arch/arm/mm/context.c

   1 /*
   2  *  linux/arch/arm/mm/context.c
   3  *
   4  *  Copyright (C) 2002-2003 Deep Blue Solutions Ltd, all rights reserved.
   5  *  Copyright (C) 2012 ARM Limited
   6  *
   7  *  Author: Will Deacon <will.deacon@arm.com>
   8  *
   9  * This program is free software; you can redistribute it and/or modify
  10  * it under the terms of the GNU General Public License version 2 as
  11  * published by the Free Software Foundation.
  12  */
  13 #include <linux/init.h>
  14 #include <linux/sched.h>
  15 #include <linux/mm.h>
  16 #include <linux/smp.h>
  17 #include <linux/percpu.h>
  18
  19 #include <asm/mmu_context.h>
  20 #include <asm/smp_plat.h>
  21 #include <asm/thread_notify.h>
  22 #include <asm/tlbflush.h>
  23 #include <asm/proc-fns.h>
  24
  25 /*
  26  * On ARMv6, we have the following structure in the Context ID:
  27  *
  28  * 31                         7          0
  29  * +-------------------------+-----------+
  30  * |      process ID         |   ASID    |
  31  * +-------------------------+-----------+
  32  * |              context ID             |
  33  * +-------------------------------------+
  34  *
  35  * The ASID is used to tag entries in the CPU caches and TLBs.
  36  * The context ID is used by debuggers and trace logic, and
  37  * should be unique within all running processes.
  38  *
  39  * In big endian operation, the two 32 bit words are swapped if accesed by
  40  * non 64-bit operations.
  41  */
  42 #define ASID_FIRST_VERSION      (1ULL << ASID_BITS)
  43 #define NUM_USER_ASIDS          ASID_FIRST_VERSION
  44
  45 static DEFINE_RAW_SPINLOCK(cpu_asid_lock);
  46 static atomic64_t asid_generation = ATOMIC64_INIT(ASID_FIRST_VERSION);
  47 static DECLARE_BITMAP(asid_map, NUM_USER_ASIDS);
  48
  49 static DEFINE_PER_CPU(atomic64_t, active_asids);
  50 static DEFINE_PER_CPU(u64, reserved_asids);
  51 static cpumask_t tlb_flush_pending;
  52
  53 #ifdef CONFIG_ARM_ERRATA_798181
  54 void a15_erratum_get_cpumask(int this_cpu, struct mm_struct *mm,
  55                              cpumask_t *mask)
  56 {
  57         int cpu;
  58         unsigned long flags;
  59         u64 context_id, asid;
  60
  61         raw_spin_lock_irqsave(&cpu_asid_lock, flags);
  62         context_id = mm->context.id.counter;
  63         for_each_online_cpu(cpu) {
  64                 if (cpu == this_cpu)
  65                         continue;
  66                 /*
  67                  * We only need to send an IPI if the other CPUs are
  68                  * running the same ASID as the one being invalidated.
  69                  */
  70                 asid = per_cpu(active_asids, cpu).counter;
  71                 if (asid == 0)
  72                         asid = per_cpu(reserved_asids, cpu);
  73                 if (context_id == asid)
  74                         cpumask_set_cpu(cpu, mask);
  75         }
  76         raw_spin_unlock_irqrestore(&cpu_asid_lock, flags);
  77 }
  78 #endif
  79
  80 #ifdef CONFIG_ARM_LPAE
  81 static void cpu_set_reserved_ttbr0(void)
  82 {
  83         /*
  84          * Set TTBR0 to swapper_pg_dir which contains only global entries. The
  85          * ASID is set to 0.
  86          */
  87         cpu_set_ttbr(0, __pa(swapper_pg_dir));
  88         isb();
  89 }
  90 #else
  91 static void cpu_set_reserved_ttbr0(void)
  92 {
  93         u32 ttb;
  94         /* Copy TTBR1 into TTBR0 */
  95         asm volatile(
  96         "       mrc     p15, 0, %0, c2, c0, 1           @ read TTBR1\n"
  97         "       mcr     p15, 0, %0, c2, c0, 0           @ set TTBR0\n"
  98         : "=r" (ttb));
  99         isb();
 100 }
 101 #endif
 102
 103 #ifdef CONFIG_PID_IN_CONTEXTIDR
 104 static int contextidr_notifier(struct notifier_block *unused, unsigned long cmd,
 105                                void *t)
 106 {
 107         u32 contextidr;
 108         pid_t pid;
 109         struct thread_info *thread = t;
 110
 111         if (cmd != THREAD_NOTIFY_SWITCH)
 112                 return NOTIFY_DONE;
 113
 114         pid = task_pid_nr(thread->task) << ASID_BITS;
 115         asm volatile(
 116         "       mrc     p15, 0, %0, c13, c0, 1\n"
 117         "       and     %0, %0, %2\n"
 118         "       orr     %0, %0, %1\n"
 119         "       mcr     p15, 0, %0, c13, c0, 1\n"
 120         : "=r" (contextidr), "+r" (pid)
 121         : "I" (~ASID_MASK));
 122         isb();
 123
 124         return NOTIFY_OK;
 125 }
 126
 127 static struct notifier_block contextidr_notifier_block = {
 128         .notifier_call = contextidr_notifier,
 129 };
 130
 131 static int __init contextidr_notifier_init(void)
 132 {
 133         return thread_register_notifier(&contextidr_notifier_block);
 134 }
 135 arch_initcall(contextidr_notifier_init);
 136 #endif
 137
 138 static void flush_context(unsigned int cpu)
 139 {
 140         int i;
 141         u64 asid;
 142
 143         /* Update the list of reserved ASIDs and the ASID bitmap. */
 144         bitmap_clear(asid_map, 0, NUM_USER_ASIDS);
 145         for_each_possible_cpu(i) {
 146                 if (i == cpu) {
 147                         asid = 0;
 148                 } else {
 149                         asid = atomic64_xchg(&per_cpu(active_asids, i), 0);
 150                         /*
 151                          * If this CPU has already been through a
 152                          * rollover, but hasn't run another task in
 153                          * the meantime, we must preserve its reserved
 154                          * ASID, as this is the only trace we have of
 155                          * the process it is still running.
 156                          */
 157                         if (asid == 0)
 158                                 asid = per_cpu(reserved_asids, i);
 159                         __set_bit(asid & ~ASID_MASK, asid_map);
 160                 }
 161                 per_cpu(reserved_asids, i) = asid;
 162         }
 163
 164         /* Queue a TLB invalidate and flush the I-cache if necessary. */
 165         cpumask_setall(&tlb_flush_pending);
 166
 167         if (icache_is_vivt_asid_tagged())
 168                 __flush_icache_all();
 169 }
 170
 171 static int is_reserved_asid(u64 asid)
 172 {
 173         int cpu;
 174         for_each_possible_cpu(cpu)
 175                 if (per_cpu(reserved_asids, cpu) == asid)
 176                         return 1;
 177         return 0;
 178 }
 179
 180 static u64 new_context(struct mm_struct *mm, unsigned int cpu)
 181 {
 182         u64 asid = atomic64_read(&mm->context.id);
 183         u64 generation = atomic64_read(&asid_generation);
 184
 185         if (asid != 0 && is_reserved_asid(asid)) {
 186                 /*
 187                  * Our current ASID was active during a rollover, we can
 188                  * continue to use it and this was just a false alarm.
 189                  */
 190                 asid = generation | (asid & ~ASID_MASK);
 191         } else {
 192                 /*
 193                  * Allocate a free ASID. If we can't find one, take a
 194                  * note of the currently active ASIDs and mark the TLBs
 195                  * as requiring flushes. We always count from ASID #1,
 196                  * as we reserve ASID #0 to switch via TTBR0 and indicate
 197                  * rollover events.
 198                  */
 199                 asid = find_next_zero_bit(asid_map, NUM_USER_ASIDS, 1);
 200                 if (asid == NUM_USER_ASIDS) {
 201                         generation = atomic64_add_return(ASID_FIRST_VERSION,
 202                                                          &asid_generation);
 203                         flush_context(cpu);
 204                         asid = find_next_zero_bit(asid_map, NUM_USER_ASIDS, 1);
 205                 }
 206                 __set_bit(asid, asid_map);
 207                 asid |= generation;
 208                 cpumask_clear(mm_cpumask(mm));
 209         }
 210
 211         return asid;
 212 }
 213
 214 void check_and_switch_context(struct mm_struct *mm, struct task_struct *tsk)
 215 {
 216         unsigned long flags;
 217         unsigned int cpu = smp_processor_id();
 218         u64 asid;
 219
 220         if (unlikely(mm->context.vmalloc_seq != init_mm.context.vmalloc_seq))
 221                 __check_vmalloc_seq(mm);
 222
 223         /*
 224          * Required during context switch to avoid speculative page table
 225          * walking with the wrong TTBR.
 226          */
 227         cpu_set_reserved_ttbr0();
 228
 229         asid = atomic64_read(&mm->context.id);
 230         if (!((asid ^ atomic64_read(&asid_generation)) >> ASID_BITS)
 231             && atomic64_xchg(&per_cpu(active_asids, cpu), asid))
 232                 goto switch_mm_fastpath;
 233
 234         raw_spin_lock_irqsave(&cpu_asid_lock, flags);
 235         /* Check that our ASID belongs to the current generation. */
 236         asid = atomic64_read(&mm->context.id);
 237         if ((asid ^ atomic64_read(&asid_generation)) >> ASID_BITS) {
 238                 asid = new_context(mm, cpu);
 239                 atomic64_set(&mm->context.id, asid);
 240         }
 241
 242         if (cpumask_test_and_clear_cpu(cpu, &tlb_flush_pending)) {
 243                 local_flush_bp_all();
 244                 local_flush_tlb_all();
 245         }
 246
 247         atomic64_set(&per_cpu(active_asids, cpu), asid);
 248         cpumask_set_cpu(cpu, mm_cpumask(mm));
 249         raw_spin_unlock_irqrestore(&cpu_asid_lock, flags);
 250
 251 switch_mm_fastpath:
 252         cpu_switch_mm(mm->pgd, mm);
 253 }