On 2015-02-15 16:30, Marc Zyngier wrote: > 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). OK. > > BTW, when you look at /proc/interrupts on the host, don't you see an > interrupt that's a bit too eager to fire? No - but that makes sense given that we do not enter any interrupt handler according to ftrace, thus there can't be any counter incrementation. > >>>> 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). Nope, QEMU starts up fine, just lets the guest starve while waiting for jiffies to increase. > >>> 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... True. Jan
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