1 /* 2 * Based on arch/arm/mm/context.c 3 * 4 * Copyright (C) 2002-2003 Deep Blue Solutions Ltd, all rights reserved. 5 * Copyright (C) 2012 ARM Ltd. 6 * 7 * This program is free software; you can redistribute it and/or modify 8 * it under the terms of the GNU General Public License version 2 as 9 * published by the Free Software Foundation. 10 * 11 * This program is distributed in the hope that it will be useful, 12 * but WITHOUT ANY WARRANTY; without even the implied warranty of 13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 14 * GNU General Public License for more details. 15 * 16 * You should have received a copy of the GNU General Public License 17 * along with this program. If not, see <http://www.gnu.org/licenses/>. 18 */ 19 20 #include <linux/bitops.h> 21 #include <linux/sched.h> 22 #include <linux/slab.h> 23 #include <linux/mm.h> 24 25 #include <asm/cpufeature.h> 26 #include <asm/mmu_context.h> 27 #include <asm/smp.h> 28 #include <asm/tlbflush.h> 29 30 static u32 asid_bits; 31 static DEFINE_RAW_SPINLOCK(cpu_asid_lock); 32 33 static atomic64_t asid_generation; 34 static unsigned long *asid_map; 35 36 static DEFINE_PER_CPU(atomic64_t, active_asids); 37 static DEFINE_PER_CPU(u64, reserved_asids); 38 static cpumask_t tlb_flush_pending; 39 40 #define ASID_MASK (~GENMASK(asid_bits - 1, 0)) 41 #define ASID_FIRST_VERSION (1UL << asid_bits) 42 #define NUM_USER_ASIDS ASID_FIRST_VERSION 43 44 /* Get the ASIDBits supported by the current CPU */ 45 static u32 get_cpu_asid_bits(void) 46 { 47 u32 asid; 48 int fld = cpuid_feature_extract_unsigned_field(read_cpuid(ID_AA64MMFR0_EL1), 49 ID_AA64MMFR0_ASID_SHIFT); 50 51 switch (fld) { 52 default: 53 pr_warn("CPU%d: Unknown ASID size (%d); assuming 8-bit\n", 54 smp_processor_id(), fld); 55 /* Fallthrough */ 56 case 0: 57 asid = 8; 58 break; 59 case 2: 60 asid = 16; 61 } 62 63 return asid; 64 } 65 66 /* Check if the current cpu's ASIDBits is compatible with asid_bits */ 67 void verify_cpu_asid_bits(void) 68 { 69 u32 asid = get_cpu_asid_bits(); 70 71 if (asid < asid_bits) { 72 /* 73 * We cannot decrease the ASID size at runtime, so panic if we support 74 * fewer ASID bits than the boot CPU. 75 */ 76 pr_crit("CPU%d: smaller ASID size(%u) than boot CPU (%u)\n", 77 smp_processor_id(), asid, asid_bits); 78 cpu_panic_kernel(); 79 } 80 } 81 82 static void flush_context(unsigned int cpu) 83 { 84 int i; 85 u64 asid; 86 87 /* Update the list of reserved ASIDs and the ASID bitmap. */ 88 bitmap_clear(asid_map, 0, NUM_USER_ASIDS); 89 90 /* 91 * Ensure the generation bump is observed before we xchg the 92 * active_asids. 93 */ 94 smp_wmb(); 95 96 for_each_possible_cpu(i) { 97 asid = atomic64_xchg_relaxed(&per_cpu(active_asids, i), 0); 98 /* 99 * If this CPU has already been through a 100 * rollover, but hasn't run another task in 101 * the meantime, we must preserve its reserved 102 * ASID, as this is the only trace we have of 103 * the process it is still running. 104 */ 105 if (asid == 0) 106 asid = per_cpu(reserved_asids, i); 107 __set_bit(asid & ~ASID_MASK, asid_map); 108 per_cpu(reserved_asids, i) = asid; 109 } 110 111 /* Queue a TLB invalidate and flush the I-cache if necessary. */ 112 cpumask_setall(&tlb_flush_pending); 113 114 if (icache_is_aivivt()) 115 __flush_icache_all(); 116 } 117 118 static bool check_update_reserved_asid(u64 asid, u64 newasid) 119 { 120 int cpu; 121 bool hit = false; 122 123 /* 124 * Iterate over the set of reserved ASIDs looking for a match. 125 * If we find one, then we can update our mm to use newasid 126 * (i.e. the same ASID in the current generation) but we can't 127 * exit the loop early, since we need to ensure that all copies 128 * of the old ASID are updated to reflect the mm. Failure to do 129 * so could result in us missing the reserved ASID in a future 130 * generation. 131 */ 132 for_each_possible_cpu(cpu) { 133 if (per_cpu(reserved_asids, cpu) == asid) { 134 hit = true; 135 per_cpu(reserved_asids, cpu) = newasid; 136 } 137 } 138 139 return hit; 140 } 141 142 static u64 new_context(struct mm_struct *mm, unsigned int cpu) 143 { 144 static u32 cur_idx = 1; 145 u64 asid = atomic64_read(&mm->context.id); 146 u64 generation = atomic64_read(&asid_generation); 147 148 if (asid != 0) { 149 u64 newasid = generation | (asid & ~ASID_MASK); 150 151 /* 152 * If our current ASID was active during a rollover, we 153 * can continue to use it and this was just a false alarm. 154 */ 155 if (check_update_reserved_asid(asid, newasid)) 156 return newasid; 157 158 /* 159 * We had a valid ASID in a previous life, so try to re-use 160 * it if possible. 161 */ 162 asid &= ~ASID_MASK; 163 if (!__test_and_set_bit(asid, asid_map)) 164 return newasid; 165 } 166 167 /* 168 * Allocate a free ASID. If we can't find one, take a note of the 169 * currently active ASIDs and mark the TLBs as requiring flushes. 170 * We always count from ASID #1, as we use ASID #0 when setting a 171 * reserved TTBR0 for the init_mm. 172 */ 173 asid = find_next_zero_bit(asid_map, NUM_USER_ASIDS, cur_idx); 174 if (asid != NUM_USER_ASIDS) 175 goto set_asid; 176 177 /* We're out of ASIDs, so increment the global generation count */ 178 generation = atomic64_add_return_relaxed(ASID_FIRST_VERSION, 179 &asid_generation); 180 flush_context(cpu); 181 182 /* We have at least 1 ASID per CPU, so this will always succeed */ 183 asid = find_next_zero_bit(asid_map, NUM_USER_ASIDS, 1); 184 185 set_asid: 186 __set_bit(asid, asid_map); 187 cur_idx = asid; 188 return asid | generation; 189 } 190 191 void check_and_switch_context(struct mm_struct *mm, unsigned int cpu) 192 { 193 unsigned long flags; 194 u64 asid; 195 196 asid = atomic64_read(&mm->context.id); 197 198 /* 199 * The memory ordering here is subtle. We rely on the control 200 * dependency between the generation read and the update of 201 * active_asids to ensure that we are synchronised with a 202 * parallel rollover (i.e. this pairs with the smp_wmb() in 203 * flush_context). 204 */ 205 if (!((asid ^ atomic64_read(&asid_generation)) >> asid_bits) 206 && atomic64_xchg_relaxed(&per_cpu(active_asids, cpu), asid)) 207 goto switch_mm_fastpath; 208 209 raw_spin_lock_irqsave(&cpu_asid_lock, flags); 210 /* Check that our ASID belongs to the current generation. */ 211 asid = atomic64_read(&mm->context.id); 212 if ((asid ^ atomic64_read(&asid_generation)) >> asid_bits) { 213 asid = new_context(mm, cpu); 214 atomic64_set(&mm->context.id, asid); 215 } 216 217 if (cpumask_test_and_clear_cpu(cpu, &tlb_flush_pending)) 218 local_flush_tlb_all(); 219 220 atomic64_set(&per_cpu(active_asids, cpu), asid); 221 raw_spin_unlock_irqrestore(&cpu_asid_lock, flags); 222 223 switch_mm_fastpath: 224 cpu_switch_mm(mm->pgd, mm); 225 } 226 227 static int asids_init(void) 228 { 229 asid_bits = get_cpu_asid_bits(); 230 /* If we end up with more CPUs than ASIDs, expect things to crash */ 231 WARN_ON(NUM_USER_ASIDS < num_possible_cpus()); 232 atomic64_set(&asid_generation, ASID_FIRST_VERSION); 233 asid_map = kzalloc(BITS_TO_LONGS(NUM_USER_ASIDS) * sizeof(*asid_map), 234 GFP_KERNEL); 235 if (!asid_map) 236 panic("Failed to allocate bitmap for %lu ASIDs\n", 237 NUM_USER_ASIDS); 238 239 pr_info("ASID allocator initialised with %lu entries\n", NUM_USER_ASIDS); 240 return 0; 241 } 242 early_initcall(asids_init); 243