Re: [Xen-devel] [PATCH] include/public: add new elf note for support of huge physical addresses

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 14.08.17 at 12:21, <jgross@xxxxxxxx> wrote:
> Current pv guests will only see physical addresses up to 46 bits wide.
> In order to be able to run on a host supporting 5 level paging and to
> make use of any possible memory page there, physical addresses with up
> to 52 bits have to be supported.

Is this a Xen shortcoming or a Linux one (I assume the latter)?

> --- a/xen/include/public/elfnote.h
> +++ b/xen/include/public/elfnote.h
> @@ -212,9 +212,18 @@
>  #define XEN_ELFNOTE_PHYS32_ENTRY 18
>  
>  /*
> + * Maximum physical address size the kernel can handle.
> + *
> + * All memory of the PV guest must be allocated below this boundary,
> + * as the guest kernel can't handle page table entries with MFNs referring
> + * to memory above this value.
> + */
> +#define XEN_ELFNOTE_MAXPHYS_SIZE 19

Without use in the hypervisor or tools I don't see what good
introducing this note will do.

Jan


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