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 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 ?

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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>
>
> .
>