Re: [PATCH v4 1/4] xen: XENMEM_exchange should only be used/compiled for arch supporting PV guest

[Jan Beulich <jbeulich@xxxxxxxx>]

On 21.09.2020 20:02, Julien Grall wrote:
> --- a/xen/common/memory.c
> +++ b/xen/common/memory.c
> @@ -504,6 +504,7 @@ static bool propagate_node(unsigned int xmf, unsigned int 
> *memflags)
>  
>  static long memory_exchange(XEN_GUEST_HANDLE_PARAM(xen_memory_exchange_t) 
> arg)
>  {
> +#ifdef CONFIG_PV
>      struct xen_memory_exchange exch;
>      PAGE_LIST_HEAD(in_chunk_list);
>      PAGE_LIST_HEAD(out_chunk_list);
> @@ -516,6 +517,9 @@ static long 
> memory_exchange(XEN_GUEST_HANDLE_PARAM(xen_memory_exchange_t) arg)
>      struct domain *d;
>      struct page_info *page;
>  
> +    if ( !is_pv_domain(d) )
> +        return -EOPNOTSUPP;

I think "paging_mode_translate(d)" would be more correct, at which
point the use later in the function ought to be dropped (as that's
precisely one of the things making this function not really
sensible to use on translated guests).

I also wonder whether the #ifdef wouldn't better be left out. Yes,
that'll mean retaining a stub mfn_to_gmfn(), but it could expand
to simply BUG() then, for example.

Jan