[PATCH 1/1] arm64/cpufeature: Add option to disable mte support

[yee.lee]

From: Yee Lee <yee.lee@xxxxxxxxxxxx>

Add a static key to exapnd the logic of system_supports_mte().
This function controls mte enablement in both EL1 and EL0.

The static key, "arm64_mte_support" is default true and can
be disabled via the early_param.

Signed-off-by: Yee Lee <yee.lee@xxxxxxxxxxxx>
---
 arch/arm64/include/asm/cpufeature.h |  4 +++-
 arch/arm64/kernel/cpufeature.c      | 13 +++++++++++++
 arch/arm64/kernel/image-vars.h      |  3 +++
 3 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index 9bb9d11750d7..0e5c82f2e012 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -420,6 +420,7 @@ static __always_inline bool is_hyp_code(void)
 extern DECLARE_BITMAP(cpu_hwcaps, ARM64_NCAPS);
 extern struct static_key_false cpu_hwcap_keys[ARM64_NCAPS];
 extern struct static_key_false arm64_const_caps_ready;
+extern struct static_key_true arm64_mte_support;
 
 /* ARM64 CAPS + alternative_cb */
 #define ARM64_NPATCHABLE (ARM64_NCAPS + 1)
@@ -756,7 +757,8 @@ static __always_inline bool system_uses_irq_prio_masking(void)
 static inline bool system_supports_mte(void)
 {
 	return IS_ENABLED(CONFIG_ARM64_MTE) &&
-		cpus_have_const_cap(ARM64_MTE);
+		cpus_have_const_cap(ARM64_MTE) &&
+		static_branch_likely(&arm64_mte_support);
 }
 
 static inline bool system_has_prio_mask_debugging(void)
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 0ead8bfedf20..b1602ad3d7c0 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -1840,9 +1840,22 @@ static void bti_enable(const struct arm64_cpu_capabilities *__unused)
 }
 #endif /* CONFIG_ARM64_BTI */
 
+DEFINE_STATIC_KEY_TRUE(arm64_mte_support);
+EXPORT_SYMBOL(arm64_mte_support);
 #ifdef CONFIG_ARM64_MTE
+static int __init disable_arm64_mte_support(char *str)
+{
+	static_branch_disable(&arm64_mte_support);
+	return 0;
+}
+early_param("arm64_mte_not_support", disable_arm64_mte_support);
+
 static void cpu_enable_mte(struct arm64_cpu_capabilities const *cap)
 {
+	if(!system_supports_mte()){
+		pr_info("MTE is disabled since system does not support.\n");
+		return ;
+	}
 	/*
 	 * Clear the tags in the zero page. This needs to be done via the
 	 * linear map which has the Tagged attribute.
diff --git a/arch/arm64/kernel/image-vars.h b/arch/arm64/kernel/image-vars.h
index c96a9a0043bf..04cf30ec84e7 100644
--- a/arch/arm64/kernel/image-vars.h
+++ b/arch/arm64/kernel/image-vars.h
@@ -83,6 +83,9 @@ KVM_NVHE_ALIAS(__icache_flags);
 KVM_NVHE_ALIAS(arm64_const_caps_ready);
 KVM_NVHE_ALIAS(cpu_hwcap_keys);
 
+/* Static key which indicates if system supports mte */
+KVM_NVHE_ALIAS(arm64_mte_support);
+
 /* Static keys which are set if a vGIC trap should be handled in hyp. */
 KVM_NVHE_ALIAS(vgic_v2_cpuif_trap);
 KVM_NVHE_ALIAS(vgic_v3_cpuif_trap);
-- 
2.18.0