linux-kernel - [PATCH v6 1/3] selftests/lam: Move cpu_has

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Message-ID: <8b1ca51b13e6d94b5a42b6930d81b692cbb0bcbb.1737990375.git.maciej.wieczor-retman@intel.com>
Date: Mon, 27 Jan 2025 16:31:55 +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 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.

Check whether 5-level paging is enabled by trying to map a page in the
high linear address space.

Signed-off-by: Maciej Wieczor-Retman <maciej.wieczor-retman@...el.com>
---
Changelog v6:
- Go back to using mmap() to check la57 status.

Changelog v5:
- Remove "cat" from system() call and use only "grep".

Changelog v4:
- Add this patch to the series.

 tools/testing/selftests/x86/lam.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/tools/testing/selftests/x86/lam.c b/tools/testing/selftests/x86/lam.c
index 0ea4f6813930..1ce6cf322c3c 100644
--- a/tools/testing/selftests/x86/lam.c
+++ b/tools/testing/selftests/x86/lam.c
@@ -124,14 +124,18 @@ 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)
+static inline int la57_enabled(void)
 {
-	unsigned int cpuinfo[4];
+	int ret;
+	void *p;
+
+	p = mmap((void *)HIGH_ADDR, PAGE_SIZE, PROT_READ | PROT_WRITE,
+		 MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED, -1, 0);
 
-	__cpuid_count(0x7, 0, cpuinfo[0], cpuinfo[1], cpuinfo[2], cpuinfo[3]);
+	ret = p == MAP_FAILED ? 0 : 1;
 
-	return (cpuinfo[2] & (1 << 16));
+	munmap(p, PAGE_SIZE);
+	return ret;
 }
 
 /*
@@ -322,7 +326,7 @@ static int handle_mmap(struct testcases *test)
 		   flags, -1, 0);
 	if (ptr == MAP_FAILED) {
 		if (test->addr == HIGH_ADDR)
-			if (!cpu_has_la57())
+			if (!la57_enabled())
 				return 3; /* unsupport LA57 */
 		return 1;
 	}
-- 
2.47.1