linux-kernel - [PATCH v4 1/3] selftests/lam: Move cpu_has

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Message-ID: <4979b3de7021f34cbef22d44799e28c914f993ca.1732627541.git.maciej.wieczor-retman@intel.com>
Date: Tue, 26 Nov 2024 14:34:48 +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 v4 1/3] selftests/lam: Move cpu_has_la57() to use cpuinfo flag

In current form cpu_has_la57() reports platform's support for LA57
through reading the output of cpuid. A much more useful information is
whether 5-level paging is actually enabled on the running system.

Presence of the la57 flag in /proc/cpuinfo signifies that 5-level paging
was compiled into the kernel, is supported by the platform and wasn't
disabled by kernel command line argument.

Use system() with cat and grep to figure out if la57 is enabled on the
running system.

Signed-off-by: Maciej Wieczor-Retman <maciej.wieczor-retman@...el.com>
---
Changelog v4:
- Add this patch to the series.

 tools/testing/selftests/x86/lam.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/tools/testing/selftests/x86/lam.c b/tools/testing/selftests/x86/lam.c
index 0ea4f6813930..0ac805125ab2 100644
--- a/tools/testing/selftests/x86/lam.c
+++ b/tools/testing/selftests/x86/lam.c
@@ -124,14 +124,11 @@ static inline int cpu_has_lam(void)
 	return (cpuinfo[0] & (1 << 26));
 }
 
-/* Check 5-level page table feature in CPUID.(EAX=07H, ECX=00H):ECX.[bit 16] */
 static inline int cpu_has_la57(void)
 {
-	unsigned int cpuinfo[4];
-
-	__cpuid_count(0x7, 0, cpuinfo[0], cpuinfo[1], cpuinfo[2], cpuinfo[3]);
+	int ret = !!system("cat /proc/cpuinfo | grep -wq la57\n");
 
-	return (cpuinfo[2] & (1 << 16));
+	return !ret;
 }
 
 /*
-- 
2.47.1