selftests/mm: fix division-by-zero in uffd-unit-tests

Commit 4dfd4bba8578 ("selftests/mm/uffd: refactor non-composite global
vars into struct") moved some of the operations previously implemented in
uffd_setup_environment() earlier in the main test loop.

The calculation of nr_pages, which involves a division by page_size, now
occurs before checking that default_huge_page_size() returns a non-zero
This leads to a division-by-zero error on systems with !CONFIG_HUGETLB.

Fix this by relocating the non-zero page_size check before the nr_pages
calculation, as it was originally implemented.

Link: https://lkml.kernel.org/r/20251113034623.3127012-1-cmllamas@google.com
Fixes: 4dfd4bba8578 ("selftests/mm/uffd: refactor non-composite global vars into struct")
Signed-off-by: Carlos Llamas <cmllamas@google.com>
Acked-by: David Hildenbrand (Red Hat) <david@kernel.org>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Reviewed-by: Ujwal Kundur <ujwal.kundur@gmail.com>
Cc: Brendan Jackman <jackmanb@google.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/tools/testing/selftests/mm/uffd-unit-tests.c b/tools/testing/selftests/mm/uffd-unit-tests.c
index 9e3be2ee7f1ba4f6c6f465c3b718457f365ef7d2..f917b4c4c9436915ea21226066da7a68eb8f8aa5 100644 (file)
--- a/tools/testing/selftests/mm/uffd-unit-tests.c
+++ b/tools/testing/selftests/mm/uffd-unit-tests.c
@@ -1758,10 +1758,15 @@ int main(int argc, char *argv[])
                        uffd_test_ops = mem_type->mem_ops;
                        uffd_test_case_ops = test->test_case_ops;
 
-                       if (mem_type->mem_flag & (MEM_HUGETLB_PRIVATE | MEM_HUGETLB))
+                       if (mem_type->mem_flag & (MEM_HUGETLB_PRIVATE | MEM_HUGETLB)) {
                                gopts.page_size = default_huge_page_size();
-                       else
+                               if (gopts.page_size == 0) {
+                                       uffd_test_skip("huge page size is 0, feature missing?");
+                                       continue;
+                               }
+                       } else {
                                gopts.page_size = psize();
+                       }
 
                        /* Ensure we have at least 2 pages */
                        gopts.nr_pages = MAX(UFFD_TEST_MEM_SIZE, gopts.page_size * 2)
@@ -1776,12 +1781,6 @@ int main(int argc, char *argv[])
                                continue;
 
                        uffd_test_start("%s on %s", test->name, mem_type->name);
-                       if ((mem_type->mem_flag == MEM_HUGETLB ||
-                           mem_type->mem_flag == MEM_HUGETLB_PRIVATE) &&
-                           (default_huge_page_size() == 0)) {
-                               uffd_test_skip("huge page size is 0, feature missing?");
-                               continue;
-                       }
                        if (!uffd_feature_supported(test)) {
                                uffd_test_skip("feature missing");
                                continue;