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Re: [Xen-devel] [PATCH v2 32/41] arm : acpi dynamically map mmio regions

Hi Shannon,

On 31/07/15 02:30, Shannon Zhao wrote:
> On 2015/7/31 2:31, Julien Grall wrote:
>> On 30/07/15 19:02, Parth Dixit wrote:
>>>                     instead of getting mmio information for individual
>>> devices from dsdt, we will map all the non-ram regions described in
>>> uefi. AML interpreter option was discussed earlier and it was decided
>>> not to go with that approach. You can find more details in the linaro
>>> xen wiki for the reasoning behind it.
>> Which page are you talking about? I only found [1] speaking about ACPI.
>> Although, there is nothing related to MMIO mapping.
>> Anyway, it's not possible to get the list of MMIOs regions for the UEFI
>> System Memory Map (see the mail you forward on the ML [2]).
>> Although, based on the RAM region we could deduce a possible set of MMIO
>> regions.
> But I guess this will get the all regions except RAM region. And some of
> the regions may not exist on hardware. Is it ok to map the non-exist
> region to DOM0? Doesn't the map function fail?

I don't see a problem for it. I'm not sure what the others think about it.

The map function doesn't know if the physical region is valid or not.
It's only setup the page table to allow the guest using the physical region.

If DOM0 is trying to access invalid region, it will receive a
data/prefetch abort.

>> It would be fine to mapped unused region in memory and we could
>> take advantage of super page.
>> While you are speaking about the wiki page. Can one of you update the
>> wiki page about the boot protocol? Jan had some concerns about the
>> solution you choose (see [3] to not mention the whole thread).
> About the XENV table, from the discussions of the thread, it seems we
> reach an agreement on using hypercall to tell DOM0 the grant table info
> and event channel irq. Right?

People have different opinion on what should be the way to boot DOM0
with ACPI on ARM. A design document would help here to understand what
are the possibilities to boot DOM0 (i.e hypercall based, XENV...) and
which one would be the most suitable for ARM.

>> We need to agree on the boot protocol before going further on this series.
>> To speed up the upstreaming process, it would be nice if you start a
>> thread about the boot protocol for ACPI with relevant people in CCed.
>> The main goal will be to explain why you choose this way. This will be
>> the base to talk about improvement and/or answer concerns for other people.
> Ok, it's good to reach an agreement before action.
>> FWIW, Jan also suggested a different boot protocol based on the x86 one.
>> It may be good for you to see whether it would fit ACPI on ARM.
> Which boot protocol? Could you point it out? Thanks. :)

The way to boot DOM0 with ACPI. There is a page on the Linaro wiki [1],
but the content is quite out of date now.


[1] https://wiki.linaro.org/LEG/Engineering/Virtualization/ACPI_on_Xen

Julien Grall

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