Re: [Xen-devel] [PATCH 00/11] Alternate p2m: support multiple copies of host p2m

["Jan Beulich" <jbeulich@xxxxxxxx>]

>>> Ed White <edmund.h.white@xxxxxxxxx> 01/13/15 10:32 PM >>>
>On 01/13/2015 12:45 PM, Andrew Cooper wrote:
>> On 13/01/15 20:02, Ed White wrote:
>>> The set of mfn's is the same, but I do allow gfn->mfn mappings to be
>>> modified under certain circumstances. One use of this is to point the
>>> same VA to different physical pages (with different access permissions)
>>> in different p2m's to hide memory changes.
>> 
>> What is the practical use of being able to play paging tricks like this
>> behind a VMs back?
> 
>I'm restricted in how much detail I can go into on a public mailing list,
>but imagine that you want a data read to see one thing and an instruction
>fetch to see something else.

How would that work? There can only be one P2M in use at a time, and that's
used for both translations. Or are you saying at least one of the two accesses
would be emulated nevertheless?

Jan


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