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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 13.09.12 at 17:17, Keir Fraser <keir.xen@xxxxxxxxx> wrote:
> 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.
> :)

Agreed.

Jan


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