On Sun, Feb 15 2015 at 3:07:50 pm GMT, Jan Kiszka <jan.kiszka@xxxxxx> wrote: > On 2015-02-15 15:59, Marc Zyngier wrote: >> On Sun, Feb 15 2015 at 2:40:40 pm GMT, Jan Kiszka <jan.kiszka@xxxxxx> wrote: >>> On 2015-02-15 14:37, Marc Zyngier wrote: >>>> On Sun, Feb 15 2015 at 8:53:30 am GMT, Jan Kiszka >>>> <jan.kiszka@xxxxxx> wrote: >>>>> I'm now throwing trace_printk at my broken KVM. Already found out that I >>>>> get ARM_EXCEPTION_IRQ every few 10 µs. Not seeing any irq_* traces, >>>>> though. Weird. >>>> >>>> This very much looks like a screaming interrupt. At such a rate, no >>>> wonder your VM make much progress. Can you find out which interrupt is >>>> screaming like this? Looking at GICC_HPPIR should help, but you'll have >>>> to map the CPU interface in HYP before being able to access it there. >>> >>> OK... let me figure this out. I had this suspect as well - the host gets >>> a VM exit for each injected guest IRQ? >> >> Not exactly. There is a VM exit for each physical interrupt that fires >> while the guest is running. Injecting an interrupt also causes a VM >> exit, as we force the vcpu to reload its context. > > Ah, GICC != GICV - you are referring to host-side pending IRQs. Any > hints on how to get access to that register would accelerate the > analysis (ARM KVM code is still new to me). Map the GICC region in HYP using create_hyp_io_mapping (see vgic_v2_probe for an example of how we map GICH), and stash the read of GICC_HPPIR before leaving HYP mode (and before saving the guest timer). BTW, when you look at /proc/interrupts on the host, don't you see an interrupt that's a bit too eager to fire? >>> BTW, I also tried with in-kernel GIC disabled (in the kernel config), >>> but I guess that's pointless. Linux seems to be stuck on a >>> non-functional architectural timer then, right? >> >> Yes. Useful for bringup, but nothing more. > > Maybe we should perform a feature check and issue a warning from QEMU? I'd assume this is already in place (but I almost never run QEMU, so I could be wrong here). >> I still wonder if the 4+1 design on the K1 is not playing tricks behind >> our back. Having talked to Ian Campbell earlier this week, he also can't >> manage to run guests in Xen on this platform, so there's something >> rather fishy here. > > Interesting. The announcements of his PSCI patches [1] sounded more > promising. Maybe it was only referring to getting the hypervisor itself > running... This is my understanding so far. > To my current (still limited understanding) of that platform would say > that this little core is parked after power-up of the main APs. And as > we do not power them down, there is no reason to perform a cluster > switch or anything similarly nasty, no? I can't see why this would happen, but I've learned not to assume anything when it come to braindead creativity on the HW side... M. -- Without deviation from the norm, progress is not possible. -- 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
