On 11/12/12 18:27, Andreas Sandberg wrote: > On 11/12/12 15:46, Christoffer Dall wrote: >> On Tue, Dec 11, 2012 at 12:41 AM, Simon Baines >> <simonbaines2012@xxxxxxxxxxx> wrote: >>> someone can briefly explain what would be the drawback of not using the >>> architected timer support when running KVM on ARM? >>> Is it possible to run guests without that architected timer configuration >>> enabled? >> It's possible, in which case you need to use an emulated piece of >> timer hardware, which will cause you a lot more vmexits to interact >> with the timer to program it, for example. > > Is this really the case? I was under the impression that this would > require qemu (or gem5 in my case) to emulate CP15 accesses to registers > which aren't normally exposed to user space. I tried to boot a recent > Linux kernel using KVM last week and I'm pretty sure the host kernel > sent an illegal instruction trap to the guest when it tried to enable > the timers using the co-processor interface. What makes matters more > complicated is that the timer can't be hidden from the guest since > ID_PFR1 is invariant. You probably tried to use the physical timers, which we reserve for the host. If you use a recent enough guest, it will default to use virtual timers, which is always available. No traps involved in this case. M. -- Jazz is not dead. It just smells funny... _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/cucslists/listinfo/kvmarm
