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

["Zhang, Yang Z" <yang.z.zhang@xxxxxxxxx>]

Jan Beulich wrote on 2014-09-25:
>>>> On 25.09.14 at 04:30, <yang.z.zhang@xxxxxxxxx> wrote:
>> Jan Beulich wrote on 2014-09-24:
>>>>>> On 24.09.14 at 10:53, <tiejun.chen@xxxxxxxxx> wrote:
>>>> On 2014/9/24 16:47, Jan Beulich wrote:
>>>>>>>> On 24.09.14 at 10:35, <tiejun.chen@xxxxxxxxx> wrote:
>>>>>> In tools stack, how can we get ultimate e820 table built by hvmloader?
>>>>> 
>>>>> What is this needed for?
>>>> 
>>>> I mean in case of a hotplug after the migration, we should check
>>>> any overlap with current existing RAM/MMIO, right? So we need to
>>>> know current existing guest RAM/MMIO layout since this ultimate
>>>> e820 table is just built by hvmloader, not in xen internal.
>>> 
>>> Actually I think we'd be better off not complicating the tool stack
>>> for this - with proper checking for collisions in the P2M updates,
>>> the assignment ought to fail without the tool stack doing anything.
>> 
>> 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.

> 
> Jan


Best regards,
Yang



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