Re: [Xen-devel] [PATCH] public/elfnote: document non-alignment of relocated init-P2M

[Juergen Gross <jgross@xxxxxxxx>]

On 09/05/17 17:06, Jan Beulich wrote:
>>>> On 09.05.17 at 16:36, <jgross@xxxxxxxx> wrote:
>> On 09/05/17 16:23, Jan Beulich wrote:
>>> Since PV kernels can't use large pages anywa, when the init-P2M support
>>> was added it was decided to keep the implementation simple and not
>>> align large pages in PFN space. Document this.
>>>
>>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>>>
>>> --- a/xen/include/public/elfnote.h
>>> +++ b/xen/include/public/elfnote.h
>>> @@ -173,7 +173,9 @@
>>>   * The (non-default) location the initial phys-to-machine map should be
>>>   * placed at by the hypervisor (Dom0) or the tools (DomU).
>>>   * The kernel must be prepared for this mapping to be established using
>>> - * large pages, despite such otherwise not being available to guests.
>>> + * large pages, despite such otherwise not being available to guests. Note
>>
>> Shouldn't the large page usage be limited to dom0?
> 
> Why? Even if the tools right now don't use large pages here, why
> should we preclude them wanting to at some point?

Those could be of temporary nature only in order not to break migration.
So the guest would be forced to split the big pages up anyway. Why
create them in the beginning then?


Juergen


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