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Re: [Xen-devel] [v6][PATCH 2/2] xen:vtd: missing RMRR mapping while share EPT

>>> On 26.09.14 at 03:24, <yang.z.zhang@xxxxxxxxx> wrote:
> Jan Beulich wrote on 2014-09-25:
>>>>> On 25.09.14 at 04:30, <yang.z.zhang@xxxxxxxxx> wrote:
>>> How do the checking in P2M updates? Only hvmloader knows whether the
>>> RMRR region is reserved. If we want do the check in hypervisor, we
>>> need to report those info to hypervisor.
>> First of all the hypervisor has the information - it is where the
>> information comes from that tools and hvmloader consume. And then the
>> check will need to be a collision check: If while establishing an
>> identity mapping another mapping is found to be already in place, the
>> request will need to be failed. And similarly if a "normal" mapping
>> request finds a 1:1 mapping already in place, this ought to result in
>> failure too. Of course a prerequisite to this is that error get properly 
> bubbled up through all layers.
> If there is another mapping already there and it is different from the one 
> we are establishing, we should return failure. But if the existing mapping is 
> same to the one we are establishing, how we can know whether it is a 'normal 
> memory 1:1' mapping or it is created by previous operation of RMRR 
> creating(e.g. there already a device with RMRR assigned to this guest). What 
> I am thinking is that we need a flag to know whether the mapping is RMRR 
> mapping or regular memory mapping.

If the new and old mappings are the same, nothing needs to be done
at all (as is already the case in one direction in the patches we have
seen). And yes, for the case when there is an occasional 1:1 mapping
we of course will need some way of identifying intentional ones.


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