Re: [Xen-devel] [PATCH] x86/mm: remove the linear mapping of the p2m tables

[Keir Fraser <keir.xen@xxxxxxxxx>]

On 13/09/2012 16:08, "Jan Beulich" <JBeulich@xxxxxxxx> wrote:

>>>> On 13.09.12 at 16:58, Keir Fraser <keir.xen@xxxxxxxxx> wrote:
>> On 13/09/2012 15:42, "Tim Deegan" <tim@xxxxxxx> wrote:
>> 
>>>> Is that also going to remain true when we won't be able to 1:1-
>>>> map all of the memory anymore once we break the current 5Tb
>>>> barrier? If not, it would probably be worthwhile keeping that
>>>> code.
>>> 
>>> Ah, 5TB is a smaller limit than I thought we had.  Yes, better leave it
>>> alone, so.  Though TBH finding some way to use a bit more virtual
>>> address space for Xen seems like a good idea anyway, since this won't be
>>> the only place we'll want to avoid TLB flushes.
>> 
>> For HVM or PVH guests, where this HAP code would be used, clearly Xen can
>> use all the virtual address space it wants. It will almost certainly make
>> sense for Xen to have a 1:1 physical mapping of all memory when running such
>> a guest, and only do mapcache type tricks when running legacy PV guests.
> 
> Yes, that's the mode I indeed wanted to get to. Just that it's
> not really clear to me (without having started at least the
> work of bumping the boundary) how intrusive those changes
> are going to be.

Well, this is true. But almost regardless of the complexity, this is how
we're going to want to do it, and it does mean we won't need the linear map.
:)

 -- Keir

> Jan
> 



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