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context.c

/*
 *  linux/arch/arm/mm/context.c
 *
 *  Copyright (C) 2002-2003 Deep Blue Solutions Ltd, all rights reserved.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */
#include <linux/init.h>
#include <linux/sched.h>
#include <linux/mm.h>
#include <linux/smp.h>
#include <linux/percpu.h>

#include <asm/mmu_context.h>
#include <asm/tlbflush.h>

static DEFINE_SPINLOCK(cpu_asid_lock);
unsigned int cpu_last_asid = ASID_FIRST_VERSION;
#ifdef CONFIG_SMP
DEFINE_PER_CPU(struct mm_struct *, current_mm);
#endif

/*
 * We fork()ed a process, and we need a new context for the child
 * to run in.  We reserve version 0 for initial tasks so we will
 * always allocate an ASID. The ASID 0 is reserved for the TTBR
 * register changing sequence.
 */
void __init_new_context(struct task_struct *tsk, struct mm_struct *mm)
{
      mm->context.id = 0;
      spin_lock_init(&mm->context.id_lock);
}

static void flush_context(void)
{
      /* set the reserved ASID before flushing the TLB */
      asm("mcr    p15, 0, %0, c13, c0, 1\n" : : "r" (0));
      isb();
      local_flush_tlb_all();
      if (icache_is_vivt_asid_tagged()) {
            __flush_icache_all();
            dsb();
      }
}

#ifdef CONFIG_SMP

static void set_mm_context(struct mm_struct *mm, unsigned int asid)
{
      unsigned long flags;

      /*
       * Locking needed for multi-threaded applications where the
       * same mm->context.id could be set from different CPUs during
       * the broadcast. This function is also called via IPI so the
       * mm->context.id_lock has to be IRQ-safe.
       */
      spin_lock_irqsave(&mm->context.id_lock, flags);
      if (likely((mm->context.id ^ cpu_last_asid) >> ASID_BITS)) {
            /*
             * Old version of ASID found. Set the new one and
             * reset mm_cpumask(mm).
             */
            mm->context.id = asid;
            cpumask_clear(mm_cpumask(mm));
      }
      spin_unlock_irqrestore(&mm->context.id_lock, flags);

      /*
       * Set the mm_cpumask(mm) bit for the current CPU.
       */
      cpumask_set_cpu(smp_processor_id(), mm_cpumask(mm));
}

/*
 * Reset the ASID on the current CPU. This function call is broadcast
 * from the CPU handling the ASID rollover and holding cpu_asid_lock.
 */
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;

      smp_rmb();
      asid = cpu_last_asid + cpu + 1;

      flush_context();
      set_mm_context(mm, asid);

      /* set the new ASID */
      asm("mcr    p15, 0, %0, c13, c0, 1\n" : : "r" (mm->context.id));
      isb();
}

#else

static inline void set_mm_context(struct mm_struct *mm, unsigned int asid)
{
      mm->context.id = asid;
      cpumask_copy(mm_cpumask(mm), cpumask_of(smp_processor_id()));
}

#endif

void __new_context(struct mm_struct *mm)
{
      unsigned int asid;

      spin_lock(&cpu_asid_lock);
#ifdef CONFIG_SMP
      /*
       * Check the ASID again, in case the change was broadcast from
       * another CPU before we acquired the lock.
       */
      if (unlikely(((mm->context.id ^ cpu_last_asid) >> ASID_BITS) == 0)) {
            cpumask_set_cpu(smp_processor_id(), mm_cpumask(mm));
            spin_unlock(&cpu_asid_lock);
            return;
      }
#endif
      /*
       * At this point, it is guaranteed that the current mm (with
       * an old ASID) isn't active on any other CPU since the ASIDs
       * are changed simultaneously via IPI.
       */
      asid = ++cpu_last_asid;
      if (asid == 0)
            asid = cpu_last_asid = ASID_FIRST_VERSION;

      /*
       * If we've used up all our ASIDs, we need
       * to start a new version and flush the TLB.
       */
      if (unlikely((asid & ~ASID_MASK) == 0)) {
            asid = cpu_last_asid + smp_processor_id() + 1;
            flush_context();
#ifdef CONFIG_SMP
            smp_wmb();
            smp_call_function(reset_context, NULL, 1);
#endif
            cpu_last_asid += NR_CPUS;
      }

      set_mm_context(mm, asid);
      spin_unlock(&cpu_asid_lock);
}

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