On Tue, May 10, 2016 at 03:15:12PM +0100, 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 :-) > Agreed with all of the above. My nit here is simply that if we don't implement grouping support now, then it's just a gross hack, and we should just state that until we fix it properly. -Christoffer -- 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
