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

[Julien Grall <julien.grall@citrix.com>]

Hi Parth,

On 14/06/2015 11:27, Parth Dixit wrote:
> On 8 June 2015 at 22:20, Julien Grall <julien.grall@citrix.com> wrote:
>> Hi Parth,
>>
>> On 17/05/2015 21:03, Parth Dixit wrote:
>>>
>>> In ACPI mmio regions are described in DSDT which requires
>>> AML interpreter. Defer the mapping of mmio until DSDT is parsed in
>>> DOM0 and map mmio's dynamically at the time of request.
>>
>>
>> I'm against a such solution. Even though it's DOM0 we should avoid to allow
>> him to map anything (RAM,...) on data abort.
> I think we agreed to this solution
> http://lists.xenproject.org/archives/html/xen-devel/2015-06/msg02059.html

Firstly, this kind of link should have been put in the changelog of the 
patch (after ---). It helps the reviewer to know what was decided (or 
not) on the previous discussion. It's more true with a series of more 
than 40 patches...

Secondly, the thread you pointed as some discussion on it but no formal 
agreement about what to do. If there is no answer, it's better to do a 
resume and ask if anyone are agree.

Finally, what you've implemented and what was suggested by Ian is 
different. You are allowing any region to be mapped in DOM0 via this 
way. Only MMIO should be allowed.

Concerning the mapping attribute used. Based on Ard answer "The UEFI 
spec mandates that the memory map describes all memory in the system, so 
if dom0 accesses any ranges outside of that, it makes sense
to just use device mappings for stage 2.". We should use by default 
Device Stage 2, it's safer. If it doesn't work later (because some PCI 
BAR may be memory, which if I wasn't able to prove), then we can think 
differently.

For the mapping of the MMIO to DOM0, I believe we can map any non-RAM 
(and any non-RAM not used by Xen) regions to DOM0 at boot time (I think 
x86 does that). It would keep the ACPI code contained at boot time and 
no difference during runtime.

Regards,

-- 
Julien Grall