Re: [Qemu-devel] [BUG/RFC] Two cpus are not brought up normally in SLES11 sp3 VM after reboot

[zhanghailiang <zhang.zhanghailiang@huawei.com>]

On 2015/7/7 20:21, Igor Mammedov wrote:
> On Tue, 7 Jul 2015 19:43:35 +0800
> zhanghailiang <zhang.zhanghailiang@huawei.com> wrote:
>
>> On 2015/7/7 19:23, Igor Mammedov wrote:
>>> On Mon, 6 Jul 2015 17:59:10 +0800
>>> zhanghailiang <zhang.zhanghailiang@huawei.com> wrote:
>>>
>>>> On 2015/7/6 16:45, Paolo Bonzini wrote:
>>>>>
>>>>>
>>>>> On 06/07/2015 09:54, zhanghailiang wrote:
>>>>>>
>>>>>>    From host, we found that QEMU vcpu1 thread and vcpu7 thread were not
>>>>>> consuming any cpu (Should be in idle state),
>>>>>> All of VCPUs' stacks in host is like bellow:
>>>>>>
>>>>>> [<ffffffffa07089b5>] kvm_vcpu_block+0x65/0xa0 [kvm]
>>>>>> [<ffffffffa071c7c1>] __vcpu_run+0xd1/0x260 [kvm]
>>>>>> [<ffffffffa071d508>] kvm_arch_vcpu_ioctl_run+0x68/0x1a0 [kvm]
>>>>>> [<ffffffffa0709cee>] kvm_vcpu_ioctl+0x38e/0x580 [kvm]
>>>>>> [<ffffffff8116be8b>] do_vfs_ioctl+0x8b/0x3b0
>>>>>> [<ffffffff8116c251>] sys_ioctl+0xa1/0xb0
>>>>>> [<ffffffff81468092>] system_call_fastpath+0x16/0x1b
>>>>>> [<00002ab9fe1f99a7>] 0x2ab9fe1f99a7
>>>>>> [<ffffffffffffffff>] 0xffffffffffffffff
>>>>>>
>>>>>> We looked into the kernel codes that could leading to the above 'Stuck'
>>>>>> warning,
>>> in current upstream there isn't any printk(...Stuck...) left since that code path
>>> has been reworked.
>>> I've often seen this on over-committed host during guest CPUs up/down torture test.
>>> Could you update guest kernel to upstream and see if issue reproduces?
>>>
>>
>> Hmm, Unfortunately, it is very hard to reproduce, and we are still trying to reproduce it.
>>
>> For your test case, is it a kernel bug?
>> Or is there any related patch could solve your test problem been merged into
>> upstream ?
> I don't remember all prerequisite patches but you should be able to find
>    http://marc.info/?l=linux-kernel&m=140326703108009&w=2
>    "x86/smpboot: Initialize secondary CPU only if master CPU will wait for it"
> and then look for dependencies.
>

Er, we have investigated this patch, and it is not related to our problem, :)

Thanks.

>
>>
>> Thanks,
>> zhanghailiang
>>
>>>>>> and found that the only possible is the emulation of 'cpuid' instruct in
>>>>>> kvm/qemu has something wrong.
>>>>>> But since we can’t reproduce this problem, we are not quite sure.
>>>>>> Is there any possible that the cupid emulation in kvm/qemu has some bug ?
>>>>>
>>>>> Can you explain the relationship to the cpuid emulation?  What do the
>>>>> traces say about vcpus 1 and 7?
>>>>
>>>> OK, we searched the VM's kernel codes with the 'Stuck' message, and  it is located in
>>>> do_boot_cpu(). It's in BSP context, the call process is:
>>>> BSP executes start_kernel() -> smp_init() -> smp_boot_cpus() -> do_boot_cpu() -> wakeup_secondary_via_INIT() to trigger APs.
>>>> It will wait 5s for APs to startup, if some AP not startup normally, it will print 'CPU%d Stuck' or 'CPU%d: Not responding'.
>>>>
>>>> If it prints 'Stuck', it means the AP has received the SIPI interrupt and begins to execute the code
>>>> 'ENTRY(trampoline_data)' (trampoline_64.S) , but be stuck in some places before smp_callin()(smpboot.c).
>>>> The follow is the starup process of BSP and AP.
>>>> BSP:
>>>> start_kernel()
>>>>      ->smp_init()
>>>>         ->smp_boot_cpus()
>>>>           ->do_boot_cpu()
>>>>               ->start_ip = trampoline_address(); //set the address that AP will go to execute
>>>>               ->wakeup_secondary_cpu_via_init(); // kick the secondary CPU
>>>>               ->for (timeout = 0; timeout < 50000; timeout++)
>>>>                   if (cpumask_test_cpu(cpu, cpu_callin_mask)) break;// check if AP startup or not
>>>>
>>>> APs:
>>>> ENTRY(trampoline_data) (trampoline_64.S)
>>>>          ->ENTRY(secondary_startup_64) (head_64.S)
>>>>             ->start_secondary() (smpboot.c)
>>>>                ->cpu_init();
>>>>                ->smp_callin();
>>>>                    ->cpumask_set_cpu(cpuid, cpu_callin_mask); ->Note: if AP comes here, the BSP will not prints the error message.
>>>>
>>>>    From above call process, we can be sure that, the AP has been stuck between trampoline_data and the cpumask_set_cpu() in
>>>> smp_callin(), we look through these codes path carefully, and only found a 'hlt' instruct that could block the process.
>>>> It is located in trampoline_data():
>>>>
>>>> ENTRY(trampoline_data)
>>>>            ...
>>>>
>>>> 	call	verify_cpu		# Verify the cpu supports long mode
>>>> 	testl   %eax, %eax		# Check for return code
>>>> 	jnz	no_longmode
>>>>
>>>>            ...
>>>>
>>>> no_longmode:
>>>> 	hlt
>>>> 	jmp no_longmode
>>>>
>>>> For the process verify_cpu(),
>>>> we can only find the 'cpuid' sensitive instruct that could lead VM exit from No-root mode.
>>>> This is why we doubt if cpuid emulation is wrong in KVM/QEMU that leading to the fail in verify_cpu.
>>>>
>>>>    From the message in VM, we know vcpu1 and vcpu7 is something wrong.
>>>> [    5.060042] CPU1: Stuck ??
>>>> [   10.170815] CPU7: Stuck ??
>>>> [   10.171648] Brought up 6 CPUs
>>>>
>>>> Besides, the follow is the cpus message got from host.
>>>> 80FF72F5-FF6D-E411-A8C8-000000821800:/home/fsp/hrg # virsh qemu-monitor-command instance-0000000
>>>> * CPU #0: pc=0x00007f64160c683d thread_id=68570
>>>>      CPU #1: pc=0xffffffff810301f1 (halted) thread_id=68573
>>>>      CPU #2: pc=0xffffffff810301e2 (halted) thread_id=68575
>>>>      CPU #3: pc=0xffffffff810301e2 (halted) thread_id=68576
>>>>      CPU #4: pc=0xffffffff810301e2 (halted) thread_id=68577
>>>>      CPU #5: pc=0xffffffff810301e2 (halted) thread_id=68578
>>>>      CPU #6: pc=0xffffffff810301e2 (halted) thread_id=68583
>>>>      CPU #7: pc=0xffffffff810301f1 (halted) thread_id=68584
>>>>
>>>> Oh, i also forgot to mention in the above message that, we have bond each vCPU to different physical CPU in
>>>> host.
>>>>
>>>> Thanks,
>>>> zhanghailiang
>>>>
>>>>
>>>>
>>>>
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>>>
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