On 14/08/15 13:26, Pavel Fedin wrote: > Hello! Thank you for quick response. > >> This is fairly unreadable. Please use a switch statement instead. > > Christoffer disliked it in v1, so i thought a bit and changed it. Ok, will change it back. > >> And here, we're going to assume that the arch timer still usable. We >> definitely need a way to *prevent* the timer to be used when there is no >> GIC. Otherwise, we're going to start trying to setup the mapping for the >> active state, and the guest may start poking it. > > But, this seems to be already done, isn't it? > According to http://lxr.free-electrons.com/source/arch/arm/kvm/arm.c#L439: > --- cut --- > 459 /* > 460 * Enable the arch timers only if we have an in-kernel VGIC > 461 * and it has been properly initialized, since we cannot handle > 462 * interrupts from the virtual timer with a userspace gic. > 463 */ > 464 if (irqchip_in_kernel(kvm) && vgic_initialized(kvm)) > 465 kvm_timer_enable(kvm); > --- cut --- Right, I failed to remember that one. Sorry. It should be safe then. Hopefully. [...] > And some more. Actually, it is possible to emulate generic timer in userspace, just not the virtual > one. IIRC access to physical timer can be trapped. So, if we modify guest's device tree by removing > virtual timer IRQ, the guest will fall back to physical timer. And this will be caught by the > hypervisor. After this all we have to do is to add corresponding exit code which would allow the > userspace to emulate missing CP15 (or system in case of ARM64) registers. So, this timer issue is > not grave, just i postpone implementing it until GIC issues are settled down. This is completely Linux-specific, unfortunately. And it relies on userpace to expose a modified DT, so you need to be able to report back to userspace that you can't deal with the virtual timer. Which brings me to the next point: how do you tell userspace that your timers are non-functional? 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
