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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 29.09.15 at 14:16, <julien.grall@xxxxxxxxxx> wrote:
> On 29/09/15 12:44, Jan Beulich wrote:
>>>>> On 29.09.15 at 13:33, <julien.grall@xxxxxxxxxx> wrote:
>>> On 15/09/15 08:34, Jan Beulich wrote:
>>>> RFC reasons:
>>>> - ARM side unimplemented (and hence libxc for now made cope with both
>>>>   models), the main issue (besides my inability to test any change
>>>>   there) being the many internal uses of map_mmio_regions())
>>>
>>> map_mmio_regions is used in ARM to map all the device memory in a guest.
>>> We expect this function to map everything at once when called during
>>> DOM0 build and/or when a guest is created (used to map the interrupt
>>> controller).
>>>
>>> I would rather prefer to avoid introducing specific helpers with
>>> slightly different behavior (i.e one is only mapping N page, the other
>>> everything).
>>>
>>> What about extending map_mmio_regions to take a parameter telling if we
>>> want to limit the number of mapping in a single invocation?
>> 
>> Sure an option, albeit something that would be sufficient to be
>> done in ARM specific code, albeit the only user using variable
>> length is map_range_to_domain(). All the others, using fixed
>> lengths up to 32 pages, would implicitly get everything done at
>> once as long as the threshold is >= 32.
> 
> While this is the case today, we have different patch series coming up
> using variable lenght in different place within the ARM code (vGIC,
> ACPI...).

Okay.

> It won't be possible to use map_range_to_domain because it's very
> specific to build DOM0.

Sure; I didn't even think of suggesting that.

> So, I would extend map_mmio_region like that
> 
> map_mmio_regions(struct domain *d,
>                unsigned long start_gfn,
>                unsigned long nr,
>                unsigned long mfn,
>                unsigned long limit);
> 
> The limit parameter would be 0 if there is no limit otherwise the
> maximum of iteration.

Again, make map_mmio_regions() a wrapper around an ARM-specific
function with the extra argument. No need to alter common or x86
code.

Jan


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel