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

[David Hildenbrand]

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.

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,

David / dhildenb