selftests: memfd_secret: don't build memfd_secret test on unsupported arches

[1] mentions that memfd_secret is only supported on arm64, riscv, x86 and
x86_64 for now.  It doesn't support other architectures.  I found the
build error on arm and decided to send the fix as it was creating noise on
KernelCI:

memfd_secret.c: In function 'memfd_secret':
memfd_secret.c:42:24: error: '__NR_memfd_secret' undeclared (first use in this function);
did you mean 'memfd_secret'?
   42 |         return syscall(__NR_memfd_secret, flags);
      |                        ^~~~~~~~~~~~~~~~~
      |                        memfd_secret

Hence I'm adding condition that memfd_secret should only be compiled on
supported architectures.

Also check in run_vmtests script if memfd_secret binary is present before
executing it.

Link: https://lkml.kernel.org/r/[email protected]
Link: https://lore.kernel.org/all/[email protected]/ [1]
Link: https://lkml.kernel.org/r/[email protected]
Fixes: 76fe17e ("secretmem: test: add basic selftest for memfd_secret(2)")
Signed-off-by: Muhammad Usama Anjum <[email protected]>
Reviewed-by: Shuah Khan <[email protected]>
Acked-by: Mike Rapoport (Microsoft) <[email protected]>
Cc: Albert Ou <[email protected]>
Cc: James Bottomley <[email protected]>
Cc: Mike Rapoport (Microsoft) <[email protected]>
Cc: Palmer Dabbelt <[email protected]>
Cc: Paul Walmsley <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: Muhammad Usama Anjum

tools/testing/selftests/mm/Makefile

@@ -53,7 +53,9 @@ TEST_GEN_FILES += madv_populate
 TEST_GEN_FILES += map_fixed_noreplace
 TEST_GEN_FILES += map_hugetlb
 TEST_GEN_FILES += map_populate
+ifneq (,$(filter $(ARCH),arm64 riscv riscv64 x86 x86_64))
 TEST_GEN_FILES += memfd_secret
+endif
 TEST_GEN_FILES += migration
 TEST_GEN_FILES += mkdirty
 TEST_GEN_FILES += mlock-random-test

tools/testing/selftests/mm/run_vmtests.sh

@@ -374,8 +374,11 @@ CATEGORY="hmm" run_test bash ./test_hmm.sh smoke
 # MADV_POPULATE_READ and MADV_POPULATE_WRITE tests
 CATEGORY="madv_populate" run_test ./madv_populate
 
+if [ -x ./memfd_secret ]
+then
 (echo 0 | sudo tee /proc/sys/kernel/yama/ptrace_scope 2>&1) | tap_prefix
 CATEGORY="memfd_secret" run_test ./memfd_secret
+fi
 
 # KSM KSM_MERGE_TIME_HUGE_PAGES test with size of 100
 CATEGORY="ksm" run_test ./ksm_tests -H -s 100