On 10/05/16 15:15, Peter Maydell wrote: > On 10 May 2016 at 15:04, Christoffer Dall <christoffer.dall@xxxxxxxxxx> wrote: >> On Fri, May 06, 2016 at 11:45:32AM +0100, Andre Przywara wrote: >>> + /* >>> + * Currently all guest IRQs are Group1, as Group0 would result >>> + * in a FIQ in the guest, which it wouldn't expect. >> >> I still don't like or understand this comment. This should simply say >> that we're making a gross assumption about all interrupts being group1 >> here. > > It's not really an assumption so much as it's a missing feature (aka bug): > there's no reason the vGIC shouldn't support group 0 interrupts. We > just get away with only supporting group 1 because Linux guests > happen to only use group 1 interrupts. If/when the vGIC gains support > for group0 interrupts, then it should reset with interrupts configured > in group0 by default. > >>> + * Eventually we want to make this configurable, so we may >>> + * revisit this in the future. >>> + */ > > The only reason to make it configurable is to work around a guest > kernel bug whereby Linux assumes that all interrupts start out > in Group1. Marc sent out a patch earlier today that fixes that bug: > https://lkml.org/lkml/2016/5/10/297 > Depending on how long it takes you to fix this missing vgic feature, > such kernels may all be long-forgotten, in which case you can > get away without the config option :-) I've CC'd stable for this particular patch, so hopefully we won't have to make it configurable as people will diligently update their kernels... I also have a patch for handling both groups in KVM, but I'll hold onto it until we have something we agree on for the bulk of the code. Thanks, M. -- Jazz is not dead. It just smells funny... -- 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