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

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Mon, Mar 09, 2015 at 03:31:30PM +0000, David Vrabel wrote:
> 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).

That should really be reflected in the commit description (the a) part).
> 
> David

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