[PATCH v2 08/13] selftests/mm: ensure destination is hugetlb-backed in hugepage-mremap

[Sayali Patil <sayalip@linux.ibm.com>]

The hugepage-mremap selftest reserves the destination address using a
anonymous base-page mapping before calling mremap() with MREMAP_FIXED,
while the source region is hugetlb-backed.

When remapping a hugetlb mapping into a base-page VMA may fail with:

    mremap: Device or resource busy

This is observed on powerpc hash MMU systems where slice constraints
and page size incompatibilities prevent the remap.

Ensure the destination region is created using MAP_HUGETLB so that both
source and destination VMAs are hugetlb-backed and compatible. Also add
MAP_POPULATE to the destination mapping to prefault hugepages,
matching the behaviour used for other hugetlb mapping in the test and
ensuring deterministic behaviour.

Update the FLAGS macro to include MAP_HUGETLB | MAP_SHARED |
MAP_POPULATE so that both mappings are hugetlb-backed and compatible.
Also use the macro for the mmap() calls to avoid repeating
the flag combination.

This ensures the test reliably exercises hugetlb mremap instead of
failing due to VMA type mismatch.

Fixes: 12b613206474 ("mm, hugepages: add hugetlb vma mremap() test")
Acked-by: Zi Yan <ziy@nvidia.com>
Signed-off-by: Sayali Patil <sayalip@linux.ibm.com>
---
 tools/testing/selftests/mm/hugepage-mremap.c | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/tools/testing/selftests/mm/hugepage-mremap.c b/tools/testing/selftests/mm/hugepage-mremap.c
index e611249080d6..48c24a4ba9a7 100644
--- a/tools/testing/selftests/mm/hugepage-mremap.c
+++ b/tools/testing/selftests/mm/hugepage-mremap.c
@@ -31,7 +31,7 @@
 #define MB_TO_BYTES(x) (x * 1024 * 1024)
 
 #define PROTECTION (PROT_READ | PROT_WRITE | PROT_EXEC)
-#define FLAGS (MAP_SHARED | MAP_ANONYMOUS)
+#define FLAGS (MAP_HUGETLB | MAP_SHARED | MAP_POPULATE)
 
 static void check_bytes(char *addr)
 {
@@ -121,23 +121,20 @@ int main(int argc, char *argv[])
 
 	/* mmap to a PUD aligned address to hopefully trigger pmd sharing. */
 	unsigned long suggested_addr = 0x7eaa40000000;
-	void *haddr = mmap((void *)suggested_addr, length, PROTECTION,
-			   MAP_HUGETLB | MAP_SHARED | MAP_POPULATE, fd, 0);
+	void *haddr = mmap((void *)suggested_addr, length, PROTECTION, FLAGS, fd, 0);
 	ksft_print_msg("Map haddr: Returned address is %p\n", haddr);
 	if (haddr == MAP_FAILED)
 		ksft_exit_fail_msg("mmap1: %s\n", strerror(errno));
 
 	/* mmap again to a dummy address to hopefully trigger pmd sharing. */
 	suggested_addr = 0x7daa40000000;
-	void *daddr = mmap((void *)suggested_addr, length, PROTECTION,
-			   MAP_HUGETLB | MAP_SHARED | MAP_POPULATE, fd, 0);
+	void *daddr = mmap((void *)suggested_addr, length, PROTECTION, FLAGS, fd, 0);
 	ksft_print_msg("Map daddr: Returned address is %p\n", daddr);
 	if (daddr == MAP_FAILED)
 		ksft_exit_fail_msg("mmap3: %s\n", strerror(errno));
 
 	suggested_addr = 0x7faa40000000;
-	void *vaddr =
-		mmap((void *)suggested_addr, length, PROTECTION, FLAGS, -1, 0);
+	void *vaddr = mmap((void *)suggested_addr, length, PROTECTION, FLAGS, fd, 0);
 	ksft_print_msg("Map vaddr: Returned address is %p\n", vaddr);
 	if (vaddr == MAP_FAILED)
 		ksft_exit_fail_msg("mmap2: %s\n", strerror(errno));
-- 
2.52.0