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

[Julien Grall <julien.grall@xxxxxxxxxx>]

On 11/08/15 15:59, Ian Campbell wrote:
> On Tue, 2015-08-11 at 15:51 +0100, David Vrabel wrote:
>> On 11/08/15 15:12, Ian Campbell wrote:
>>> On Fri, 2015-08-07 at 10:11 +0800, Shannon Zhao wrote:
>>>>
>>> [...]
>>>> 3. Dom0 gets grant table and event channel irq information
>>>> -----------------------------------------------------------
>>>> As said above, we assign the hypervisor_id be "XenVMM" to tell Dom0 
>>>> that
>>>> it runs on Xen hypervisor.
>>>>
>>>> For grant table, add two new HVM_PARAMs: 
>>>> HVM_PARAM_GNTTAB_START_ADDRESS
>>>> and HVM_PARAM_GNTTAB_SIZE.
>>>
>>> The reason we expose this range is essentially to allow OS authors to 
>>> take
>>> a short cut by telling them about an IPA range which is unused, so it 
>>> is
>>> available for remapping the grant table into. On x86 there is a BAR on 
>>> the
>>> Xen platform PCI device which serves a similar purpose.
>>>
>>> IIRC somebody (perhaps David V, CCd) had proposed at some point to make 
>>> it
>>> so that Linux was able to pick such an IPA itself by examining the 
>>> memory
>>> map or by some other scheme.
>>
>> PVH in Linux uses ballooned pages which are vmap()'d into a virtually
>> contiguous region.
>>
>> See xlated_setup_gnttab_pages().
> 
> So somewhat more concrete than a proposal then ;-)
> 
> I don't see anything there which would be a problem on ARM, so we should
> probably go that route there too (at least for ACPI, if not globally for
> all ARM guests).

IIRC we talked about it few months ago and you said that using balloon
page will split in 4K the 1G/2M mapping done in the stage-2 p2m.

Note that for DOM0 we never give back the ballooned page to Xen. This is
because we have to respect the 1:1 mapping when DOM0 want to get back
the page.

Regards,

-- 
Julien Grall

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel