Re: [PATCH v6 01/23] xen: introduce CONFIG_HAS_SHARED_INFO for archs without a shared page

[Jan Beulich <jbeulich@xxxxxxxx>]

On 20.07.2026 17:59, Oleksii Kurochko wrote:
> --- a/xen/common/domctl.c
> +++ b/xen/common/domctl.c
> @@ -102,9 +102,14 @@ void getdomaininfo(struct domain *d, struct 
> xen_domctl_getdomaininfo *info)
>  #ifdef CONFIG_MEM_PAGING
>      info->paged_pages       = atomic_read(&d->paged_pages);
>  #endif
> -    info->shared_info_frame =
> -        gfn_x(mfn_to_gfn(d, _mfn(virt_to_mfn(d->shared_info))));
> -    BUG_ON(SHARED_M2P(info->shared_info_frame));
> +    if ( IS_ENABLED(CONFIG_HAS_SHARED_INFO) )
> +    {
> +        info->shared_info_frame =
> +            gfn_x(mfn_to_gfn(d, _mfn(virt_to_mfn(d->shared_info))));
> +        BUG_ON(SHARED_M2P(info->shared_info_frame));
> +    }
> +    else
> +        info->shared_info_frame = gfn_x(INVALID_GFN);

There's one issue left here: INVALID_GFN is a Xen internal concept. It could
change value if we saw a need. Therefore you cannot use that value here, to
supply it as hypercall output. It needs to be ~0, and imo the public header
also wants amending to indicate the special meaning of this value.

And there's one further aspect to consider: Do we really want to retain the
shared_info struct domain field when !HAS_SHARED_INFO? Making it conditional
would require some adjustment here, but might be tidier overall. In
particular doing so would eliminate the risk of new uses of the field
appearing, with people not noticing that they'd break RISC-V.

Jan