[PATCH v1 0/3] Improve hugetlbfs read on HWPOISON hugepages

[Jiaqi Yan <jiaqiyan@google.com>]

Today when hardware memory is corrupted in a hugetlb hugepage,
kernel leaves the hugepage in pagecache [1]; otherwise future mmap or
read will suject to silent data corruption. This is implemented by
returning -EIO from hugetlb_read_iter immediately if the hugepage has
HWPOISON flag set.

Since memory_failure already tracks the raw HWPOISON subpages in a
hugepage, a natural improvement is possible: if userspace only asks for
healthy subpages in the pagecache, kernel can return these data.

This patchset implements this improvement. It consist of three parts.
The 1st commit exports the functionality to tell if a subpage inside a
hugetlb hugepage is a raw HWPOISON page. The 2nd commit teaches
hugetlbfs_read_iter to return as many healthy bytes as possible.
The 3rd commit properly tests this new feature.

[1] commit 8625147cafaa ("hugetlbfs: don't delete error page from pagecache")

Jiaqi Yan (3):
  mm/hwpoison: find subpage in hugetlb HWPOISON list
  hugetlbfs: improve read HWPOISON hugepage
  selftests/mm: add tests for HWPOISON hugetlbfs read

 fs/hugetlbfs/inode.c                          |  62 +++-
 include/linux/mm.h                            |  23 ++
 mm/memory-failure.c                           |  26 +-
 tools/testing/selftests/mm/.gitignore         |   1 +
 tools/testing/selftests/mm/Makefile           |   1 +
 .../selftests/mm/hugetlb-read-hwpoison.c      | 322 ++++++++++++++++++
 6 files changed, 419 insertions(+), 16 deletions(-)
 create mode 100644 tools/testing/selftests/mm/hugetlb-read-hwpoison.c

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2.40.1.606.ga4b1b128d6-goog