[PATCH v2 2/2] arm64: cpufeature: Pretend that Apple A10 family does not support 32-bit EL0

[Nick Chan]

The Apple A10 family consists of physical performance and efficiency
cores, and only one of them can be active at a given time depending on
the current p-state. However, only the performance cores can execute
32-bit EL0. This results in logical cores that can only execute 32-bit
EL0 in high p-states.

Trying to support 32-bit EL0 on a CPU that can only execute it in certain
states is a bad idea. The A10 family only supports 16KB page size anyway
so many AArch32 executables won't run anyways. Pretend that it does not
support 32-bit EL0 at all.

Signed-off-by: Nick Chan <towinchenmi@xxxxxxxxx>
---
 arch/arm64/kernel/cpufeature.c | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 718728a85430..386698f42172 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -3529,6 +3529,31 @@ void __init setup_boot_cpu_features(void)
 	setup_boot_cpu_capabilities();
 }
 
+static void __init bad_aarch32_el0_fixup(void)
+{
+	static const struct midr_range bad_aarch32_el0[] = {
+		MIDR_ALL_VERSIONS(MIDR_APPLE_A10_T2_HURRICANE_ZEPHYR),
+		MIDR_ALL_VERSIONS(MIDR_APPLE_A10X_HURRICANE_ZEPHYR),
+		{}
+	};
+
+	/*
+	 * The Apple A10 family can only execute 32-bit EL0 when in high
+	 * p-states. Pretend it does not support 32-bit EL0.
+	 */
+	if (is_midr_in_range_list(read_cpuid_id(), bad_aarch32_el0)) {
+		struct arm64_ftr_reg *regp;
+
+		regp = get_arm64_ftr_reg(SYS_ID_AA64PFR0_EL1);
+		if (!regp)
+			return;
+		u64 val = (regp->sys_val & ~ID_AA64PFR0_EL1_EL0_MASK)
+		  | ID_AA64PFR0_EL1_EL0_IMP;
+
+		update_cpu_ftr_reg(regp, val);
+	}
+}
+
 static void __init setup_system_capabilities(void)
 {
 	/*
@@ -3562,6 +3587,8 @@ static void __init setup_system_capabilities(void)
 
 void __init setup_system_features(void)
 {
+	bad_aarch32_el0_fixup();
+
 	setup_system_capabilities();
 
 	kpti_install_ng_mappings();
-- 
2.46.0