linux-kernel - [PATCH v6 2/3] selftests/lam: Skip test if LAM is disabled

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Message-ID: <251d0f45f6a768030115e8d04bc85458910cb0dc.1737990375.git.maciej.wieczor-retman@intel.com>
Date: Mon, 27 Jan 2025 16:31:56 +0100
From: Maciej Wieczor-Retman <maciej.wieczor-retman@...el.com>
To: shuah@...nel.org,
	hpa@...or.com,
	x86@...nel.org,
	dave.hansen@...ux.intel.com,
	bp@...en8.de,
	mingo@...hat.com,
	tglx@...utronix.de
Cc: linux-kernel@...r.kernel.org,
	linux-kselftest@...r.kernel.org,
	kirill@...temov.name,
	maciej.wieczor-retman@...el.com
Subject: [PATCH v6 2/3] selftests/lam: Skip test if LAM is disabled

Until LASS is merged into the kernel [1], 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.

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

Signed-off-by: Maciej Wieczor-Retman <maciej.wieczor-retman@...el.com>
---
Changelog v6:
- Merge cpuid and kernel_has_lam() functions into one
  lam_is_available().

Changelog v4:
- Add this patch to the series.

 tools/testing/selftests/x86/lam.c | 23 ++++++++++++++++++-----
 1 file changed, 18 insertions(+), 5 deletions(-)

diff --git a/tools/testing/selftests/x86/lam.c b/tools/testing/selftests/x86/lam.c
index 1ce6cf322c3c..140011bc39c0 100644
--- 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) {
-- 
2.47.1