fixup! arm64: Implement Apple IMPDEF TSO memory model control

Author: hoshinolina

arch/arm64/kernel/cpufeature_impdef.c

@@ -3,14 +3,19 @@
  * Contains implementation-defined CPU feature definitions.
  */
 
+#define pr_fmt(fmt) "CPU features: " fmt
+
 #include <asm/cpufeature.h>
 #include <asm/apple_cpufeature.h>
+#include <linux/irqflags.h>
+#include <linux/preempt.h>
+#include <linux/printk.h>
 
 #ifdef CONFIG_ARM64_MEMORY_MODEL_CONTROL
 static bool has_apple_feature(const struct arm64_cpu_capabilities *entry, int scope)
 {
 	u64 val;
-	WARN_ON(scope != SCOPE_SYSTEM);
+	WARN_ON(scope == SCOPE_LOCAL_CPU && preemptible());
 
 	if (read_cpuid_implementor() != ARM_CPU_IMP_APPLE)
 		return false;
@@ -19,6 +24,30 @@ static bool has_apple_feature(const struct arm64_cpu_capabilities *entry, int sc
 	return cpufeature_matches(val, entry);
 }
 
+static bool has_apple_tso(const struct arm64_cpu_capabilities *entry, int scope)
+{
+	u64 val;
+
+	if (!has_apple_feature(entry, scope))
+		return false;
+
+	/*
+	 * KVM and old versions of the macOS hypervisor will advertise TSO in
+	 * AIDR_EL1, but then ignore writes to ACTLR_EL1. Test that the bit is
+	 * actually writable before enabling TSO.
+	 */
+
+	val = read_sysreg(actlr_el1);
+	write_sysreg(val ^ ACTLR_APPLE_TSO, actlr_el1);
+	if (!((val ^ read_sysreg(actlr_el1)) & ACTLR_APPLE_TSO)) {
+		pr_info_once("CPU advertises Apple TSO but it is broken, ignoring\n");
+		return false;
+	}
+
+	write_sysreg(val, actlr_el1);
+	return true;
+}
+
 static bool has_tso_fixed(const struct arm64_cpu_capabilities *entry, int scope)
 {
 	/* List of CPUs that always use the TSO memory model */
@@ -38,8 +67,8 @@ static const struct arm64_cpu_capabilities arm64_impdef_features[] = {
 	{
 		.desc = "TSO memory model (Apple)",
 		.capability = ARM64_HAS_TSO_APPLE,
-		.type = ARM64_CPUCAP_SYSTEM_FEATURE,
-		.matches = has_apple_feature,
+		.type = SCOPE_LOCAL_CPU | ARM64_CPUCAP_PERMITTED_FOR_LATE_CPU,
+		.matches = has_apple_tso,
 		.field_pos = AIDR_APPLE_TSO_SHIFT,
 		.field_width = 1,
 		.sign = FTR_UNSIGNED,