > > On Sun, 17 Jul 2016 13:05:21 +0300 > > > Haggai Eran <haggaie@xxxxxxxxxxxx> wrote: > > > > > > > On 7/14/2016 8:03 PM, Alex Williamson wrote: > > > > >> 2. Add an owner_pid to struct vfio_group and make sure in > > > vfio_group_get_device_fd that > > > > >> > the PFs vfio_group is owned by the same process as the one that is trying to get > > > a fd for a VF. > > > > > This only solves a very specific use case, it doesn't address any of > > > > > the issues where the VF struct device in the host kernel might get > > > > > bound to another driver. > > > > The current patch uses driver_override to make the kernel use VFIO for > > > > all the new VFs. It still allows the host kernel to bind them to another > > > > driver, but that would require an explicit action on the part of the > > > > administrator. Don't you think that is enough? > > > > > > Binding the VFs to vfio-pci with driver_override just prevents any sort > > > of initial use by native host drivers, it doesn't in any way tie them to > > > the user that created them or prevent any normal operations on the > > > device. The entire concept of a user-created device is new and > > > entirely separate from a user-owned device as typically used with > > > vfio. We currently have an assumption with VF assignment that the PF > > > is trusted in the host, that's broken here and I have a hard time > > > blaming it on the admin or management tool for allowing such a thing > > > when it previously hasn't been a possibility. If nothing else, it > > > seems like we're opening the system for phishing attempts where a user > > > of a PF creates VFs hoping they might be assigned to a victim VM, or > > > worse the host. > > > > > > > What about fully virtualizing the SR-IOV capability? The VM is not allowed > > to touch physical SR-IOV capability directly so there would not be a problem > > of user-created devices. Physical SR-IOV is always enabled by admin at > > the host side. Admin can combine any number of VFs (even cross multiple > > compatible devices) in the virtual SR-IOV capability on any passthrough > > device... > > > > The limitation is that the VM can initially access only PF resource which is > > usually less than what the entire device provides, so not that efficient > > when the VM doesn't want to enable SR-IOV at all. > > Are you suggesting a scenario where we have one PF with SR-IOV disabled > assigned to the user and another PF owned by the host with SR-IOV > enable, we virtualize SR-IOV to the user and use the VFs from the other > PF to act as a "pool" of VFs to be exposed to the user depending on > SR-IOV manipulation? Something like that could work with existing > vfio, just requiring the QEMU bits to virtualize SR-IOV and mange the > VFs, but I expect it's not a useful model for Mellanox. I believe it > was Ilya that stated the purpose in exposing SR-IOV was for > development, so I'm assuming they actually want to do development of > the PF SR-IOV enabling in a VM, not just give the illusion of SR-IOV to > the VM. Thanks, Thinking about this further, it seems that trying to create this IOV enablement interface through a channel which is explicitly designed to interact with an untrusted and potentially malicious user is the wrong approach. We already have an interface for a trusted entity to enable VFs, it's through pci-sysfs. Therefore if we were to use something like libvirt to orchestrate the lifecycle of the VFs, I think we remove a lot of the problems. In this case QEMU would virtualize the SR-IOV capability (maybe this is along the lines of what Kevin was thinking), but that virtualization would take a path out through the QEMU QMP interface to execute the SR-IOV change on the device rather than going through the vfio kernel interface. A management tool like libvirt would then need to translate that into sysfs operations to create the VFs and do whatever we're going to do with them (device_add them back to the VM, make them available to a peer VM, make them available to the host *gasp*). VFIO in the kernel would need to add SR-IOV support, but the only automatic SR-IOV path would be to disable IOV when the PF is released, enabling would only occur through sysfs. We would probably need a new pci-sysfs interface to manage the driver for newly created VFs though to avoid default host drivers (sriov_driver_override?). In this model QEMU is essentially just making requests to other userspace entities to perform actions and how those actions are performed can be left to userspace policy, not kernel policy. I think this would still satisfy the development use case, the enabling path just takes a different route where privileged userspace is more intimately involved in the process. Thoughts? Thanks, Alex -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
