On Mon, Jun 25, 2018 at 10:52:41AM +0100, Peter Maydell wrote: > On 24 June 2018 at 23:10, Christoffer Dall <christoffer.dall@xxxxxxx> wrote: > > This small series addresses a peculiarity of the current VGIC > > implementation, namely that we don't support interrupt grouping. > > > > KVM either implements a GICv2 without support for the security > > extensions, or a GICv3 with DS=1. For GICv2, on systems without the > > security extensions, group 0 interrupts can be configured to be either > > signalled as FIQs or as IRQs by the VM, whereas group 1 interrupts are > > always IRQs. For GICv3, with DS=1, group 1 interrupts are always IRQs > > and group 0 interrupts are always FIQs, and there is no concept of > > secure vs. non-secure group 1 interrupts when DS=1. > > > > We were treating all interrupts on GICv2 as group 0, but yet telling the > > geust that they were group 1. The first patch changes this behavior, > > which seems to have no effect on no known guests, but still. > > > > The remaining patches introduce proper interrupt grouping support, along > > with MMIO accessors for the VM and userspace to retrieve and set the > > which group SGIs, PPIs, and SPIs belong to. LPIs are always group 1 > > interrupts as per the architecture, and there is no way to modify this > > configuration (no IGROUPR registers for LPIs or equivalent ITS > > commands). > > How do we handle migration compatibility here? For instance if > we have a guest running on an old kernel with GICv2, presumably > it reports the GICD_IGROUPRn to userspace as being all-1 (but > they behave as group 0); then when we load on the new kernel > the new kernel will honour the IGROUPRn values and the interrupts > will start behaving like group 1 ? Maybe this works because the > guest is expecting them to be signalled as IRQ either way... > Interesting. For GICv2, I think this will actually break, and the migrated Linux guest won't see any interrupts anymore (Linux only sets bit 0 in GICD_CTLR). For GICv3, everything stays group 1 unless the guest is specifically trying to configure group 0 for something. I suppose this means we need to let userspace request ARCH_COMPLIANT_GICV2 and otherwise ignore userspace writes to IGROUPR? Thanks, -Christoffer _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
