Re: arm: warning at virt/kvm/arm/vgic.c:1468

[Christoffer Dall <christoffer.dall@linaro.org>]

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On Fri, Feb 13, 2015 at 07:21:20AM +0100, Jan Kiszka wrote:
> Hi Christoffer,
> 
> On 2015-02-13 05:46, Christoffer Dall wrote:
> > Hi Jan,
> > 
> > On Sun, Feb 08, 2015 at 08:48:09AM +0100, Jan Kiszka wrote:
> >> Hi,
> >>
> >> after fixing the VM_BUG_ON, my QEMU guest on the Jetson TK1 generally
> >> refuses to boot. Once in a while it does, but quickly gets stuck again.
> >> In one case I found this in the kernel log (never happened again so
> >> far):
> >>
> >> [  762.022874] WARNING: CPU: 1 PID: 972 at ../arch/arm/kvm/../../../virt/kvm/arm/vgic.c:1468 kvm_vgic_sync_hwstate+0x314/0x344()
> >> [  762.022884] Modules linked in:
> >> [  762.022902] CPU: 1 PID: 972 Comm: qemu-system-arm Not tainted 3.19.0-rc7-00221-gfd7a168-dirty #13
> >> [  762.022911] Hardware name: NVIDIA Tegra SoC (Flattened Device Tree)
> >> [  762.022937] [<c0025d80>] (unwind_backtrace) from [<c00215d8>] (show_stack+0x10/0x14)
> >> [  762.022958] [<c00215d8>] (show_stack) from [<c065f494>] (dump_stack+0x98/0xd8)
> >> [  762.022976] [<c065f494>] (dump_stack) from [<c0035f38>] (warn_slowpath_common+0x80/0xb0)
> >> [  762.022991] [<c0035f38>] (warn_slowpath_common) from [<c0036004>] (warn_slowpath_null+0x1c/0x24)
> >> [  762.023007] [<c0036004>] (warn_slowpath_null) from [<c001c3c4>] (kvm_vgic_sync_hwstate+0x314/0x344)
> >> [  762.023024] [<c001c3c4>] (kvm_vgic_sync_hwstate) from [<c00147c0>] (kvm_arch_vcpu_ioctl_run+0x210/0x400)
> >> [  762.023041] [<c00147c0>] (kvm_arch_vcpu_ioctl_run) from [<c001063c>] (kvm_vcpu_ioctl+0x2e4/0x6ec)
> >> [  762.023059] [<c001063c>] (kvm_vcpu_ioctl) from [<c01098a4>] (do_vfs_ioctl+0x40c/0x600)
> >> [  762.023076] [<c01098a4>] (do_vfs_ioctl) from [<c0109acc>] (SyS_ioctl+0x34/0x5c)
> >> [  762.023091] [<c0109acc>] (SyS_ioctl) from [<c001e320>] (ret_fast_syscall+0x0/0x34)
> > 
> > so this means your guest caused a maintenance interrupt and the bit is
> > set in the GICH_EISR for the LR in question but the link register state
> > is not 0, which is in direct violation of the GIC spec.  Hmmmm.
> > 
> > You're not doing any IRQ forwarding stuff or device passthrough here are
> > you?
> 
> No, just boring emulation. The command line is
> 
> qemu-system-ar -machine vexpress-a15 -kernel zImage -serial mon:stdio
> -append 'console=ttyAMA0 root=/dev/mmcblk0 rw' -snapshot -sd
> OpenSuse13-1_arm.img -dtb vexpress-v2p-ca15-tc1.dtb -s -enable-kvm
> 
> > 
> >>
> >>
> >> BTW, KVM tracing support on ARM seems like it requires some care. E.g.:
> >> kvm_exit does not report an exit reason. The in-kernel vgic also seems
> >> to lack instrumentation. Unfortunate. Tracing is usually the first stop
> >> when KVM is stuck on a guest.
> > 
> > I know, the exit reason is on my todo list, and Alex B is sitting on
> > trace patches for the gic.  Coming soon to a git repo near your.
> 
> Cool, looking forward.
> 
> Next thing I noticed is that guest debugging via qemu causes troubles in
> kvm mode. For some reason, qemu is unable to write soft-breakpoints,
> thus not even a single-step works. Also known?
> 
Yes, Alex Bennee is working on this.

-Christoffer

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