[PATCH v2] selftests/vm: Only run 128TBswitch with 5-level paging

[Adam Sindelar <adam@xxxxxxxxxxxx>]

The test va_128TBswitch.c expects to be able to pass mmap an address hint
and length that cross the address 1<<47. This is not possible without
5-level page tables, so the test fails.

The test is already only run on 64-bit powerpc and x86 archs, but this
patch adds an additional check that skips the test if PG_TABLE_LEVELS < 5.
There is precedent for checking /proc/config.gz in selftests, e.g. in
selftests/firmware.

Running `sudo make -C tools/testing/selftests TARGETS=vm run_tests`
produces the desired output:

```
---------------------------
running ./va_128TBswitch.sh
---------------------------
./va_128TBswitch.sh: PG_TABLE_LEVELS=4, must be >= 5 to run this test
[SKIP]
-------------------------------
```

v2:
  - Function variables declared local
  - Fixed variable name typo in Makefile
  - Comment to explain gzip -dcfq

Signed-off-by: Adam Sindelar <adam@xxxxxxxxxxxx>
---
 tools/testing/selftests/vm/Makefile          |  1 +
 tools/testing/selftests/vm/run_vmtests.sh    |  2 +-
 tools/testing/selftests/vm/va_128TBswitch.sh | 39 ++++++++++++++++++++
 3 files changed, 41 insertions(+), 1 deletion(-)
 create mode 100755 tools/testing/selftests/vm/va_128TBswitch.sh

diff --git a/tools/testing/selftests/vm/Makefile b/tools/testing/selftests/vm/Makefile
index c45e535ff4b8..7860d0969888 100644
--- a/tools/testing/selftests/vm/Makefile
+++ b/tools/testing/selftests/vm/Makefile
@@ -91,6 +91,7 @@ endif
 TEST_PROGS := run_vmtests.sh
 
 TEST_FILES := test_vmalloc.sh
+TEST_FILES += va_128TBswitch.sh
 
 KSFT_KHDR_INSTALL := 1
 include ../lib.mk
diff --git a/tools/testing/selftests/vm/run_vmtests.sh b/tools/testing/selftests/vm/run_vmtests.sh
index a2302b5faaf2..edda7350ccca 100755
--- a/tools/testing/selftests/vm/run_vmtests.sh
+++ b/tools/testing/selftests/vm/run_vmtests.sh
@@ -149,7 +149,7 @@ if [ $VADDR64 -ne 0 ]; then
 	run_test ./virtual_address_range
 
 	# virtual address 128TB switch test
-	run_test ./va_128TBswitch
+	run_test ./va_128TBswitch.sh
 fi # VADDR64
 
 # vmalloc stability smoke test
diff --git a/tools/testing/selftests/vm/va_128TBswitch.sh b/tools/testing/selftests/vm/va_128TBswitch.sh
new file mode 100755
index 000000000000..767a6465b5d2
--- /dev/null
+++ b/tools/testing/selftests/vm/va_128TBswitch.sh
@@ -0,0 +1,39 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+#
+# Copyright (C) 2022 Adam Sindelar (Meta) <adam@xxxxxxxxxxxx>
+#
+# This is a test for mmap behavior with 5-level paging. This script wraps the
+# real test to check that the kernel is configured to support at least 5
+# pagetable levels.
+
+# 1 means the test failed
+exitcode=1
+
+# Kselftest framework requirement - SKIP code is 4.
+ksft_skip=4
+
+die()
+{
+    echo "$1"
+    exit $exitcode
+}
+
+check_test_requirements()
+{
+    local config="/proc/config.gz"
+    [[ -f "${config}" ]] || config="/boot/config-$(uname -r)"
+    [[ -f "${config}" ]] || die "Cannot find kernel config in /proc or /boot"
+
+    # gzip -dcfq automatically handles both compressed and plaintext input.
+    # See man 1 gzip under '-f'.
+    local pg_table_levels=$(gzip -dcfq "${config}" | grep PGTABLE_LEVELS | cut -d'=' -f 2)
+
+    if [[ "${pg_table_levels}" -lt 5 ]]; then
+        echo "$0: PG_TABLE_LEVELS=${pg_table_levels}, must be >= 5 to run this test"
+        exit $ksft_skip
+    fi
+}
+
+check_test_requirements
+./va_128TBswitch
-- 
2.35.1