On Tue, Mar 24, 2020 at 10:49:54PM +0800, Alex Williamson wrote: > On Tue, 24 Mar 2020 09:23:31 +0000 > "Dr. David Alan Gilbert" <dgilbert@xxxxxxxxxx> wrote: > > > * Yan Zhao (yan.y.zhao@xxxxxxxxx) wrote: > > > On Tue, Mar 24, 2020 at 05:29:59AM +0800, Alex Williamson wrote: > > > > On Mon, 3 Jun 2019 20:34:22 -0400 > > > > Yan Zhao <yan.y.zhao@xxxxxxxxx> wrote: > > > > > > > > > On Tue, Jun 04, 2019 at 03:29:32AM +0800, Alex Williamson wrote: > > > > > > On Thu, 30 May 2019 20:44:38 -0400 > > > > > > Yan Zhao <yan.y.zhao@xxxxxxxxx> wrote: > > > > > > > > > > > > > This patchset introduces a migration_version attribute under sysfs of VFIO > > > > > > > Mediated devices. > > > > > > > > > > > > > > This migration_version attribute is used to check migration compatibility > > > > > > > between two mdev devices of the same mdev type. > > > > > > > > > > > > > > Patch 1 defines migration_version attribute in > > > > > > > Documentation/vfio-mediated-device.txt > > > > > > > > > > > > > > Patch 2 uses GVT as an example to show how to expose migration_version > > > > > > > attribute and check migration compatibility in vendor driver. > > > > > > > > > > > > Thanks for iterating through this, it looks like we've settled on > > > > > > something reasonable, but now what? This is one piece of the puzzle to > > > > > > supporting mdev migration, but I don't think it makes sense to commit > > > > > > this upstream on its own without also defining the remainder of how we > > > > > > actually do migration, preferably with more than one working > > > > > > implementation and at least prototyped, if not final, QEMU support. I > > > > > > hope that was the intent, and maybe it's now time to look at the next > > > > > > piece of the puzzle. Thanks, > > > > > > > > > > > > Alex > > > > > > > > > > Got it. > > > > > Also thank you and all for discussing and guiding all along:) > > > > > We'll move to the next episode now. > > > > > > > > Hi Yan, > > > > > > > > As we're hopefully moving towards a migration API, would it make sense > > > > to refresh this series at the same time? I think we're still expecting > > > > a vendor driver implementing Kirti's migration API to also implement > > > > this sysfs interface for compatibility verification. Thanks, > > > > > > > Hi Alex > > > Got it! > > > Thanks for reminding of this. And as now we have vfio-pci implementing > > > vendor ops to allow live migration of pass-through devices, is it > > > necessary to implement similar sysfs node for those devices? > > > or do you think just PCI IDs of those devices are enough for libvirt to > > > know device compatibility ? > > > > Wasn't the problem that we'd have to know how to check for things like: > > a) Whether different firmware versions in the device were actually > > compatible > > b) Whether minor hardware differences were compatible - e.g. some > > hardware might let you migrate to the next version of hardware up. > > Yes, minor changes in hardware or firmware that may not be represented > in the device ID or hardware revision. Also the version is as much for > indicating the compatibility of the vendor defined migration protocol > as it is for the hardware itself. I certainly wouldn't be so bold as > to create a protocol that is guaranteed compatible forever. We'll need > to expose the same sysfs attribute in some standard location for > non-mdev devices. I assume vfio-pci would provide the vendor ops some > mechanism to expose these in a standard namespace of sysfs attributes > under the device itself. Perhaps that indicates we need to link the > mdev type version under the mdev device as well to make this > transparent to userspace tools like libvirt. Thanks, > Got it. will do it. Thanks! Yan
