Re: [Xen-devel] Design doc of adding ACPI support for arm64 on Xen - version 5

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 02.09.15 at 15:48, <julien.grall@xxxxxxxxxx> wrote:
> On 02/09/15 14:26, Ian Campbell wrote:
>>>>> I think the problem is how you reserved this region in the EFI memory
>>>>> table. From what I saw, you marked this new memory with EFI_MEMORY_WB
>>>>> (which means that the region can be usable by Linux).
>>>>>
>>>> Yes, I mark it with EFI_MEMORY_WB. Is this right?
>>>
>>> I would say no, but it's only because I looked at the kernel code 
>>> quickly.
>>>
>>> You have to looks how ACPI region/UEFI tables are described in the host
>>> EFI memory map and mimicking for the DOM0 EFI memory map.
>> 
>> Surely it is the type (EfiACPIReclaimMemory, EfiACPIMemoryNVS etc) and not
>> the mapping attributes which should control whether an OS considers a
>> region usable? At least until the OS is done parsing tables neither of
>> those are usable (which implies we want NVS as our type, unless the memory
>> is intended to be reclaimed by dom0, implying it should own it).
> 
> It looks like that Linux on ARM64 is considering any region with
> EFI_MEMORY_WB set as normal RAM and will try to add as System RAM (see
> reserve_regions in arch/arm64/kernel/efi.c).

This should be corrected, as it's certainly not in line with the spec.

Jan


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