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

["Egger, Christoph" <chegger@xxxxxxxxx>]

On 2015/01/13 21:45, Andrew Cooper wrote:
> On 13/01/15 20:02, Ed White wrote:
>> On 01/13/2015 11:01 AM, Andrew Cooper wrote:
>>
>>> I can't think of any reasonable case where the alternate p2m would want
>>> mappings different to the host p2m.  That is to say, an altp2m will map
>>> the same set of mfns to make a guest physical address space, but may
>>> differ in page permissions and possibly p2m types.
>>>
>> 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 can imagine to reduce overhead for PV frontend/backend driver
communication by saying the "mfn" is dom0's "gmfn".

Christoph


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