On 6 June 2012 16:55, Christoffer Dall <c.dall at virtualopensystems.com> wrote: > On Wed, Jun 6, 2012 at 6:07 AM, Marc Zyngier <marc.zyngier at arm.com> wrote: >> There is probably several configurations we want to support: >> - Cortex-A7/15 host and guest: VGIC + ARCH_TIMER mandatory, or at least >> be the default configuration. >> - Hypothetical v7 + virt extensions but without VGIC: QEMU GIC emulation >> + whatever timer the guest wants to use (and that QEMU provides). >> >> Whether or not someone will build this hypothetical v7, I have no idea. >> But the fact that someone *could* build such a thing means we should >> keep our interrupt injection code flexible enough. > > agreed > >> >> When it comes to the architected timer, it is practically impossible to >> use it in a guest without VGIC support. Even worse, it is impossible to >> hide it from the guest. >> > > so if there's architected timer support, mandate that the guest uses > it, and make architected timer support rely on VGIC support is our > scheme, right? We don't need to mandate that the guest uses it (it's fine for the guest to completely ignore it). What is mandatory is that it has to be implemented in KVM via the virtual timer + VGIC combo -- you can't implement the arch. timers purely by dumping out to QEMU userspace. -- PMM
