Re: [PATCH 05/16] xen/percpu: don't initialize percpu on resume

[Jan Beulich <jbeulich@xxxxxxxx>]

On 13.03.2025 17:05, Jürgen Groß wrote:
> On 13.03.25 16:54, Jan Beulich wrote:
>> On 11.03.2025 21:59, Julien Grall wrote:
>>> On 05/03/2025 09:11, Mykola Kvach wrote:
>>>> Invocation of the CPU_UP_PREPARE notification
>>>> on ARM64 during resume causes a crash:
>>>>
>>>> (XEN) [  315.807606] Error bringing CPU1 up: -16
>>>> (XEN) [  315.811926] Xen BUG at common/cpu.c:258
>>>> [...]
>>>> (XEN) [  316.142765] Xen call trace:
>>>> (XEN) [  316.146048]    [<00000a0000202264>] 
>>>> enable_nonboot_cpus+0x128/0x1ac (PC)
>>>> (XEN) [  316.153219]    [<00000a000020225c>] 
>>>> enable_nonboot_cpus+0x120/0x1ac (LR)
>>>> (XEN) [  316.160391]    [<00000a0000278180>] 
>>>> suspend.c#system_suspend+0x4c/0x1a0
>>>> (XEN) [  316.167476]    [<00000a0000206b70>] 
>>>> domain.c#continue_hypercall_tasklet_handler+0x54/0xd0
>>>> (XEN) [  316.176117]    [<00000a0000226538>] 
>>>> tasklet.c#do_tasklet_work+0xb8/0x100
>>>> (XEN) [  316.183288]    [<00000a0000226920>] do_tasklet+0x68/0xb0
>>>> (XEN) [  316.189077]    [<00000a000026e120>] domain.c#idle_loop+0x7c/0x194
>>>> (XEN) [  316.195644]    [<00000a0000277638>] 
>>>> shutdown.c#halt_this_cpu+0/0x14
>>>> (XEN) [  316.202383]    [<0000000000000008>] 0000000000000008
>>>>
>>>> Freeing per-CPU areas and setting __per_cpu_offset to INVALID_PERCPU_AREA
>>>> only occur when !park_offline_cpus and system_state is not 
>>>> SYS_STATE_suspend.
>>>> On ARM64, park_offline_cpus is always false, so setting __per_cpu_offset to
>>>> INVALID_PERCPU_AREA depends solely on the system state.
>>>>
>>>> If the system is suspended, this area is not freed, and during resume, an 
>>>> error
>>>> occurs in init_percpu_area, causing a crash because INVALID_PERCPU_AREA is 
>>>> not
>>>> set and park_offline_cpus remains 0:
>>>>
>>>>       if ( __per_cpu_offset[cpu] != INVALID_PERCPU_AREA )
>>>>           return park_offline_cpus ? 0 : -EBUSY;
>>>>
>>>> It appears that the same crash can occur on x86 if park_offline_cpus is set
>>>> to 0 during Xen suspend.
>>>
>>> I am rather confused. Looking at the x86 code, it seems
>>> park_offline_cpus is cleared for AMD platforms. So are you saying the
>>> suspend/resume doesn't work on AMD?
>>
>> Right now I can't see how it would work there. I've asked Marek for 
>> clarification
>> as to their users using S3 only on Intel hardware.
> 
> Seems as if this issue has been introduced with commit f75780d26b2f
> ("xen: move per-cpu area management into common code"). Before that
> on x86 there was just:
> 
>      if ( __per_cpu_offset[cpu] != INVALID_PERCPU_AREA )
>          return 0;
> 
> in init_percpu_area().

Ah yes. Mykola, can you then please address this by adjusting 
init_percpu_area(),
adding a Fixes: tag to reference the commit above?

Looking at the tags of the patch, please also make sure you clarify who's the
original author of the patch. Your S-o-b isn't first, but there's also no From:.

Jan