Re: KVM on ARM crashes with new VGIC v4.7-rc7

[Marc Zyngier <marc.zyngier@arm.com>]

On 25/07/16 07:14, Stefan Agner wrote:
> On 2016-07-24 05:36, Marc Zyngier wrote:
>> On Sun, 24 Jul 2016 13:22:55 +0100
>> Marc Zyngier <marc.zyngier@arm.com> wrote:
>>
>>> On Fri, 22 Jul 2016 10:56:44 -0700
>>> Stefan Agner <stefan@agner.ch> wrote:
>>>
>>>> On 2016-07-22 10:49, Marc Zyngier wrote:
>>>>> On 22/07/16 18:38, Andrew Jones wrote:
>>>>>> On Fri, Jul 22, 2016 at 04:40:15PM +0100, Marc Zyngier wrote:
>>>>>>> On 22/07/16 15:35, Andrew Jones wrote:
>>>>>>>> On Fri, Jul 22, 2016 at 11:42:02AM +0100, Andre Przywara wrote:
>>>>>>>>> Hi Stefan,
>>>>>>>>>
>>>>>>>>> On 22/07/16 06:57, Stefan Agner wrote:
>>>>>>>>>> Hi,
>>>>>>>>>>
>>>>>>>>>> I tried KVM on a Cortex-A7 platform (i.MX 7Dual SoC) and encountered
>>>>>>>>>> this stack trace immediately after invoking qemu-system-arm:
>>>>>>>>>>
>>>>>>>>>> Unable to handle kernel paging request at virtual address ffffffe4
>>>>>>>>>> pgd = 8ca52740
>>>>>>>>>> [ffffffe4] *pgd=80000080007003, *pmd=8ff7e003, *pte=00000000
>>>>>>>>>> Internal error: Oops: 207 [#1] SMP ARM
>>>>>>>>>> Modules linked in:
>>>>>>>>>> CPU: 0 PID: 329 Comm: qemu-system-arm Tainted: G        W
>>>>>>>>>> 4.7.0-rc7-00094-gea3ed2c #109
>>>>>>>>>> Hardware name: Freescale i.MX7 Dual (Device Tree)
>>>>>>>>>> task: 8ca3ee40 ti: 8d2b0000 task.ti: 8d2b0000
>>>>>>>>>> PC is at do_raw_spin_lock+0x8/0x1dc
>>>>>>>>>> LR is at kvm_vgic_flush_hwstate+0x8c/0x224
>>>>>>>>>> pc : [<8027c87c>]    lr : [<802172d4>]    psr: 60070013
>>>>>>>>>> sp : 8d2b1e38  ip : 8d2b0000  fp : 00000001
>>>>>>>>>> r10: 8d2b0000  r9 : 00010000  r8 : 8d2b8e54
>>>>>>>>>> fec 30be0000.ethernet eth0: MDIO read timeout
>>>>>>>>>> r7 : 8d2b8000  r6 : 8d2b8e74  r5 : 00000000  r4 : ffffffe0
>>>>>>>>>> r3 : 00004ead  r2 : 00000000  r1 : 00000000  r0 : ffffffe0
>>>>>>>>>> Flags: nZCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment user
>>>>>>>>>> Control: 30c5387d  Table: 8ca52740  DAC: fffffffd
>>>>>>>>>> Process qemu-system-arm (pid: 329, stack limit = 0x8d2b0210)
>>>>>>>>>> Stack: (0x8d2b1e38 to 0x8d2b2000)
>>>>>>>>>> 1e20:                                                       ffffffe0
>>>>>>>>>> 00000000
>>>>>>>>>> 1e40: 8d2b8e74 8d2b8000 8d2b8e54 00010000 8d2b0000 802172d4 8d2b8000
>>>>>>>>>> 810074f8
>>>>>>>>>> 1e60: 81007508 8ca5f800 8d284000 00010000 8d2b0000 8020fbd4 8ce9a000
>>>>>>>>>> 8ca5f800
>>>>>>>>>> 1e80: 00000000 00010000 00000000 00ff0000 8d284000 00000000 00000000
>>>>>>>>>> 7ffbfeff
>>>>>>>>>> 1ea0: fffffffe 00000000 8d28b780 00000000 755fec6c 00000000 00000000
>>>>>>>>>> ffffe000
>>>>>>>>>> 1ec0: 8d2b8000 00000000 8d28b780 00000000 755fec6c 8020af90 00000000
>>>>>>>>>> 8023f248
>>>>>>>>>> 1ee0: 0000000a 755fe98c 8d2b1f08 00000008 8021aa84 ffffe000 00000000
>>>>>>>>>> 00000000
>>>>>>>>>> 1f00: 8a00d860 8d28b780 80334f94 00000000 8d2b0000 80334748 00000000
>>>>>>>>>> 00000000
>>>>>>>>>> 1f20: 00000000 8d28b780 00004000 00000009 8d28b500 00000024 8104ebee
>>>>>>>>>> 80bc2ec4
>>>>>>>>>> 1f40: 80bafa24 8034138c 00000000 00000000 80341248 00000000 755fec6c
>>>>>>>>>> 007c1e70
>>>>>>>>>> 1f60: 00000009 00004258 0000ae80 8d28b781 00000009 8d28b780 0000ae80
>>>>>>>>>> 00000000
>>>>>>>>>> 1f80: 8d2b0000 00000000 755fec6c 80334f94 007c1e70 322a7400 00004258
>>>>>>>>>> 00000036
>>>>>>>>>> 1fa0: 8021aa84 8021a900 007c1e70 322a7400 00000009 0000ae80 00000000
>>>>>>>>>> 755feac0
>>>>>>>>>> 1fc0: 007c1e70 322a7400 00004258 00000036 7e9aff58 01151da4 76f8b4c0
>>>>>>>>>> 755fec6c
>>>>>>>>>> 1fe0: 0038192c 755fea9c 00048ae7 7697d66c 60070010 00000009 00000000
>>>>>>>>>> 00000000
>>>>>>>>>> [<8027c87c>] (do_raw_spin_lock) from [<802172d4>]
>>>>>>>>>> (kvm_vgic_flush_hwstate+0x8c/0x224)
>>>>>>>>>> [<802172d4>] (kvm_vgic_flush_hwstate) from [<8020fbd4>]
>>>>>>>>>> (kvm_arch_vcpu_ioctl_run+0x110/0x478)
>>>>>>>>>> [<8020fbd4>] (kvm_arch_vcpu_ioctl_run) from [<8020af90>]
>>>>>>>>>> (kvm_vcpu_ioctl+0x2e0/0x6d4)
>>>>>>>>>> [<8020af90>] (kvm_vcpu_ioctl) from [<80334748>]
>>>>>>>>>> (do_vfs_ioctl+0xa0/0x8b8)
>>>>>>>>>> [<80334748>] (do_vfs_ioctl) from [<80334f94>] (SyS_ioctl+0x34/0x5c)
>>>>>>>>>> [<80334f94>] (SyS_ioctl) from [<8021a900>] (ret_fast_syscall+0x0/0x1c)
>>>>>>>>>> Code: e49de004 ea09ea24 e92d47f0 e3043ead (e5902004)
>>>>>>>>>> ---[ end trace cb88537fdc8fa206 ]---
>>>>>>>>>>
>>>>>>>>>> I use CONFIG_KVM_NEW_VGIC=y. This happens to me with a rather minimal
>>>>>>>>>> qemu invocation (qemu-system-arm -enable-kvm -M virt -cpu host
>>>>>>>>>> -nographic -serial stdio -kernel zImage).
>>>>>>>>>>
>>>>>>>>>> Using a bit older Qemu version 2.4.0.
>>>>>>>>>
>>>>>>>>> I just tried with a self compiled QEMU 2.4.0 and the Ubuntu 14.04
>>>>>>>>> provided 2.0.0, it worked fine with Linus' current HEAD as a host kernel
>>>>>>>>> on a Midway (Cortex-A15).
>>>>>>>>
>>>>>>>> I can reproduce the issue with a latest QEMU build on AMD Seattle
>>>>>>>> (I haven't tried anywhere else yet)
>>>>>>>>
>>>>>>>>>
>>>>>>>>> Can you try to disable the new VGIC, just to see if that's a regression?
>>>>>>>>
>>>>>>>> Disabling NEW_VGIC "fixes" guest boots.
>>>>>>>>
>>>>>>>> I'm not using defconfig for my host kernel. I'll do a couple more
>>>>>>>> tests and provide a comparison of my config vs. a defconfig in
>>>>>>>> a few minutes.
>>>>>>>
>>>>>>> Damn. It is not failing for me, so it has to be a kernel config thing...
>>>>>>> If you can narrow it down to the difference with defconfig, that'd be
>>>>>>> tremendously helpful.
>>>>>>
>>>>>> It's PAGE_SIZE; 64K doesn't work, 4K does, regardless of VA_BITS
>>>>>> selection.
>>>>>
>>>>> That definitely doesn't match Stefan's report (32bit only has 4k). I'll
>>>>
>>>> Hehe, was just plowing through code and came to that conclusion, glad I
>>>> got that right :-)
>>>>
>>>> What defconfig do you use? I could reproduce the issue also with
>>>> multi_v7_defconfig + ARM_LPAE + KVM.
>>>
>>> I'm now on -rc7 with multi_v7_defconfig + LPAE + KVM (and everything
>>> built-in to make my life simpler). The host works perfectly, and I can
>>> spawn VMs without any issue.
>>>
>>> I've tested with QEMU emulator version 2.2.0 (Debian 1:2.2+dfsg-5exp)
>>> as packaged with Jessie from a while ago. I've also upgraded the box to
>>> something more recent (2.5), same effect.
>>>
>>>>
>>>> Btw, I am not exactly on vanilla 4.7-rc7, I merged Shawns for-next +
>>>> clock next to get to the bits and pieces required for my board...
>>>>
>>>> That said, it works fine otherwise, and the stacktrace looks rather
>>>> platform independent...
>>>
>>> Indeed, and if these clocks were doing anything unsavoury, we'd
>>> probably see other things exploding. So we need to find out where we
>>> are diverging.
>>>
>>> What compiler are you using? I just noticed that my build
>>> infrastructure is a bit outdated for 32bit ARM (gcc 4.9.2), so I'm
>>> going to upgrade that to gcc 5.3 and retest.
>>
>> Same thing. The damn thing stubbornly works.
>>
>> Please send your full configuration, compiler version, exact QEMU
>> command line, and any other detail that could be vaguely relevant. As
>> the old VGIC gets removed in 4.8, we definitely need to nail that
>> sucker right now.
> 
> I built the kernel with
> gcc-linaro-5.2-2015.11-2-x86_64_arm-linux-gnueabihf the binaries built
> by Linaro (full config attached). For the Rootfs (and Qemu) I did use
> the same compiler version, but built using OpenEmbedded.
> 
> Running on a Colibri module using NXP i.MX 7Dual SoC, I haven't used it
> that much on mainline but it seems to be rather stable so far.
> 
> I can reproduce the issue with a minimal command such as this:
> qemu-system-arm -enable-kvm -M virt -cpu host
> 
> [  179.430694] Unable to handle kernel paging request at virtual address
> fffffffc
> What is puzzling me a bit that the address the kernel tries to access is
> constantly 0xfffffffc. This would be -4, which would be -EINTR? A
> unhandled error return?

Your initial report had 0xffffffe4 instead. Which looks a bit like a
"container_of" operation on a NULL pointer. Do you always get the same
backtrace? If so, any chance you could run a

arm-linux-gnueabihf-addr2line -e vmlinux -i TheCrashingPC

so that we get an idea of which lock we're crashing on?

I'm about to try your own config to see if I get somewhere.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...