On Fri, 6 Mar 2020 09:45:40 +0000 "Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote: > > From: Tian, Kevin > > Sent: Friday, March 6, 2020 3:57 PM > > > > > From: Alex Williamson <alex.williamson@xxxxxxxxxx> > > > Sent: Friday, March 6, 2020 2:23 AM > > > > > > On Tue, 25 Feb 2020 03:08:00 +0000 > > > "Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote: > > > > > > > > From: Alex Williamson > > > > > Sent: Thursday, February 20, 2020 2:54 AM > > > > > > > > > > With the VF Token interface we can now expect that a vfio userspace > > > > > driver must be in collaboration with the PF driver, an unwitting > > > > > userspace driver will not be able to get past the GET_DEVICE_FD step > > > > > in accessing the device. We can now move on to actually allowing > > > > > SR-IOV to be enabled by vfio-pci on the PF. Support for this is not > > > > > enabled by default in this commit, but it does provide a module option > > > > > for this to be enabled (enable_sriov=1). Enabling VFs is rather > > > > > straightforward, except we don't want to risk that a VF might get > > > > > autoprobed and bound to other drivers, so a bus notifier is used to > > > > > "capture" VFs to vfio-pci using the driver_override support. We > > > > > assume any later action to bind the device to other drivers is > > > > > condoned by the system admin and allow it with a log warning. > > > > > > > > > > vfio-pci will disable SR-IOV on a PF before releasing the device, > > > > > allowing a VF driver to be assured other drivers cannot take over the > > > > > PF and that any other userspace driver must know the shared VF token. > > > > > This support also does not provide a mechanism for the PF userspace > > > > > driver itself to manipulate SR-IOV through the vfio API. With this > > > > > patch SR-IOV can only be enabled via the host sysfs interface and the > > > > > PF driver user cannot create or remove VFs. > > > > > > > > I'm not sure how many devices can be properly configured simply > > > > with pci_enable_sriov. It is not unusual to require PF driver prepare > > > > something before turning PCI SR-IOV capability. If you look kernel > > > > PF drivers, there are only two using generic pci_sriov_configure_ > > > > simple (simple wrapper like pci_enable_sriov), while most others > > > > implementing their own callback. However vfio itself has no idea > > > > thus I'm not sure how an user knows whether using this option can > > > > actually meet his purpose. I may miss something here, possibly > > > > using DPDK as an example will make it clearer. > > > > > > There is still the entire vfio userspace driver interface. Imagine for > > > example that QEMU emulates the SR-IOV capability and makes a call out > > > to libvirt (or maybe runs with privs for the PF SR-IOV sysfs attribs) > > > when the guest enables SR-IOV. Can't we assume that any PF specific > > > support can still be performed in the userspace/guest driver, leaving > > > us with a very simple and generic sriov_configure callback in vfio-pci? > > > > Makes sense. One concern, though, is how an user could be warned > > if he inadvertently uses sysfs to enable SR-IOV on a vfio device whose > > userspace driver is incapable of handling it. Note any VFIO device, > > if SR-IOV capable, will allow user to do so once the module option is > > turned on and the callback is registered. I felt such uncertainty can be > > contained by toggling SR-IOV through a vfio api, but from your description > > obviously it is what you want to avoid. Is it due to the sequence reason, > > e.g. that SR-IOV must be enabled before userspace PF driver sets the > > token? > > > > reading again I found that you specifically mentioned "the PF driver user > cannot create or remove VFs.". However I failed to get the rationale > behind. If the VF drivers have built the trust with the PF driver through > the token, what is the problem of allowing the PF driver to further manage > SR-IOV itself? suppose any VF removal will be done in a cooperate way > to avoid surprise impact to related VF drivers. then possibly a new vfio > ioctl for setting the VF numbers plus a token from the userspace driver > could also serve the purpose of this patch series (GET_DEVICE_FD + sysfs)? If a user is allowed to create VFs, does that user automatically get ownership of those devices? How is that accomplished? What if we want to make use of the VF via a separate process? How do we coordinate that with the PF driver? All of these problems are resolved if we assume the userspace PF driver needs to operate in collaboration with a privileged entity to interact with sysfs to configure SR-IOV and manage the resulting VFs. I have no desire to take on that responsibility within vfio-pci and I also feel that a user owning a PF device should not inherently grant that user the ability to create and remove other devices on the host, even if they are sourced from the PF. Thanks, Alex
