Re: [PATCH v10 1/4] xen/arm: Implement PSCI SYSTEM_SUSPEND call for guests

[Jan Beulich <jbeulich@xxxxxxxx>]

On 27.08.2025 23:21, Mykola Kvach wrote:
> --- a/xen/common/domain.c
> +++ b/xen/common/domain.c
> @@ -1349,16 +1349,10 @@ int domain_shutdown(struct domain *d, u8 reason)
>      return 0;
>  }
>  
> -void domain_resume(struct domain *d)
> +static void domain_resume_nopause(struct domain *d)
>  {
>      struct vcpu *v;
>  
> -    /*
> -     * Some code paths assume that shutdown status does not get reset under
> -     * their feet (e.g., some assertions make this assumption).
> -     */
> -    domain_pause(d);
> -
>      spin_lock(&d->shutdown_lock);
>  
>      d->is_shutting_down = d->is_shut_down = 0;
> @@ -1366,13 +1360,40 @@ void domain_resume(struct domain *d)
>  
>      for_each_vcpu ( d, v )
>      {
> +        /*
> +         * No need to conditionally clear _VPF_suspended here:
> +         * - This bit is only set on Arm, and only after a successful 
> suspend.

How likely do you think it is that, if e.g. RISC-V or PPC clone Arm's
code, this comment would then be updated accordingly? IOW I don't think
a justification like this one should be written in such terms.

> +         * - domain_resume_nopause() may also be called from paths other than
> +         *   the suspend/resume flow, such as "soft-reset" actions (e.g.,
> +         *   on_poweroff), as part of the Xenstore control/shutdown protocol.
> +         *   These require guest acknowledgement to complete the operation.

I'm having trouble connecting "require guest acknowledgement" to ...

> +         * So clearing the bit unconditionally is safe.

... the safety of the unconditional clearing.

> +         */
> +        clear_bit(_VPF_suspended, &v->pause_flags);
> +
>          if ( v->paused_for_shutdown )
>              vcpu_unpause(v);
>          v->paused_for_shutdown = 0;
>      }
>  
>      spin_unlock(&d->shutdown_lock);
> +}
>  
> +#ifdef CONFIG_ARM
> +void domain_resume_nopause_helper(struct domain *d)

This is an odd name to use from code meaning to invoke domain_resume_nopause().
Why isn't this called domain_resume_nopause(), and ...

> +{
> +    domain_resume_nopause(d);

... the static function simply _domain_resume_nopause() (in full accordance
to the C standard's naming rules)?

> +}
> +#endif
> +
> +void domain_resume(struct domain *d)
> +{
> +    /*
> +     * Some code paths assume that shutdown status does not get reset under
> +     * their feet (e.g., some assertions make this assumption).
> +     */
> +    domain_pause(d);

As you move the comment - no such assumptions exist when the code path
through domain_resume_nopause_helper() is taken?

Jan