On 14 March 2016 at 11:13, Andre Przywara <andre.przywara@xxxxxxx> wrote: > So I see two ways to fix this: > 1.) we find a KVM specific way of letting userland save and restore the > ITS tables directly > 2.) we implement the BASER<n> registers, but still use our "cache" for > normal operations. On demand we would serialize KVM's virtual ITS data > structures and put them into the guest's memory, so they could be > saved/restored from there. I feel like we're rehashing a bunch of design choices we talked through way back in the last-but-one Connect. I don't suppose anybody wrote down our rationales from back then? (In particular I forget whether we decided the ITS tables were large enough to need to allow some sort of before-the-VM-stops migration of the data, which would be relatively doable with option 2 but painful under option 1.) >> Only caveat there I think was that we had to decide on a storage format >> in those memory regions, to allow QEMU to understand the state and to >> ensure back/forwards compatibility between KVM versions. > > Do we need QEMU to actually understand this? Can't we just leave this > all to the kernel and QEMU just passes on the data? That would still > require some ABI stability between kernel versions in this respect, but > it's less problematic than exposing the data format to userland at all. This would preclude ever being able to migrate a VM from KVM to TCG QEMU, which seems a shame. (That doesn't work right now, but I'm a bit wary of shutting the door to it forever.) thanks -- PMM -- 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
