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

[Daniel Kiper <daniel.kiper@xxxxxxxxxx>]

On Mon, Mar 09, 2015 at 11:25:07AM -0400, 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).

It was introduced in Linux Kernel 3.1 and it worked on PV, HVM and maybe
on PVHVM but I am not sure. IIRC, I tested this stuff on Xen 4.0 or 4.1.

Daniel

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