On Wed, Jun 25, 2014 at 8:03 AM, Marc Zyngier <marc.zyngier@xxxxxxx> wrote: > On Wed, Jun 25 2014 at 01:50:12 PM, Rob Herring <robherring2@xxxxxxxxx> wrote: >> On Wed, Jun 25, 2014 at 4:28 AM, Marc Zyngier <marc.zyngier@xxxxxxx> wrote: >>> So far, GICv2 has been used in with EOImode == 0. The effect of this >>> mode is to perform the priority drop and the deactivation of the >>> interrupt at the same time. >>> >>> While this works perfectly for Linux (we only have a single priority), >>> it causes issues when an interrupt is forwarded to a guest, and when >>> we want the guest to perform the EOI itself. >>> >>> For this case, the GIC architecture provides EOImode == 1, where: >>> - A write to the EOI register drops the priority of the interrupt and leaves >>> it active. Other interrupts at the same priority level can now be taken, >>> but the active interrupt cannot be taken again >>> - A write to the DIR marks the interrupt as inactive, meaning it can >>> now be taken again. >>> >>> We only enable this feature when booted in HYP mode. Also, as most device >>> trees are broken (they report the CPU interface size to be 4kB, while >>> the GICv2 CPU interface size is 8kB), output a warning if we're booted >>> in HYP mode, and disable the feature. >> >> Why not fix-up the size so the feature can be enabled? > > Is it a bet we're willing to take? We'd end-up with a kernel that > doesn't boot if the DT was actually right. If we stay with EOImode==0, > we can still boot (KVM will probably be broken though). I think so. Seems like your last statement answers this. Why is KVM not working on my system seems like a much more likely and frequent support issue than a potentially broken system. The only place I really could see it be broken is an SBSA system doing the address swizzling trick with the gic-400 to get 64KB spaced regions but does not use the 60KB aligned cpu interface address. But DTBs are hardly stable for 64-bit systems and can be updated. Rob _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
