[PATCH] selftests/mm: run_vmtests.sh: fix half_ufd_size_MB calculation

[Rafael Aquini <aquini@redhat.com>]

From: Rafael Aquini <raquini@redhat.com>

We noticed that uffd-stress test was always failing to run when invoked
for the hugetlb profiles on x86_64 systems with a processor count of 64
or bigger:
  ...
  # ------------------------------------
  # running ./uffd-stress hugetlb 128 32
  # ------------------------------------
  # ERROR: invalid MiB (errno=9, @uffd-stress.c:459)
  ...
  # [FAIL]
  not ok 3 uffd-stress hugetlb 128 32 # exit=1
  ...

The problem boils down to how run_vmtests.sh (mis)calculates the size
of the region it feeds to uffd-stress. The latter expects to see an
amount of MiB while the former is just giving out the number of free
hugepages halved down. This measurement discrepancy ends up violating
uffd-stress' assertion on number of hugetlb pages allocated per CPU,
causing it to bail out with the error above.

This commit fixes that issue by adjusting run_vmtests.sh's half_ufd_size_MB
calculation so it properly renders the region size in MiB, as expected,
while maintaining all of its original constraints in place.

Fixes: 2e47a445d7b3 ("selftests/mm: run_vmtests.sh: fix hugetlb mem size calculation")
Signed-off-by: Rafael Aquini <raquini@redhat.com>
---
 tools/testing/selftests/mm/run_vmtests.sh | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/mm/run_vmtests.sh b/tools/testing/selftests/mm/run_vmtests.sh
index 333c468c2699..157d07e5aaa3 100755
--- a/tools/testing/selftests/mm/run_vmtests.sh
+++ b/tools/testing/selftests/mm/run_vmtests.sh
@@ -304,7 +304,9 @@ uffd_stress_bin=./uffd-stress
 CATEGORY="userfaultfd" run_test ${uffd_stress_bin} anon 20 16
 # Hugetlb tests require source and destination huge pages. Pass in half
 # the size of the free pages we have, which is used for *each*.
-half_ufd_size_MB=$((freepgs / 2))
+# uffd-stress expects a region expressed in MiB, so we adjust
+# half_ufd_size_MB accordingly.
+half_ufd_size_MB=$(((freepgs * hpgsize_KB) / 1024 / 2))
 CATEGORY="userfaultfd" run_test ${uffd_stress_bin} hugetlb "$half_ufd_size_MB" 32
 CATEGORY="userfaultfd" run_test ${uffd_stress_bin} hugetlb-private "$half_ufd_size_MB" 32
 CATEGORY="userfaultfd" run_test ${uffd_stress_bin} shmem 20 16
-- 
2.47.0