selftests/lam: Skip test if LAM is disabled

Until LASS is merged into the kernel:

  https://lore.kernel.org/all/20241028160917.1380714-1-alexander.shishkin@linux.intel.com/

LAM is left disabled in the config file. Running the LAM selftest with
disabled LAM only results in unhelpful output.

Use one of LAM syscalls() to determine whether the kernel was compiled
with LAM support (CONFIG_ADDRESS_MASKING) or not. Skip running the tests
in the latter case.

Merge CPUID checking function with the one mentioned above to achieve a
single function that shows LAM's availability from both CPU and the
kernel.

Signed-off-by: Maciej Wieczor-Retman <maciej.wieczor-retman@intel.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Link: https://lore.kernel.org/r/251d0f45f6a768030115e8d04bc85458910cb0dc.1737990375.git.maciej.wieczor-retman@intel.com

diff --git a/tools/testing/selftests/x86/lam.c b/tools/testing/selftests/x86/lam.c
index 60170a31aa6967787266863229d373ef6c82c383..df91a41a5babc4920fd231af9edbabd2d8a8ad47 100644 (file)
--- a/tools/testing/selftests/x86/lam.c
+++ b/tools/testing/selftests/x86/lam.c
@@ -115,13 +115,28 @@ static void segv_handler(int sig)
        siglongjmp(segv_env, 1);
 }
 
-static inline int cpu_has_lam(void)
+static inline int lam_is_available(void)
 {
        unsigned int cpuinfo[4];
+       unsigned long bits = 0;
+       int ret;
 
        __cpuid_count(0x7, 1, cpuinfo[0], cpuinfo[1], cpuinfo[2], cpuinfo[3]);
 
-       return (cpuinfo[0] & (1 << 26));
+       /* Check if cpu supports LAM */
+       if (!(cpuinfo[0] & (1 << 26))) {
+               ksft_print_msg("LAM is not supported!\n");
+               return 0;
+       }
+
+       /* Return 0 if CONFIG_ADDRESS_MASKING is not set */
+       ret = syscall(SYS_arch_prctl, ARCH_GET_MAX_TAG_BITS, &bits);
+       if (ret) {
+               ksft_print_msg("LAM is disabled in the kernel!\n");
+               return 0;
+       }
+
+       return 1;
 }
 
 static inline int la57_enabled(void)
@@ -1185,10 +1200,8 @@ int main(int argc, char **argv)
 
        tests_cnt = 0;
 
-       if (!cpu_has_lam()) {
-               ksft_print_msg("Unsupported LAM feature!\n");
+       if (!lam_is_available())
                return KSFT_SKIP;
-       }
 
        while ((c = getopt(argc, argv, "ht:")) != -1) {
                switch (c) {