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 accessed
  40  * by 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 /*
  82  * With LPAE, the ASID and page tables are updated atomicly, so there is
  83  * no need for a reserved set of tables (the active ASID tracking prevents
  84  * any issues across a rollover).
  85  */
  86 #define cpu_set_reserved_ttbr0()
  87 #else
  88 static void cpu_set_reserved_ttbr0(void)
  89 {
  90         u32 ttb;
  91         /*
  92          * Copy TTBR1 into TTBR0.
  93          * This points at swapper_pg_dir, which contains only global
  94          * entries so any speculative walks are perfectly safe.
  95          */
  96         asm volatile(
  97         "       mrc     p15, 0, %0, c2, c0, 1           @ read TTBR1\n"
  98         "       mcr     p15, 0, %0, c2, c0, 0           @ set TTBR0\n"
  99         : "=r" (ttb));
 100         isb();
 101 }
 102 #endif
 103
 104 #ifdef CONFIG_PID_IN_CONTEXTIDR
 105 static int contextidr_notifier(struct notifier_block *unused, unsigned long cmd,
 106                                void *t)
 107 {
 108         u32 contextidr;
 109         pid_t pid;
 110         struct thread_info *thread = t;
 111
 112         if (cmd != THREAD_NOTIFY_SWITCH)
 113                 return NOTIFY_DONE;
 114
 115         pid = task_pid_nr(thread->task) << ASID_BITS;
 116         asm volatile(
 117         "       mrc     p15, 0, %0, c13, c0, 1\n"
 118         "       and     %0, %0, %2\n"
 119         "       orr     %0, %0, %1\n"
 120         "       mcr     p15, 0, %0, c13, c0, 1\n"
 121         : "=r" (contextidr), "+r" (pid)
 122         : "I" (~ASID_MASK));
 123         isb();
 124
 125         return NOTIFY_OK;
 126 }
 127
 128 static struct notifier_block contextidr_notifier_block = {
 129         .notifier_call = contextidr_notifier,
 130 };
 131
 132 static int __init contextidr_notifier_init(void)
 133 {
 134         return thread_register_notifier(&contextidr_notifier_block);
 135 }
 136 arch_initcall(contextidr_notifier_init);
 137 #endif
 138
 139 static void flush_context(unsigned int cpu)
 140 {
 141         int i;
 142         u64 asid;
 143
 144         /* Update the list of reserved ASIDs and the ASID bitmap. */
 145         bitmap_clear(asid_map, 0, NUM_USER_ASIDS);
 146         for_each_possible_cpu(i) {
 147                 asid = atomic64_xchg(&per_cpu(active_asids, i), 0);
 148                 /*
 149                  * If this CPU has already been through a
 150                  * rollover, but hasn't run another task in
 151                  * the meantime, we must preserve its reserved
 152                  * ASID, as this is the only trace we have of
 153                  * the process it is still running.
 154                  */
 155                 if (asid == 0)
 156                         asid = per_cpu(reserved_asids, i);
 157                 __set_bit(asid & ~ASID_MASK, asid_map);
 158                 per_cpu(reserved_asids, i) = asid;
 159         }
 160
 161         /* Queue a TLB invalidate and flush the I-cache if necessary. */
 162         cpumask_setall(&tlb_flush_pending);
 163
 164         if (icache_is_vivt_asid_tagged())
 165                 __flush_icache_all();
 166 }
 167
 168 static bool check_update_reserved_asid(u64 asid, u64 newasid)
 169 {
 170         int cpu;
 171         bool hit = false;
 172
 173         /*
 174          * Iterate over the set of reserved ASIDs looking for a match.
 175          * If we find one, then we can update our mm to use newasid
 176          * (i.e. the same ASID in the current generation) but we can't
 177          * exit the loop early, since we need to ensure that all copies
 178          * of the old ASID are updated to reflect the mm. Failure to do
 179          * so could result in us missing the reserved ASID in a future
 180          * generation.
 181          */
 182         for_each_possible_cpu(cpu) {
 183                 if (per_cpu(reserved_asids, cpu) == asid) {
 184                         hit = true;
 185                         per_cpu(reserved_asids, cpu) = newasid;
 186                 }
 187         }
 188
 189         return hit;
 190 }
 191
 192 static u64 new_context(struct mm_struct *mm, unsigned int cpu)
 193 {
 194         static u32 cur_idx = 1;
 195         u64 asid = atomic64_read(&mm->context.id);
 196         u64 generation = atomic64_read(&asid_generation);
 197
 198         if (asid != 0) {
 199                 u64 newasid = generation | (asid & ~ASID_MASK);
 200
 201                 /*
 202                  * If our current ASID was active during a rollover, we
 203                  * can continue to use it and this was just a false alarm.
 204                  */
 205                 if (check_update_reserved_asid(asid, newasid))
 206                         return newasid;
 207
 208                 /*
 209                  * We had a valid ASID in a previous life, so try to re-use
 210                  * it if possible.,
 211                  */
 212                 asid &= ~ASID_MASK;
 213                 if (!__test_and_set_bit(asid, asid_map))
 214                         return newasid;
 215         }
 216
 217         /*
 218          * Allocate a free ASID. If we can't find one, take a note of the
 219          * currently active ASIDs and mark the TLBs as requiring flushes.
 220          * We always count from ASID #1, as we reserve ASID #0 to switch
 221          * via TTBR0 and to avoid speculative page table walks from hitting
 222          * in any partial walk caches, which could be populated from
 223          * overlapping level-1 descriptors used to map both the module
 224          * area and the userspace stack.
 225          */
 226         asid = find_next_zero_bit(asid_map, NUM_USER_ASIDS, cur_idx);
 227         if (asid == NUM_USER_ASIDS) {
 228                 generation = atomic64_add_return(ASID_FIRST_VERSION,
 229                                                  &asid_generation);
 230                 flush_context(cpu);
 231                 asid = find_next_zero_bit(asid_map, NUM_USER_ASIDS, 1);
 232         }
 233
 234         __set_bit(asid, asid_map);
 235         cur_idx = asid;
 236         cpumask_clear(mm_cpumask(mm));
 237         return asid | generation;
 238 }
 239
 240 void check_and_switch_context(struct mm_struct *mm, struct task_struct *tsk)
 241 {
 242         unsigned long flags;
 243         unsigned int cpu = smp_processor_id();
 244         u64 asid;
 245
 246         if (unlikely(mm->context.vmalloc_seq != init_mm.context.vmalloc_seq))
 247                 __check_vmalloc_seq(mm);
 248
 249         /*
 250          * We cannot update the pgd and the ASID atomicly with classic
 251          * MMU, so switch exclusively to global mappings to avoid
 252          * speculative page table walking with the wrong TTBR.
 253          */
 254         cpu_set_reserved_ttbr0();
 255
 256         asid = atomic64_read(&mm->context.id);
 257         if (!((asid ^ atomic64_read(&asid_generation)) >> ASID_BITS)
 258             && atomic64_xchg(&per_cpu(active_asids, cpu), asid))
 259                 goto switch_mm_fastpath;
 260
 261         raw_spin_lock_irqsave(&cpu_asid_lock, flags);
 262         /* Check that our ASID belongs to the current generation. */
 263         asid = atomic64_read(&mm->context.id);
 264         if ((asid ^ atomic64_read(&asid_generation)) >> ASID_BITS) {
 265                 asid = new_context(mm, cpu);
 266                 atomic64_set(&mm->context.id, asid);
 267         }
 268
 269         if (cpumask_test_and_clear_cpu(cpu, &tlb_flush_pending)) {
 270                 local_flush_bp_all();
 271                 local_flush_tlb_all();
 272         }
 273
 274         atomic64_set(&per_cpu(active_asids, cpu), asid);
 275         cpumask_set_cpu(cpu, mm_cpumask(mm));
 276         raw_spin_unlock_irqrestore(&cpu_asid_lock, flags);
 277
 278 switch_mm_fastpath:
 279         cpu_switch_mm(mm->pgd, mm);
 280 }