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

[Keir Fraser <keir.xen@gmail.com>]

On 13/09/2012 16:11, "Tim Deegan" <tim@xen.org> wrote:

> At 15:58 +0100 on 13 Sep (1347551914), Keir Fraser wrote:
>> On 13/09/2012 15:42, "Tim Deegan" <tim@xen.org> 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.
> 
> This is also used for shadowed guests, including autotranslated PV
> guests, if anyone cares about them any more.  I got the impression that
> they're superseded by the pvh stuff; is that right?

Auto-translated PV seems to be one of those unsupported things that never
quite dies. With PVH just round the corner, let's definitively call it dead.
:)

> If that's the case, then let's commit to having a bigger 1-1 map on HVM
> guetst when the time comes to extend past 5TB, and remove this linear
> map after all. 

I agree.

 -- Keir

> Tim.