On 10/04/17 15:32, Auger Eric wrote: > Hi Marc, > > On 08/04/2017 12:42, Marc Zyngier wrote: >> On Mon, Mar 27 2017 at 10:30:58 AM, Eric Auger <eric.auger@xxxxxxxxxx> wrote: >>> The GITS_IIDR revision field is used to encode the version of the >>> table layout (ABI). So we need to restore it to check the table >>> layout to be restored is compatible with the destination vITS. >>> >>> The user selected revision is stored in the user_revision field. >>> It will be compared against the REV num at table restoration time. >> >> Why isn't it sufficient to keep it GITS_IIDR RO and let userspace find >> out about the ABI revision that the kernel understands? >> >> Or are we planning on supporting multiple ABIs in the kernel? > Yes as discussed with Peter, the plan is to allow several ABIs. So the > userspace informs the destination about the ABI revision of the stored > tables (contained by the GITS_IIDR). If the destination KVM does not > support this ABI revision, table restore will fail. > If so, do >> we have a deprecation policy/plan? I don't mind either way, but it would >> be good to document it... >> >> Maybe it is documented already and I missed it (which is perfectly >> possible!). > Well this is partly documented in > Documentation/virtual/kvm/devices/arm-vgic-its.txt. No plan to > deprecate. migration from KVM supporting v1 to KVM supporting V2 would > be possible but not the contrary. > > Does it make sense? Sort of. Say you have three systems: A and C, which only supports v1; B, which supports v1 and v2. Let's say you migrate from A to B, and from B to C. Is B mandated to be able to export the tables as v1 and v2? Or can it restrict what it can export? Thanks, M. -- Jazz is not dead. It just smells funny...
