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

[Igor Mammedov]

On Mon, 6 Jul 2015 17:59:10 +0800
zhanghailiang <address@hidden> 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?

> >> 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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