Re: [Xen-devel] Design doc of adding ACPI support for arm64 on Xen - version 2

[Christoffer Dall <christoffer.dall@xxxxxxxxxx>]

On Wed, Aug 12, 2015 at 5:45 PM, Jan Beulich <JBeulich@xxxxxxxx> wrote:
>>>> On 07.08.15 at 04:11, <zhaoshenglong@xxxxxxxxxx> wrote:
>> 1. Copy and change some EFI and ACPI tables
>> -------------------------------------------
>
> A key thing I'm missing here is reasoning of why this copying approach
> is needed in the first place. Remember that on the x86 side we get
> away without any such copying-and-changing. Yet the farther you
> diverge from x86's model, the more changes you'll need to common
> Xen code in e.g. Linux.
>
>> All these tables will be copied to Dom0 memory except that the reused
>> tables(DSDT, SPCR, etc) will be mapped to Dom0.
>
> Which again seems odd - such tables should be considered MMIO
> (despite living in RAM), and hence not be part of Dom0's memory
> assignment.
>
not sure if this applies to the context of your comment, but we had
issues before when trying to deal with this data as device memory
(MMIO), because ARM doesn't allow unaligned accesses etc. on device
memory, and so Dom0 would crash at memory abort exceptions during
boot, so this really does have to be mapped as RAM to Dom0.  If you
meant some internal Xen bookkeeping thing, then just ignore me.

-Christoffer

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