Re: [PATCH v2 0/2] mm: Memory offlining + page isolation cleanups

[Michal Hocko]

On Tue 22-10-19 11:17:24, David Hildenbrand wrote:
> On 22.10.19 11:14, Michal Hocko wrote:
> > On Tue 22-10-19 10:32:11, David Hildenbrand wrote:
> > [...]
> > > E.g., arch/x86/kvm/mmu.c:kvm_is_mmio_pfn()
> > 
> > Thanks for these references. I am not really familiar with kvm so I
> > cannot really comment on the specific code but I am wondering why
> > it simply doesn't check for ZONE_DEVICE explicitly? Also we do care
> > about holes in RAM (from the early boot), those should be reserved
> > already AFAIR. So we are left with hotplugged memory with holes and
> > I am not really sure we should bother with this until there is a clear
> > usecase in sight.
> 
> Well, checking for ZONE_DEVICE is only possible if you have an initialized
> memmap. And that is not guaranteed when you start mapping random stuff into
> your guest via /dev/mem.

Yes, I can understand that part but checking PageReserved on an
uninitialized memmap is pointless as well. So if you can test for it you
can very well test for ZONE_DEVICE as well. PageReserved -> ZONE_DEVICE
is a terrible assumption.

> I am reworking these patches right now and audit the whole kernel for
> PageReserved() checks that might affect ZONE_DEVICE. I'll send the
> collection of patches as RFC.

Thanks a lot!
-- 
Michal Hocko
SUSE Labs