Re: [Xen-devel] [PATCH 1/4] expand x86 arch_shared_info to support linear p2m list

[Juergen Gross <jgross@xxxxxxxx>]

On 11/14/2014 12:41 PM, Andrew Cooper wrote:
> On 14/11/14 09:37, Juergen Gross 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 and the mfn of the page table root. 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.
> How do you envisage this being used?  Are you expecting the tools to do
> manual pagetable walks using xc_map_foreign_xxx() ?
Yes. Not very different compared to today's mapping via the 3 level
p2m tree. Just another entry format, 4 instead of 3 levels and starting
at an offset.


Juergen


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