Re: [Xen-devel] [PATCHv1] xen/balloon: disable memory hotplug in PV guests

[David Vrabel <david.vrabel@xxxxxxxxxx>]

On 09/03/15 15:25, Boris Ostrovsky wrote:
> On 03/09/2015 11:13 AM, David Vrabel wrote:
>> On 09/03/15 15:09, Boris Ostrovsky wrote:
>>> On 03/09/2015 10:10 AM, David Vrabel wrote:
>>>> Memory hotplug doesn't work with PV guests because:
>>>>
>>>>     a) The p2m cannot be expanded to cover the new sections.
>>>>
>>>>     b) add_memory() builds page tables for the new sections which means
>>>>        the new pages must have valid p2m entries (or a BUG occurs).
>>> Is this due to recent p2m rework?
>> (a) is but (b) has always meant memory hotplug on PV was broken.
> 
> I can see why (b) should probably have prevented it from working but I
> tried this on 4.4/3.17 and that seemed to work (it indeed does not
> function well on newer bits).

I tried it on 3.10 (+ some other bits and pieces) and it was definitely
broken for reason (b).  I had to refactor the balloon driver to populate
the sections before calling add_memory() before it would work.  But this
can't be done now because of (a).

David

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