Marc, On 11/04/2017 12:05, Marc Zyngier wrote: > On 10/04/17 16:17, Auger Eric wrote: >> Hi Marc, >> >> On 10/04/2017 16:57, Marc Zyngier wrote: >>> 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? >> At the moment migration from B to C will fail because source ABI rev = >> v2 > destination support ABI = v1. >> >> A (v1) -> B (v1 & v2): migration OK >> B (v1 & v2) -> C (v1): migration NOK > > So what does IIDR report on B once the A->B migration has taken place? > Does it report v2? yes that was the plan Thanks Eric > > Thanks, > > M. >
