[PATCH 3/5] arm64: mte: CPU feature detection for Asymm MTE

[Vincenzo Frascino]

Add the cpufeature entries to detect the presence of Asymmetric MTE.

Note: The tag checking mode is initialized via cpu_enable_mte() ->
kasan_init_hw_tags() hence to enable it we require asymmetric mode
to be at least on the boot CPU. If the boot CPU does not have it, it is
fine for late CPUs to have it as long as the feature is not enabled
(ARM64_CPUCAP_BOOT_CPU_FEATURE).

Cc: Will Deacon <will@xxxxxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Suzuki K Poulose <Suzuki.Poulose@xxxxxxx>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@xxxxxxx>
---
 arch/arm64/kernel/cpufeature.c | 10 ++++++++++
 arch/arm64/tools/cpucaps       |  1 +
 2 files changed, 11 insertions(+)

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index f8a3067d10c6..a18774071a45 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -2317,6 +2317,16 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
 		.sign = FTR_UNSIGNED,
 		.cpu_enable = cpu_enable_mte,
 	},
+	{
+		.desc = "Asymmetric Memory Tagging Extension",
+		.capability = ARM64_MTE_ASYMM,
+		.type = ARM64_CPUCAP_BOOT_CPU_FEATURE,
+		.matches = has_cpuid_feature,
+		.sys_reg = SYS_ID_AA64PFR1_EL1,
+		.field_pos = ID_AA64PFR1_MTE_SHIFT,
+		.min_field_value = ID_AA64PFR1_MTE_ASYMM,
+		.sign = FTR_UNSIGNED,
+	},
 #endif /* CONFIG_ARM64_MTE */
 	{
 		.desc = "RCpc load-acquire (LDAPR)",
diff --git a/arch/arm64/tools/cpucaps b/arch/arm64/tools/cpucaps
index 49305c2e6dfd..74a569bf52d6 100644
--- a/arch/arm64/tools/cpucaps
+++ b/arch/arm64/tools/cpucaps
@@ -39,6 +39,7 @@ HW_DBM
 KVM_PROTECTED_MODE
 MISMATCHED_CACHE_TYPE
 MTE
+MTE_ASYMM
 SPECTRE_V2
 SPECTRE_V3A
 SPECTRE_V4
-- 
2.33.0