[PATCH v2 0/5] mm/vmalloc: make the mapping functions undo their partial mappings

[Hao Ge <hao.ge@linux.dev>]

__vmap_pages_range_noflush() and friends can install some PTEs before
failing and leave them mapped, and the kernel callers do not agree on
who cleans them up. pcpu_map_pages() and kmsan_ioremap_page_range()
roll back what they mapped before the failure, while
vm_module_tags_populate() and the __GFP_NOFAIL retry loop in
__vmalloc_area_node() rely on the mapping functions cleaning up and
do not call anything like vunmap_range() themselves. When the same
range is mapped again, the attempt hits the leftovers and fails, with
a BUG() in vmap_pte_range() for huge mappings and a warning on the
small-page path.

After discussing with Suren and Ulad [1], we move the rollback into the
mapping functions. A failed vmap leaves nothing mapped, and the
callers no longer clean up after it.

[1] https://lore.kernel.org/all/20260915070001.113559-3-hao.ge@linux.dev/

Patch 1 is the KMSAN part. The shadow and the origin of a range
are mapped by two separate calls, so the rollback there has to
cover both. Patch 2 is its disabled-KMSAN counterpart. Patch 3 adds
the rollback to __vmap_pages_range_noflush() and vmap_page_range().
Patches 4 and 5 drop the powerpc and percpu cleanups that are not
needed anymore.

Changes since v1:
 - Add patch 2. Sashiko reported that an empty range that hits patch 3's
   WARN_ON_ONCE() trips __vunmap_range_noflush()'s BUG_ON() through
   kmsan_vunmap_range_noflush() when kmsan=0. Patch 2 adds the
   kmsan_enabled check the unmap side was missing.
 - Pick up Reviewed-by tags from Suren and Ulad on patches 1, 4 and 5.
 - Add Cc: stable to patch 3.

v1 link: https://lore.kernel.org/all/20261009063619.112313-1-hao.ge@linux.dev/

Hao Ge (5):
  mm/kmsan: undo the shadow mapping when the origin mapping fails
  mm/kmsan: skip vunmap_range_noflush when KMSAN is disabled
  mm/vmalloc: undo partial mappings inside the mapping functions
  powerpc: drop redundant unmaps of failed vmap mappings
  mm/percpu: stop unmapping the CPU that failed to map

 arch/powerpc/kernel/isa-bridge.c |  5 ++--
 arch/powerpc/kernel/pci_64.c     |  4 +--
 mm/kmsan/hooks.c                 |  3 +++
 mm/kmsan/shadow.c                |  4 +++
 mm/percpu-vm.c                   |  5 ++--
 mm/vmalloc.c                     | 44 +++++++++++++++++++++++---------
 6 files changed, 45 insertions(+), 20 deletions(-)

-- 
2.25.1