Re: [PATCH v2 15/26] xen/domctl: wrap xsm_{irq_permission,iomem_permission} with CONFIG_MGMT_HYPERCALLS

[Jan Beulich <jbeulich@xxxxxxxx>]

On 10.09.2025 09:38, Penny Zheng wrote:
> @@ -508,13 +510,21 @@ static inline int xsm_unbind_pt_irq(
>  static inline int xsm_irq_permission(
>      xsm_default_t def, struct domain *d, int pirq, uint8_t allow)
>  {
> +#ifdef CONFIG_MGMT_HYPERCALLS
>      return alternative_call(xsm_ops.irq_permission, d, pirq, allow);
> +#else
> +    return -EOPNOTSUPP;
> +#endif
>  }
>  
>  static inline int xsm_iomem_permission(
>      xsm_default_t def, struct domain *d, uint64_t s, uint64_t e, uint8_t 
> allow)
>  {
> +#ifdef CONFIG_MGMT_HYPERCALLS
>      return alternative_call(xsm_ops.iomem_permission, d, s, e, allow);
> +#else
> +    return -EOPNOTSUPP;
> +#endif
>  }

Along the lines of Stefano's comment - why would these inline functions stay
around? Them returning an error in the MGMT_HYPERCALLS=n case is actually a
problem: For xsm_iomem_permission() it's only a conceptual one, but for
xsm_irq_permission() you break x86's handling of XEN_DOMCTL_gsi_permission.
I would have added "transiently", but from the titles of later patches I
can't spot where to expect that one to be taken care of.

> --- a/xen/xsm/flask/hooks.c
> +++ b/xen/xsm/flask/hooks.c
> @@ -1111,12 +1111,14 @@ static int cf_check flask_unbind_pt_irq(
>      return current_has_perm(d, SECCLASS_RESOURCE, RESOURCE__REMOVE);
>  }
>  
> +#ifdef CONFIG_MGMT_HYPERCALLS
>  static int cf_check flask_irq_permission(
>      struct domain *d, int pirq, uint8_t access)
>  {
>      /* the PIRQ number is not useful; real IRQ is checked during mapping */
>      return current_has_perm(d, SECCLASS_RESOURCE, resource_to_perm(access));
>  }
> +#endif /* CONFIG_MGMT_HYPERCALLS */
>  
>  struct iomem_has_perm_data {
>      uint32_t ssid;
> @@ -1943,8 +1945,10 @@ static const struct xsm_ops __initconst_cf_clobber 
> flask_ops = {
>      .unmap_domain_irq = flask_unmap_domain_irq,
>      .bind_pt_irq = flask_bind_pt_irq,
>      .unbind_pt_irq = flask_unbind_pt_irq,
> +#ifdef CONFIG_MGMT_HYPERCALLS
>      .irq_permission = flask_irq_permission,
>      .iomem_permission = flask_iomem_permission,
> +#endif
>      .iomem_mapping = flask_iomem_mapping,
>      .pci_config_permission = flask_pci_config_permission,
>  

It's odd that flask_iomem_permission() remains as a function, but for the
moment that looks to be necessary, as it's (oddly enough) called from
flask_iomem_mapping(). However, for that one I again can't drive from
titles of subsequent patches where it would be taken care of.

Daniel - is this layering actually helpful? Can't we either drop
flask_iomem_mapping() (with the benefit of a cf_check disappearing), or
have it do directly what it wants done, rather than calling the other
hook function?

Having reached the bottom of the patch - what about xsm/dummy.h?

Jan