Re: [PATCH v2] xen/percpu: don't initialize percpu on resume

[Mykola Kvach <xakep.amatop@xxxxxxxxx>]

On Thu, Mar 27, 2025 at 1:32 PM Mykola Kvach <xakep.amatop@xxxxxxxxx> wrote:
>

Hmm, looks like this line...

> From: Mykola Kvach <mykola_kvach@xxxxxxxx>

...shouldn't be here

>
> 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;
>
> The same crash can occur on x86 if park_offline_cpus is set
> to 0 during Xen resume.
>
> Fixes: f75780d26b2f ("xen: move per-cpu area management into common code")
> Signed-off-by: Mykyta Poturai <mykyta_poturai@xxxxxxxx>
> Signed-off-by: Mykola Kvach <mykola_kvach@xxxxxxxx>
> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
> ---
> Changes introduced in V2:
>  - cosmetic fixes after review
>  - chnages in a commit message: add "Fixes"
> ---
>  xen/common/percpu.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/xen/common/percpu.c b/xen/common/percpu.c
> index e4e8b7bcab..b20f0460fc 100644
> --- a/xen/common/percpu.c
> +++ b/xen/common/percpu.c
> @@ -30,7 +30,9 @@ static int init_percpu_area(unsigned int cpu)
>      char *p;
>
>      if ( __per_cpu_offset[cpu] != INVALID_PERCPU_AREA )
> -        return park_offline_cpus ? 0 : -EBUSY;
> +        return park_offline_cpus || system_state == SYS_STATE_resume
> +            ? 0
> +            : -EBUSY;
>
>      if ( (p = alloc_xenheap_pages(PERCPU_ORDER, 0)) == NULL )
>          return -ENOMEM;
> --
> 2.43.0
>