On 17.09.19 04:34, Toshiki Fukasawa wrote: > On 2019/09/09 16:46, David Hildenbrand wrote: >> Let's take a step back here to understand the issues I am aware of. I >> think we should solve this for good now: >> >> A PFN walker takes a look at a random PFN at a random point in time. It >> finds a PFN with SECTION_MARKED_PRESENT && !SECTION_IS_ONLINE. The >> options are: >> >> 1. It is buddy memory (add_memory()) that has not been online yet. The >> memmap contains garbage. Don't access. >> >> 2. It is ZONE_DEVICE memory with a valid memmap. Access it. >> >> 3. It is ZONE_DEVICE memory with an invalid memmap, because the section >> is only partially present: E.g., device starts at offset 64MB within a >> section or the device ends at offset 64MB within a section. Don't access it. > > I don't agree with case #3. In the case, struct page area is not allocated on > ZONE_DEVICE, but is allocated on system memory. So I think we can access the > struct pages. What do you mean "invalid memmap"? No, that's not the case. There is no memory, especially not system memory. We only allow partially present sections (sub-section memory hotplug) for ZONE_DEVICE. invalid memmap == memmap was not initialized == struct pages contains garbage. There is a memmap, but accessing it (e.g., pfn_to_nid()) will trigger a BUG. -- Thanks, David / dhildenb
