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

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

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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?

> 
> 
> 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.

-Christoffer

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