Re: [PATCH] xen: introduce XENFEAT_direct_mapped and XENFEAT_not_direct_mapped

[Jan Beulich <jbeulich@xxxxxxxx>]

On 25.02.2021 02:22, Stefano Stabellini wrote:
> --- a/xen/include/public/features.h
> +++ b/xen/include/public/features.h
> @@ -114,6 +114,13 @@
>   */
>  #define XENFEAT_linux_rsdp_unrestricted   15
>  
> +/*
> + * A direct-mapped (or 1:1 mapped) domain is a domain for which its
> + * local pages have gfn == mfn.
> + */
> +#define XENFEAT_not_direct_mapped       16
> +#define XENFEAT_direct_mapped           17

Why two new values? Absence of XENFEAT_direct_mapped requires
implying not-direct-mapped by the consumer anyway, doesn't it?

Further, quoting xen/mm.h: "For a non-translated guest which
is aware of Xen, gfn == mfn." This to me implies that PV would
need to get XENFEAT_direct_mapped set; not sure whether this
simply means x86'es is_domain_direct_mapped() is wrong, but if
it is, uses elsewhere in the code would likely need changing.

Also, nit: Please keep the right sides aligned with #define-s
higher up in the file.

Jan