Dan Williams <dan.j.williams@xxxxxxxxx> writes: > [ add Alistair ] > > Peter Xu wrote: >> Not all pages may apply to pgtable check. One example is ZONE_DEVICE >> pages: they map PFNs directly, and they don't allocate page_ext at all even >> if there's struct page around. One may reference devm_memremap_pages(). >> >> When both ZONE_DEVICE and page-table-check enabled, then try to map some >> dax memories, one can trigger kernel bug constantly now when the kernel was >> trying to inject some pfn maps on the dax device: >> >> kernel BUG at mm/page_table_check.c:55! >> >> While it's pretty legal to use set_pxx_at() for ZONE_DEVICE pages for page >> fault resolutions, skip all the checks if page_ext doesn't even exist in >> pgtable checker, which applies to ZONE_DEVICE but maybe more. > > This looks correct to me, and needed in the near term. You can add: > > Reviewed-by: Dan Williams <dan.j.williams@xxxxxxxxx> > > In the long term, the page_ext check may not be needed. I.e. the reason > I added Alistair was in case his work to make DAX pages behave like > typical pages for reference counting would also make them behave the > same for the presence of page_ext. It doesn't currently. However I did run into this bug while I was developing those so please add: Reviewed-by: Alistair Popple <apopple@xxxxxxxxxx>
