Re: [Xen-devel] [PATCH 3/4 RFC] x86/p2m: use large pages for MMIO mappings

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 29.09.15 at 15:06, <julien.grall@xxxxxxxxxx> wrote:
> On 29/09/15 14:00, Jan Beulich wrote:
>>>>> On 29.09.15 at 14:52, <julien.grall@xxxxxxxxxx> wrote:
>>> On 29/09/15 13:46, Jan Beulich wrote:
>>>> Again, make map_mmio_regions() a wrapper around an ARM-specific
>>>> function with the extra argument. No need to alter common or x86
>>>> code.
>>>
>>> TBH, extending the mapp_mmio_region is the best solution.
>>>
>>> The name map_mmio_region is very generic and there is no reason we can't
>>> use it in the hypervisor. Adding yet another wrapper will confuse people
>>> and it will be hard for both the reviewer and the developer to know
>>> which one to use.
>> 
>> I disagree - the function was originally meant to exclusively support
>> the respective domctl. The fact that ARM gained (many) more uses
>> should not impact common code or x86.
> 
> The expectation you described is neither documented nor explicit from
> the name...

From history only, agreed.

> As the interface is not set in stone, we could decide to extend the
> usage of the function to make a coherent interface and not adding new
> wrapper because we don't want to touch x86...

One more thing - what meaning would you expect the new parameter
to carry? Number of frames mapped? Number of iterations done? In
the former case, the goal aimed at here won't be achievable. In the
latter case, would you mean to pass -1UL for it for the ARM callers
wanting the operation to run to completion?

Jan


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