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


  • To: Mykola Kvach <xakep.amatop@xxxxxxxxx>
  • From: Jan Beulich <jbeulich@xxxxxxxx>
  • Date: Thu, 28 Aug 2025 09:40:26 +0200
  • Autocrypt: addr=jbeulich@xxxxxxxx; keydata= xsDiBFk3nEQRBADAEaSw6zC/EJkiwGPXbWtPxl2xCdSoeepS07jW8UgcHNurfHvUzogEq5xk hu507c3BarVjyWCJOylMNR98Yd8VqD9UfmX0Hb8/BrA+Hl6/DB/eqGptrf4BSRwcZQM32aZK 7Pj2XbGWIUrZrd70x1eAP9QE3P79Y2oLrsCgbZJfEwCgvz9JjGmQqQkRiTVzlZVCJYcyGGsD /0tbFCzD2h20ahe8rC1gbb3K3qk+LpBtvjBu1RY9drYk0NymiGbJWZgab6t1jM7sk2vuf0Py O9Hf9XBmK0uE9IgMaiCpc32XV9oASz6UJebwkX+zF2jG5I1BfnO9g7KlotcA/v5ClMjgo6Gl MDY4HxoSRu3i1cqqSDtVlt+AOVBJBACrZcnHAUSuCXBPy0jOlBhxPqRWv6ND4c9PH1xjQ3NP nxJuMBS8rnNg22uyfAgmBKNLpLgAGVRMZGaGoJObGf72s6TeIqKJo/LtggAS9qAUiuKVnygo 3wjfkS9A3DRO+SpU7JqWdsveeIQyeyEJ/8PTowmSQLakF+3fote9ybzd880fSmFuIEJldWxp Y2ggPGpiZXVsaWNoQHN1c2UuY29tPsJgBBMRAgAgBQJZN5xEAhsDBgsJCAcDAgQVAggDBBYC AwECHgECF4AACgkQoDSui/t3IH4J+wCfQ5jHdEjCRHj23O/5ttg9r9OIruwAn3103WUITZee e7Sbg12UgcQ5lv7SzsFNBFk3nEQQCACCuTjCjFOUdi5Nm244F+78kLghRcin/awv+IrTcIWF hUpSs1Y91iQQ7KItirz5uwCPlwejSJDQJLIS+QtJHaXDXeV6NI0Uef1hP20+y8qydDiVkv6l IreXjTb7DvksRgJNvCkWtYnlS3mYvQ9NzS9PhyALWbXnH6sIJd2O9lKS1Mrfq+y0IXCP10eS FFGg+Av3IQeFatkJAyju0PPthyTqxSI4lZYuJVPknzgaeuJv/2NccrPvmeDg6Coe7ZIeQ8Yj t0ARxu2xytAkkLCel1Lz1WLmwLstV30g80nkgZf/wr+/BXJW/oIvRlonUkxv+IbBM3dX2OV8 AmRv1ySWPTP7AAMFB/9PQK/VtlNUJvg8GXj9ootzrteGfVZVVT4XBJkfwBcpC/XcPzldjv+3 HYudvpdNK3lLujXeA5fLOH+Z/G9WBc5pFVSMocI71I8bT8lIAzreg0WvkWg5V2WZsUMlnDL9 mpwIGFhlbM3gfDMs7MPMu8YQRFVdUvtSpaAs8OFfGQ0ia3LGZcjA6Ik2+xcqscEJzNH+qh8V m5jjp28yZgaqTaRbg3M/+MTbMpicpZuqF4rnB0AQD12/3BNWDR6bmh+EkYSMcEIpQmBM51qM EKYTQGybRCjpnKHGOxG0rfFY1085mBDZCH5Kx0cl0HVJuQKC+dV2ZY5AqjcKwAxpE75MLFkr wkkEGBECAAkFAlk3nEQCGwwACgkQoDSui/t3IH7nnwCfcJWUDUFKdCsBH/E5d+0ZnMQi+G0A nAuWpQkjM1ASeQwSHEeAWPgskBQL
  • Cc: Mykola Kvach <mykola_kvach@xxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
  • Delivery-date: Thu, 28 Aug 2025 07:40:33 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

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



 


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