From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marc Zyngier Subject: Re: arm: warning at virt/kvm/arm/vgic.c:1468 Date: Sun, 15 Feb 2015 15:30:03 +0000 Message-ID: <87k2zjdwg4.fsf@why.wild-wind.fr.eu.org> References: <54D714B9.6090106@web.de> <20150213044613.GA47577@lvm> <87k2zms4ub.fsf@linaro.org> <87iof6s3o7.fsf@linaro.org> <54E05E8A.5020109@web.de> <87wq3je1o4.fsf@why.wild-wind.fr.eu.org> <54E0AFE8.20202@web.de> <87oaovdxvb.fsf@why.wild-wind.fr.eu.org> <54E0B646.6030601@web.de> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <54E0B646.6030601@web.de> (Jan Kiszka's message of "Sun, 15 Feb 2015 15:07:50 +0000") Sender: kvm-owner@vger.kernel.org To: Jan Kiszka Cc: Alex =?utf-8?Q?Benn=C3=A9e?= , Christoffer Dall , kvmarm , kvm , Paolo Bonzini , Wei Huang List-Id: kvmarm@lists.cs.columbia.edu On Sun, Feb 15 2015 at 3:07:50 pm GMT, Jan Kiszka = wrote: > On 2015-02-15 15:59, Marc Zyngier wrote: >> On Sun, Feb 15 2015 at 2:40:40 pm GMT, Jan Kiszka wrote: >>> On 2015-02-15 14:37, Marc Zyngier wrote: >>>> On Sun, Feb 15 2015 at 8:53:30 am GMT, Jan Kiszka >>>> wrote: >>>>> I'm now throwing trace_printk at my broken KVM. Already found out= that I >>>>> get ARM_EXCEPTION_IRQ every few 10 =C2=B5s. Not seeing any irq_* = traces, >>>>> though. Weird. >>>> >>>> This very much looks like a screaming interrupt. At such a rate, n= o >>>> wonder your VM make much progress. Can you find out which interrup= t 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 the= re. >>> >>> OK... let me figure this out. I had this suspect as well - the host= gets >>> a VM exit for each injected guest IRQ? >>=20 >> Not exactly. There is a VM exit for each physical interrupt that fir= es >> while the guest is running. Injecting an interrupt also causes a VM >> exit, as we force the vcpu to reload its context. > > Ah, GICC !=3D 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? >>=20 >> 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 beh= ind >> our back. Having talked to Ian Campbell earlier this week, he also c= an'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 itse= lf > running... This is my understanding so far. > To my current (still limited understanding) of that platform would sa= y > that this little core is parked after power-up of the main APs. And a= s > 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. --=20 Without deviation from the norm, progress is not possible.