selftest/mm: register existing mapping with userfaultfd in hugetlb-mremap

Previously, register_region_with_uffd() created a new anonymous mapping
and overwrote the address supplied by the caller before registering the
range with userfaultfd.

As a result, userfaultfd was applied to an unrelated anonymous mapping
instead of the hugetlb region used by the test.

Remove the extra mmap() and register the caller-provided address range
directly using UFFDIO_REGISTER_MODE_MISSING, so that faults are generated
for the hugetlb mapping used by the test.

This ensures userfaultfd operates on the actual hugetlb test region and
validates the expected fault handling.

Before patch:
 running ./hugetlb-mremap
 -------------------------
 TAP version 13
 1..1
  Map haddr: Returned address is 0x7eaa40000000
  Map daddr: Returned address is 0x7daa40000000
  Map vaddr: Returned address is 0x7faa40000000
  Address returned by mmap() = 0x7fff9d000000
  Mremap: Returned address is 0x7faa40000000
  First hex is 0
  First hex is 3020100
 ok 1 Read same data
 Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0
 [PASS]
 ok 1 hugetlb-mremap

After patch:
 running ./hugetb-mremap
 -------------------------
 TAP version 13
 1..1
  Map haddr: Returned address is 0x7eaa40000000
  Map daddr: Returned address is 0x7daa40000000
  Map vaddr: Returned address is 0x7faa40000000
  Registered memory at address 0x7eaa40000000 with userfaultfd
  Mremap: Returned address is 0x7faa40000000
  First hex is 0
  First hex is 3020100
 ok 1 Read same data
 Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0
 [PASS]
 ok 1 hugetlb-mremap

Link: https://lore.kernel.org/13845da872ed174316173e8996dbb5f181994017.1779296493.git.sayalip@linux.ibm.com
Fixes: 12b613206474 ("mm, hugepages: add hugetlb vma mremap() test")
Signed-off-by: Sayali Patil <sayalip@linux.ibm.com>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Tested-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: "Ritesh Harjani (IBM)" <ritesh.list@gmail.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/tools/testing/selftests/mm/hugetlb-mremap.c b/tools/testing/selftests/mm/hugetlb-mremap.c
index d239905790dd896da2b1fcf8e948a402b78aa55b..00b4c2cc95a66d1e6a06704bd6b87baeadc204d9 100644 (file)
--- a/tools/testing/selftests/mm/hugetlb-mremap.c
+++ b/tools/testing/selftests/mm/hugetlb-mremap.c
@@ -86,25 +86,14 @@ static void register_region_with_uffd(char *addr, size_t len)
        if (ioctl(uffd, UFFDIO_API, &uffdio_api) == -1)
                ksft_exit_fail_msg("ioctl-UFFDIO_API: %s\n", strerror(errno));
 
-       /* Create a private anonymous mapping. The memory will be
-        * demand-zero paged--that is, not yet allocated. When we
-        * actually touch the memory, it will be allocated via
-        * the userfaultfd.
-        */
-
-       addr = mmap(NULL, len, PROT_READ | PROT_WRITE,
-                   MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
-       if (addr == MAP_FAILED)
-               ksft_exit_fail_msg("mmap: %s\n", strerror(errno));
-
-       ksft_print_msg("Address returned by mmap() = %p\n", addr);
-
-       /* Register the memory range of the mapping we just created for
-        * handling by the userfaultfd object. In mode, we request to track
-        * missing pages (i.e., pages that have not yet been faulted in).
+       /* Register the passed memory range for handling by the userfaultfd object.
+        * In mode, we request to track missing pages
+        * (i.e., pages that have not yet been faulted in).
         */
        if (uffd_register(uffd, addr, len, true, false, false))
                ksft_exit_fail_msg("ioctl-UFFDIO_REGISTER: %s\n", strerror(errno));
+
+       ksft_print_msg("Registered memory at address %p with userfaultfd\n", addr);
 }
 
 int main(int argc, char *argv[])