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

On 13/08/15 11:54, Jan Beulich wrote:
>>>> On 13.08.15 at 12:48, <zhaoshenglong@xxxxxxxxxx> wrote:
>> On 2015/8/13 18:29, Christoffer Dall wrote:
>>> However, what about for other resources?  Having code somewhere that
>>> says "hide this random piece of hardware if you're Xen dom0" sounds
>>> awful to me.  I know it's only the serial port right now, but still.
>> It needs to modify MADT table according to dom0_max_vcpus and modify EFI
>> MMAP table according to dom0_mem. And modify FADT table to set
>> hypervisor_id as "XenVMM" to tell Dom0 that it runs on Xen hypervisor.
> None of this should be required:
> Unaltered MADT may (or should I say will) be needed to drive P- or
> C-states.

We have to alter MADT for different reasons:
        - restricting the number of vCPUs
        - update the CPU bring up method
        - changing the CPUID

Maybe we should pass a backup but we don't support cpufreq driver right
now and it would need quite a look of work to do it (see [1]).

> UEFI memmap shouldn't be exposed to Dom0 at all.

We have to craft a UEFI memmap in order to notify Dom0 where are the RAM

> Detecting running on Xen should (hopefully) be possible by other
> means for Dom0.

How there is no cpuid like on ARM. So no possibility to know whether you
are running on Xen or another hypervisor...

Modifying the FADT is the only viable solution we have today in order to
tell that it's running on Xen.



Julien Grall

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