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 set_reserved_asid_bits(void) 83 { 84 if (IS_ENABLED(CONFIG_QCOM_FALKOR_ERRATUM_1003) && 85 cpus_have_const_cap(ARM64_WORKAROUND_QCOM_FALKOR_E1003)) 86 __set_bit(FALKOR_RESERVED_ASID, asid_map); 87 } 88 89 static void flush_context(unsigned int cpu) 90 { 91 int i; 92 u64 asid; 93 94 /* Update the list of reserved ASIDs and the ASID bitmap. */ 95 bitmap_clear(asid_map, 0, NUM_USER_ASIDS); 96 97 set_reserved_asid_bits(); 98 99 /* 100 * Ensure the generation bump is observed before we xchg the 101 * active_asids. 102 */ 103 smp_wmb(); 104 105 for_each_possible_cpu(i) { 106 asid = atomic64_xchg_relaxed(&per_cpu(active_asids, i), 0); 107 /* 108 * If this CPU has already been through a 109 * rollover, but hasn't run another task in 110 * the meantime, we must preserve its reserved 111 * ASID, as this is the only trace we have of 112 * the process it is still running. 113 */ 114 if (asid == 0) 115 asid = per_cpu(reserved_asids, i); 116 __set_bit(asid & ~ASID_MASK, asid_map); 117 per_cpu(reserved_asids, i) = asid; 118 } 119 120 /* Queue a TLB invalidate and flush the I-cache if necessary. */ 121 cpumask_setall(&tlb_flush_pending); 122 } 123 124 static bool check_update_reserved_asid(u64 asid, u64 newasid) 125 { 126 int cpu; 127 bool hit = false; 128 129 /* 130 * Iterate over the set of reserved ASIDs looking for a match. 131 * If we find one, then we can update our mm to use newasid 132 * (i.e. the same ASID in the current generation) but we can't 133 * exit the loop early, since we need to ensure that all copies 134 * of the old ASID are updated to reflect the mm. Failure to do 135 * so could result in us missing the reserved ASID in a future 136 * generation. 137 */ 138 for_each_possible_cpu(cpu) { 139 if (per_cpu(reserved_asids, cpu) == asid) { 140 hit = true; 141 per_cpu(reserved_asids, cpu) = newasid; 142 } 143 } 144 145 return hit; 146 } 147 148 static u64 new_context(struct mm_struct *mm, unsigned int cpu) 149 { 150 static u32 cur_idx = 1; 151 u64 asid = atomic64_read(&mm->context.id); 152 u64 generation = atomic64_read(&asid_generation); 153 154 if (asid != 0) { 155 u64 newasid = generation | (asid & ~ASID_MASK); 156 157 /* 158 * If our current ASID was active during a rollover, we 159 * can continue to use it and this was just a false alarm. 160 */ 161 if (check_update_reserved_asid(asid, newasid)) 162 return newasid; 163 164 /* 165 * We had a valid ASID in a previous life, so try to re-use 166 * it if possible. 167 */ 168 asid &= ~ASID_MASK; 169 if (!__test_and_set_bit(asid, asid_map)) 170 return newasid; 171 } 172 173 /* 174 * Allocate a free ASID. If we can't find one, take a note of the 175 * currently active ASIDs and mark the TLBs as requiring flushes. 176 * We always count from ASID #1, as we use ASID #0 when setting a 177 * reserved TTBR0 for the init_mm. 178 */ 179 asid = find_next_zero_bit(asid_map, NUM_USER_ASIDS, cur_idx); 180 if (asid != NUM_USER_ASIDS) 181 goto set_asid; 182 183 /* We're out of ASIDs, so increment the global generation count */ 184 generation = atomic64_add_return_relaxed(ASID_FIRST_VERSION, 185 &asid_generation); 186 flush_context(cpu); 187 188 /* We have more ASIDs than CPUs, so this will always succeed */ 189 asid = find_next_zero_bit(asid_map, NUM_USER_ASIDS, 1); 190 191 set_asid: 192 __set_bit(asid, asid_map); 193 cur_idx = asid; 194 return asid | generation; 195 } 196 197 void check_and_switch_context(struct mm_struct *mm, unsigned int cpu) 198 { 199 unsigned long flags; 200 u64 asid; 201 202 asid = atomic64_read(&mm->context.id); 203 204 /* 205 * The memory ordering here is subtle. We rely on the control 206 * dependency between the generation read and the update of 207 * active_asids to ensure that we are synchronised with a 208 * parallel rollover (i.e. this pairs with the smp_wmb() in 209 * flush_context). 210 */ 211 if (!((asid ^ atomic64_read(&asid_generation)) >> asid_bits) 212 && atomic64_xchg_relaxed(&per_cpu(active_asids, cpu), asid)) 213 goto switch_mm_fastpath; 214 215 raw_spin_lock_irqsave(&cpu_asid_lock, flags); 216 /* Check that our ASID belongs to the current generation. */ 217 asid = atomic64_read(&mm->context.id); 218 if ((asid ^ atomic64_read(&asid_generation)) >> asid_bits) { 219 asid = new_context(mm, cpu); 220 atomic64_set(&mm->context.id, asid); 221 } 222 223 if (cpumask_test_and_clear_cpu(cpu, &tlb_flush_pending)) 224 local_flush_tlb_all(); 225 226 atomic64_set(&per_cpu(active_asids, cpu), asid); 227 raw_spin_unlock_irqrestore(&cpu_asid_lock, flags); 228 229 switch_mm_fastpath: 230 /* 231 * Defer TTBR0_EL1 setting for user threads to uaccess_enable() when 232 * emulating PAN. 233 */ 234 if (!system_uses_ttbr0_pan()) 235 cpu_switch_mm(mm->pgd, mm); 236 } 237 238 static int asids_init(void) 239 { 240 asid_bits = get_cpu_asid_bits(); 241 /* 242 * Expect allocation after rollover to fail if we don't have at least 243 * one more ASID than CPUs. ASID #0 is reserved for init_mm. 244 */ 245 WARN_ON(NUM_USER_ASIDS - 1 <= num_possible_cpus()); 246 atomic64_set(&asid_generation, ASID_FIRST_VERSION); 247 asid_map = kzalloc(BITS_TO_LONGS(NUM_USER_ASIDS) * sizeof(*asid_map), 248 GFP_KERNEL); 249 if (!asid_map) 250 panic("Failed to allocate bitmap for %lu ASIDs\n", 251 NUM_USER_ASIDS); 252 253 set_reserved_asid_bits(); 254 255 pr_info("ASID allocator initialised with %lu entries\n", NUM_USER_ASIDS); 256 return 0; 257 } 258 early_initcall(asids_init); 259