ARM: Remove current_mm per-cpu variable

The current_mm variable was used to store the new mm between the
switch_mm() and switch_to() calls where an IPI to reset the context
could have set the wrong mm. Since the interrupts are disabled during
context switch, there is no need for this variable, current->active_mm
already points to the current mm when interrupts are re-enabled.

Reviewed-by: Will Deacon <will.deacon@arm.com>
Tested-by: Will Deacon <will.deacon@arm.com>
Reviewed-by: Frank Rowand <frank.rowand@am.sony.com>
Tested-by: Marc Zyngier <Marc.Zyngier@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm/include/asm/mmu_context.h

@@ -43,9 +43,6 @@ void __check_kvm_seq(struct mm_struct *mm);
 #define ASID_FIRST_VERSION	(1 << ASID_BITS)
 
 extern unsigned int cpu_last_asid;
-#ifdef CONFIG_SMP
-DECLARE_PER_CPU(struct mm_struct *, current_mm);
-#endif
 
 void __init_new_context(struct task_struct *tsk, struct mm_struct *mm);
 void __new_context(struct mm_struct *mm);
@@ -160,10 +157,6 @@ switch_mm(struct mm_struct *prev, struct mm_struct *next,
 		__flush_icache_all();
 #endif
 	if (!cpumask_test_and_set_cpu(cpu, mm_cpumask(next)) || prev != next) {
-#ifdef CONFIG_SMP
-		struct mm_struct **crt_mm = &per_cpu(current_mm, cpu);
-		*crt_mm = next;
-#endif
 		check_and_switch_context(next, tsk);
 		if (cache_is_vivt())
 			cpumask_clear_cpu(cpu, mm_cpumask(prev));

arch/arm/mm/context.c

@@ -18,9 +18,6 @@
 
 static DEFINE_RAW_SPINLOCK(cpu_asid_lock);
 unsigned int cpu_last_asid = ASID_FIRST_VERSION;
-#ifdef CONFIG_SMP
-DEFINE_PER_CPU(struct mm_struct *, current_mm);
-#endif
 
 #ifdef CONFIG_ARM_LPAE
 void cpu_set_reserved_ttbr0(void)
@@ -108,14 +105,7 @@ static void reset_context(void *info)
 {
 	unsigned int asid;
 	unsigned int cpu = smp_processor_id();
-	struct mm_struct *mm = per_cpu(current_mm, cpu);
-
-	/*
-	 * Check if a current_mm was set on this CPU as it might still
-	 * be in the early booting stages and using the reserved ASID.
-	 */
-	if (!mm)
-		return;
+	struct mm_struct *mm = current->active_mm;
 
 	smp_rmb();
 	asid = cpu_last_asid + cpu + 1;