Re: [Xen-devel] [Patch V2] expand x86 arch_shared_info to support linear p2m list

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 01.12.14 at 10:29, <JGross@xxxxxxxx> wrote:
> The x86 struct arch_shared_info field pfn_to_mfn_frame_list_list
> currently contains the mfn of the top level page frame of the 3 level
> p2m tree, which is used by the Xen tools during saving and restoring
> (and live migration) of pv domains and for crash dump analysis. With
> three levels of the p2m tree it is possible to support up to 512 GB of
> RAM for a 64 bit pv domain.
> 
> A 32 bit pv domain can support more, as each memory page can hold 1024
> instead of 512 entries, leading to a limit of 4 TB.
> 
> To be able to support more RAM on x86-64 switch to a virtual mapped
> p2m list.
> 
> This patch expands struct arch_shared_info with a new p2m list virtual
> address, the root of the page table root and a p2m generation count.
> The new information is indicated by the domain to be valid by storing
> ~0UL into pfn_to_mfn_frame_list_list. The hypervisor indicates
> usability of this feature by a new flag XENFEAT_virtual_p2m.
> 
> Right now XENFEAT_virtual_p2m will not be set. This will change when
> the Xen tools support the virtual mapped p2m list.

This seems wrong: XENFEAT_* only reflect hypervisor capabilities.
I.e. the availability of the new functionality may need to be
advertised another way - xenstore perhaps?

Jan


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