[PATCH v3 0/4] memblock, arm: fixes for freeing of the memory map

[Mike Rapoport]

From: Mike Rapoport <rppt@xxxxxxxxxxxxx>

Hi,

The coordination between freeing of unused memory map, pfn_valid() and core
mm assumptions about validity of the memory map in various ranges was not
designed for complex layouts of the physical memory with a lot of holes all
over the place.

Kefen Wang reported crashes in move_freepages() on a system with the
following memory layout [1]:

  node   0: [mem 0x0000000080a00000-0x00000000855fffff]
  node   0: [mem 0x0000000086a00000-0x0000000087dfffff]
  node   0: [mem 0x000000008bd00000-0x000000008c4fffff]
  node   0: [mem 0x000000008e300000-0x000000008ecfffff]
  node   0: [mem 0x0000000090d00000-0x00000000bfffffff]
  node   0: [mem 0x00000000cc000000-0x00000000dc9fffff]
  node   0: [mem 0x00000000de700000-0x00000000de9fffff]
  node   0: [mem 0x00000000e0800000-0x00000000e0bfffff]
  node   0: [mem 0x00000000f4b00000-0x00000000f6ffffff]
  node   0: [mem 0x00000000fda00000-0x00000000ffffefff]

The crashes can be mitigated by enabling CONFIG_HOLES_IN_ZONE and
essentially turning pfn_valid_within() to pfn_valid() instead of having it
hardwired to 1, but this would require to keep CONFIG_HOLES_IN_ZONE which
could be removed after arm64 and MIPS stopped using it ([2], [3]).

Alternatively, we can update ARM's implementation of pfn_valid() to take
into accounting rounding of the freed memory map to pageblock boundaries
and make sure it returns true for PFNs that have memory map entries even if
there is no physical memory.

I'm planning to merge this via memblock tree.

v3: 
* Add patch 3/4 to ensure there is no overflow in memblock_overlaps_region()

v2: Link: https://lore.kernel.org/lkml/20210519141436.11961-1-rppt@xxxxxxxxxx
* Use single memblock_overlaps_region() instead of several
  memblock_is_map_memory() lookups. This makes this series depend on update
  of MEMBLOCK_NOMAP handling in the memory map [2]

v1: Link: https://lore.kernel.org/lkml/20210518090613.21519-1-rppt@xxxxxxxxxx

[1] https://lore.kernel.org/lkml/2a1592ad-bc9d-4664-fd19-f7448a37edc0@xxxxxxxxxx
[2] https://lore.kernel.org/lkml/20210511100550.28178-1-rppt@xxxxxxxxxx
[3] https://lore.kernel.org/lkml/20210418093512.668-1-rppt@xxxxxxxxxx

Mike Rapoport (4):
  memblock: free_unused_memmap: use pageblock units instead of MAX_ORDER
  memblock: align freed memory map on pageblock boundaries with SPARSEMEM
  memblock: ensure there is no overflow in memblock_overlaps_region()
  arm: extend pfn_valid to take into account freed memory map alignment

 arch/arm/mm/init.c | 13 ++++++++++++-
 mm/memblock.c      | 26 ++++++++++++++------------
 2 files changed, 26 insertions(+), 13 deletions(-)


base-commit: c4681547bcce777daf576925a966ffa824edd09d
-- 
2.28.0