3 files changed, 26 insertions, 4 deletions
diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index a4d0b77a68d9..e0e4478f5fb5 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -671,6 +671,7 @@ static inline bool supports_clearbhb(int scope)
 }
 
 const struct cpumask *system_32bit_el0_cpumask(void);
+const struct cpumask *fallback_32bit_el0_cpumask(void);
 DECLARE_STATIC_KEY_FALSE(arm64_mismatched_32bit_el0);
 
 static inline bool system_supports_32bit_el0(void)
diff --git a/arch/arm64/include/asm/mmu_context.h b/arch/arm64/include/asm/mmu_context.h
index 48b3d9553b67..0dbe3b29049b 100644
--- a/arch/arm64/include/asm/mmu_context.h
+++ b/arch/arm64/include/asm/mmu_context.h
@@ -271,18 +271,26 @@ switch_mm(struct mm_struct *prev, struct mm_struct *next,
 }
 
 static inline const struct cpumask *
-task_cpu_possible_mask(struct task_struct *p)
+__task_cpu_possible_mask(struct task_struct *p, const struct cpumask *mask)
 {
 	if (!static_branch_unlikely(&arm64_mismatched_32bit_el0))
-		return cpu_possible_mask;
+		return mask;
 
 	if (!is_compat_thread(task_thread_info(p)))
-		return cpu_possible_mask;
+		return mask;
 
 	return system_32bit_el0_cpumask();
 }
+
+static inline const struct cpumask *
+task_cpu_possible_mask(struct task_struct *p)
+{
+	return __task_cpu_possible_mask(p, cpu_possible_mask);
+}
 #define task_cpu_possible_mask	task_cpu_possible_mask
 
+const struct cpumask *task_cpu_fallback_mask(struct task_struct *p);
+
 void verify_cpu_asid_bits(void);
 void post_ttbr_update_workaround(void);
 
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index d41128e37701..4eb7c6698ae4 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -75,6 +75,7 @@
 #include <linux/cpu.h>
 #include <linux/kasan.h>
 #include <linux/percpu.h>
+#include <linux/sched/isolation.h>
 
 #include <asm/cpu.h>
 #include <asm/cpufeature.h>
@@ -1644,6 +1645,11 @@ const struct cpumask *system_32bit_el0_cpumask(void)
 	return cpu_possible_mask;
 }
 
+const struct cpumask *task_cpu_fallback_mask(struct task_struct *p)
+{
+	return __task_cpu_possible_mask(p, housekeeping_cpumask(HK_TYPE_TICK));
+}
+
 static int __init parse_32bit_el0_param(char *str)
 {
 	allow_mismatched_32bit_el0 = true;
@@ -3773,7 +3779,14 @@ static int enable_mismatched_32bit_el0(unsigned int cpu)
 	static int lucky_winner = -1;
 
 	struct cpuinfo_arm64 *info = &per_cpu(cpu_data, cpu);
-	bool cpu_32bit = id_aa64pfr0_32bit_el0(info->reg_id_aa64pfr0);
+	bool cpu_32bit = false;
+
+	if (id_aa64pfr0_32bit_el0(info->reg_id_aa64pfr0)) {
+		if (!housekeeping_cpu(cpu, HK_TYPE_TICK))
+			pr_info("Treating adaptive-ticks CPU %u as 64-bit only\n", cpu);
+		else
+			cpu_32bit = true;
+	}
 
 	if (cpu_32bit) {
 		cpumask_set_cpu(cpu, cpu_32bit_el0_mask);