[PATCH v6.12.y] selftests/mm: hugepage-mremap: fix mapping alignment

[Luiz Capitulino <luizcap@redhat.com>]

commit a914785f6349da754e1226420bf4e51961956769 upstream.

When running the HugeTLB kselftest suite on arm64 with 64K base pages,
this test always fails:

  # -------------------------
  # running ./hugepage-mremap
  # -------------------------
  # TAP version 13
  # 1..1
  # # Map haddr: Returned address is 0x7eaa40000000
  # # Map daddr: Returned address is 0x7daa40000000
  # # Map vaddr: Returned address is 0x7faa40000000
  # Bail out! ioctl-UFFDIO_REGISTER: Invalid argument
  # # Planned tests != run tests (1 != 0)
  # # Totals: pass:0 fail:0 xfail:0 xpass:0 skip:0 error:0
  # [FAIL]
  not ok 1 hugepage-mremap # exit=1
  # NOTE: These hugetlb tests provide minimal coverage.  Use
  #       https://github.com/libhugetlbfs/libhugetlbfs.git for
  #       hugetlb regression testing.
  # SKIP ./uffd-wp-mremap

The problem is that the default HugeTLB page size on such systems is
512 MiB and 'length' is not aligned to the page size. This causes
uffd_register() to fail as 'length' is 10 MiB and not aligned to the
HugeTLB page size.

On upstream this was fixed by a914785f6349 ("selftests/mm: hugetlb-mremap:
add setup of HugeTLB pages") as that commit aligns 'length' to the
default HugeTLB page size as part of what it's doing. Since this commit
is part of a 50+ patch series, we backport only the 'length' alignment
bits to fix the test.

Signed-off-by: Luiz Capitulino <luizcap@redhat.com>
---
 tools/testing/selftests/mm/hugepage-mremap.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/tools/testing/selftests/mm/hugepage-mremap.c b/tools/testing/selftests/mm/hugepage-mremap.c
index 3070484f9ed0..42dd4eeba52b 100644
--- a/tools/testing/selftests/mm/hugepage-mremap.c
+++ b/tools/testing/selftests/mm/hugepage-mremap.c
@@ -87,6 +87,7 @@ static void register_region_with_uffd(char *addr, size_t len)
 
 int main(int argc, char *argv[])
 {
+	unsigned long hugepage_size;
 	size_t length = 0;
 	int ret = 0, fd;
 
@@ -104,7 +105,12 @@ int main(int argc, char *argv[])
 	else
 		length = DEFAULT_LENGTH_MB;
 
+	hugepage_size = default_huge_page_size();
+	if (!hugepage_size)
+		ksft_exit_skip("Could not detect default hugetlb page size\n");
+
 	length = MB_TO_BYTES(length);
+	length = (length + hugepage_size - 1) & ~(hugepage_size - 1);
 	fd = memfd_create(argv[0], MFD_HUGETLB);
 	if (fd < 0)
 		ksft_exit_fail_msg("Open failed: %s\n", strerror(errno));
-- 
2.55.0