[PATCH 06/11] kselftest/arm64: mte: Fix MTE feature detection

[Andre Przywara]

To check whether the CPU and kernel support the MTE features we want
to test, we use an (emulated) CPU ID register read. However we only
check against a very particular feature version (0b0010), even though
the ARM ARM promises ID register features to be backwards compatible.

While this could be fixed by using ">=" instead of "==", we should
actually use the explicit HWCAP2_MTE hardware capability, exposed by the
kernel via the ELF auxiliary vectors.

That moves this responsibility to the kernel, and fixes running the
tests on machines with FEAT_MTE3 capability.

Reviewed-by: Andre Przywara <andre.przywara at arm.com>
---
 tools/testing/selftests/arm64/mte/mte_common_util.c | 13 ++-----------
 1 file changed, 2 insertions(+), 11 deletions(-)

diff --git a/tools/testing/selftests/arm64/mte/mte_common_util.c b/tools/testing/selftests/arm64/mte/mte_common_util.c
index 4e887dad762d..aa8a8a6b8b6d 100644
--- a/tools/testing/selftests/arm64/mte/mte_common_util.c
+++ b/tools/testing/selftests/arm64/mte/mte_common_util.c
@@ -291,22 +291,13 @@ int mte_switch_mode(int mte_option, unsigned long incl_mask)
 	return 0;
 }
 
-#define ID_AA64PFR1_MTE_SHIFT		8
-#define ID_AA64PFR1_MTE			2
-
 int mte_default_setup(void)
 {
-	unsigned long hwcaps = getauxval(AT_HWCAP);
+	unsigned long hwcaps2 = getauxval(AT_HWCAP2);
 	unsigned long en = 0;
 	int ret;
 
-	if (!(hwcaps & HWCAP_CPUID)) {
-		ksft_print_msg("FAIL: CPUID registers unavailable\n");
-		return KSFT_FAIL;
-	}
-	/* Read ID_AA64PFR1_EL1 register */
-	asm volatile("mrs %0, id_aa64pfr1_el1" : "=r"(hwcaps) : : "memory");
-	if (((hwcaps >> ID_AA64PFR1_MTE_SHIFT) & MT_TAG_MASK) != ID_AA64PFR1_MTE) {
+	if (!(hwcaps2 & HWCAP2_MTE)) {
 		ksft_print_msg("FAIL: MTE features unavailable\n");
 		return KSFT_SKIP;
 	}
-- 
2.17.5