[ 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.
