On 16 October 2013 02:49, Marc Zyngier <marc.zyngier@xxxxxxx> wrote: > On 16/10/13 00:21, Christoffer Dall wrote: >> On Mon, Oct 14, 2013 at 09:43:04AM +0100, Marc Zyngier wrote: >>> On 13/10/13 02:09, Christoffer Dall wrote: >>>> On Tue, Oct 08, 2013 at 06:17:08PM +0100, Marc Zyngier wrote: >>>>> It appears we have an arbitrary limitation where we refuse to >>>>> create more than 4 virtual A15 in a single VM. >>>>> >>>>> This limitation doesn't make much sense (the number 4 probably >>>>> comes from the maximum number of CPUs in a A15 cluster, but >>>>> KVM doesn't have any notion of cluster), and directly >>>>> contradicts CONFIG_MAX_VCPUS. >>>> >>>> So this comes from the early days where I looked at the A15 TRM and the >>>> MPIDR bit field for the CPU ID is limited to 2 bits. Exactly because >>>> I wasn't sure what remifications (if any) it would have to start >>>> populating this register with cluster id = (vcpu_id / 4) and cpu id = >>>> (vcpu_id % 4) I put this nice arbitrary restriction in there. >>>> >>>> I think we need to fix how we show this register to the guest >>>> otherwise... No? >>> >>> I don't see this being an issue, but if we really want to be 100% true >>> to the A15/A7 TRM, we can always compute MPIDR that way, and adjust >>> L2CTLR as well. >> >> Even with mach-virt we're still pretending to be an A15/A7 right? I >> think we should adhere to that. Is there some other reason why people >> shouldn't generally expect MPIDR to be correct (merging this code to KVM >> and running in a VM notwithstanding)? > > Yes, it is probably better to adhere to the law of least surprise. I'm > reworking this patch and will repost (slightly longer) the series. > >>> >>> That will require some userspace change in kvmtool though (need to >>> change the DT generator to cope with the cluster ID). >>> >> That would be the less fun part... > > Actually, it is surprisingly easy once the kernel does the right thing. > Great ;) _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/cucslists/listinfo/kvmarm
