From: Qian Cai cai@lca.pw Subject: mm/page_owner: don't access uninitialized memmaps when reading /proc/pagetypeinfo

Uninitialized memmaps contain garbage and in the worst case trigger kernel BUGs, especially with CONFIG_PAGE_POISONING. They should not get touched.

For example, when not onlining a memory block that is spanned by a zone and reading /proc/pagetypeinfo with CONFIG_DEBUG_VM_PGFLAGS and CONFIG_PAGE_POISONING, we can trigger a kernel BUG:

:/# echo 1 > /sys/devices/system/memory/memory40/online :/# echo 1 > /sys/devices/system/memory/memory42/online :/# cat /proc/pagetypeinfo > test.file [ 42.489856] page:fffff2c585200000 is uninitialized and poisoned [ 42.489861] raw: ffffffffffffffff ffffffffffffffff ffffffffffffffff ffffffffffffffff [ 42.492235] raw: ffffffffffffffff ffffffffffffffff ffffffffffffffff ffffffffffffffff [ 42.493501] page dumped because: VM_BUG_ON_PAGE(PagePoisoned(p)) [ 42.494533] There is not page extension available. [ 42.495358] ------------[ cut here ]------------ [ 42.496163] kernel BUG at include/linux/mm.h:1107! [ 42.497069] invalid opcode: 0000 [#1] SMP NOPTI

Please note that this change does not affect ZONE_DEVICE, because pagetypeinfo_showmixedcount_print() is called from mm/vmstat.c:pagetypeinfo_showmixedcount() only for populated zones, and ZONE_DEVICE is never populated (zone->present_pages always 0).

[david@redhat.com: move check to outer loop, add comment, rephrase description] Link: http://lkml.kernel.org/r/20191011140638.8160-1-david@redhat.com Fixes: f1dd2cd13c4b ("mm, memory_hotplug: do not associate hotadded memory to zones until online") # visible after d0dc12e86b319 Signed-off-by: Qian Cai cai@lca.pw Signed-off-by: David Hildenbrand david@redhat.com Acked-by: Michal Hocko mhocko@suse.com Acked-by: Vlastimil Babka vbabka@suse.cz Cc: Thomas Gleixner tglx@linutronix.de Cc: "Peter Zijlstra (Intel)" peterz@infradead.org Cc: Miles Chen miles.chen@mediatek.com Cc: Mike Rapoport rppt@linux.vnet.ibm.com Cc: Qian Cai cai@lca.pw Cc: Greg Kroah-Hartman gregkh@linuxfoundation.org Cc: stable@vger.kernel.org [4.13+] Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/page_owner.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/mm/page_owner.c~mm-page_owner-dont-access-uninitialized-memmaps-when-reading-proc-pagetypeinfo +++ a/mm/page_owner.c @@ -271,7 +271,8 @@ void pagetypeinfo_showmixedcount_print(s * not matter as the mixed block count will still be correct */ for (; pfn < end_pfn; ) { - if (!pfn_valid(pfn)) { + page = pfn_to_online_page(pfn); + if (!page) { pfn = ALIGN(pfn + 1, MAX_ORDER_NR_PAGES); continue; } @@ -279,13 +280,13 @@ void pagetypeinfo_showmixedcount_print(s block_end_pfn = ALIGN(pfn + 1, pageblock_nr_pages); block_end_pfn = min(block_end_pfn, end_pfn);

- page = pfn_to_page(pfn); pageblock_mt = get_pageblock_migratetype(page);

for (; pfn < block_end_pfn; pfn++) { if (!pfn_valid_within(pfn)) continue;

+ /* The pageblock is online, no need to recheck. */ page = pfn_to_page(pfn);

if (page_zone(page) != zone) _