Re: [PATCH v2 3/5] mm: Teach pfn_to_online_page() about ZONE_DEVICE section collisions
From: Oscar Salvador <osalvador@suse.de>
Date: 2021-01-12 11:01:29
Also in:
lkml, nvdimm
On Tue, Jan 12, 2021 at 01:34:53AM -0800, Dan Williams wrote:
While pfn_to_online_page() is able to determine pfn_valid() at
subsection granularity it is not able to reliably determine if a given
pfn is also online if the section is mixes ZONE_{NORMAL,MOVABLE} with
ZONE_DEVICE. This means that pfn_to_online_page() may return invalid
@page objects. For example with a memory map like:
100000000-1fbffffff : System RAM
142000000-143002e16 : Kernel code
143200000-143713fff : Kernel rodata
143800000-143b15b7f : Kernel data
144227000-144ffffff : Kernel bss
1fc000000-2fbffffff : Persistent Memory (legacy)
1fc000000-2fbffffff : namespace0.0
This command:
echo 0x1fc000000 > /sys/devices/system/memory/soft_offline_page
...succeeds when it should fail. When it succeeds it touches
an uninitialized page and may crash or cause other damage (see
dissolve_free_huge_page()).[...]
Because the collision case is rare, and for simplicity, the
SECTION_TAINT_ZONE_DEVICE flag is never cleared once set.
Fixes: ba72b4c8cf60 ("mm/sparsemem: support sub-section hotplug")
Cc: Andrew Morton <akpm@linux-foundation.org>
Reported-by: Michal Hocko <mhocko@suse.com>
Reported-by: David Hildenbrand <redacted>
Signed-off-by: Dan Williams <redacted>Reviewed-by: Oscar Salvador <osalvador@suse.de> -- Oscar Salvador SUSE L3