Re: [PATCH v2 04/17] xen/arm: xc_domain_ioport_permission(..) not supported on ARM.

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Wed, 22 Sep 2021, Rahul Singh wrote:
> ARM architecture does not implement I/O ports. Ignore this call on ARM
> to avoid the overhead of making a hypercall just for Xen to return
> -ENOSYS.
> 
> Signed-off-by: Rahul Singh <rahul.singh@xxxxxxx>
> ---
> Change in v2:
> - Instead of returning success in XEN, ignored the call in xl.
> ---
>  tools/libs/ctrl/xc_domain.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/tools/libs/ctrl/xc_domain.c b/tools/libs/ctrl/xc_domain.c
> index 23322b70b5..25c95f6596 100644
> --- a/tools/libs/ctrl/xc_domain.c
> +++ b/tools/libs/ctrl/xc_domain.c
> @@ -1348,6 +1348,14 @@ int xc_domain_ioport_permission(xc_interface *xch,
>                                  uint32_t nr_ports,
>                                  uint32_t allow_access)
>  {
> +#if defined(__arm__) || defined(__aarch64__)
> +    /*
> +     * The ARM architecture does not implement I/O ports.
> +     * Avoid the overhead of making a hypercall just for Xen to return 
> -ENOSYS.
> +     * It is safe to ignore this call on ARM so we just return 0.
> +     */
> +    return 0;

I think this is fine from a code change point of view.

I wonder if we want to return 0 or return an error here, but I am
thinking that 0 is OK because there is really nothing to do anyway as
they end up ignored one way or the other.

Based on that reasoning:

Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>


> +#else
>      DECLARE_DOMCTL;
>  
>      domctl.cmd = XEN_DOMCTL_ioport_permission;
> @@ -1357,6 +1365,7 @@ int xc_domain_ioport_permission(xc_interface *xch,
>      domctl.u.ioport_permission.allow_access = allow_access;
>  
>      return do_domctl(xch, &domctl);
> +#endif
>  }
>  
>  int xc_availheap(xc_interface *xch,
> -- 
> 2.17.1
> 
>