On Thu, Jun 21, 2018 at 11:08 PM, Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx> wrote: > Reading /proc/kpageflags for pfns allocated by pmem namespace triggers > kernel panic with a message like "BUG: unable to handle kernel paging > request at fffffffffffffffe". > > The first few pages (controlled by altmap passed to memmap_init_zone()) > in the ZONE_DEVICE can skip struct page initialization, which causes > the reported issue. > > This patch simply adds some initialization code for them. > > Fixes: 4b94ffdc4163 ("x86, mm: introduce vmem_altmap to augment vmemmap_populate()") > Signed-off-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx> > --- > mm/page_alloc.c | 10 +++++++++- > 1 file changed, 9 insertions(+), 1 deletion(-) > > diff --git v4.17-mmotm-2018-06-07-16-59/mm/page_alloc.c v4.17-mmotm-2018-06-07-16-59_patched/mm/page_alloc.c > index 1772513..0b36afe 100644 > --- v4.17-mmotm-2018-06-07-16-59/mm/page_alloc.c > +++ v4.17-mmotm-2018-06-07-16-59_patched/mm/page_alloc.c > @@ -5574,8 +5574,16 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone, > * Honor reservation requested by the driver for this ZONE_DEVICE > * memory > */ > - if (altmap && start_pfn == altmap->base_pfn) > + if (altmap && start_pfn == altmap->base_pfn) { > + unsigned long i; > + > + for (i = 0; i < altmap->reserve; i++) { > + page = pfn_to_page(start_pfn + i); > + __init_single_page(page, start_pfn + i, zone, nid); > + SetPageReserved(page); > + } > start_pfn += altmap->reserve; > + } No, unfortunately this will clobber metadata that lives in that reserved area, see __nvdimm_setup_pfn().