Re: [PATCH v2 0/5] Allocate memmap from hotadded memory

From: Michal Hocko
Date: Thu Aug 01 2019 - 03:40:12 EST

On Thu 01-08-19 09:31:09, David Hildenbrand wrote:
> On 01.08.19 09:26, David Hildenbrand wrote:
> > I am not sure about the implications of having
> > pfn_valid()/pfn_present()/pfn_online() return true but accessing it
> > results in crashes. (suspend, kdump, whatever other technology touches
> > online memory)
> (oneidea: we could of course go ahead and mark the pages PG_offline
> before unmapping the pfn range to work around these issues)

PG_reserved and an elevated reference count should be enough to drive
any pfn walker out. Pfn walkers shouldn't touch any page unless they
know and recognize their type.
Michal Hocko