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/tlbflush.h> 28 29 static u32 asid_bits; 30 static DEFINE_RAW_SPINLOCK(cpu_asid_lock); 31 32 static atomic64_t asid_generation; 33 static unsigned long *asid_map; 34 35 static DEFINE_PER_CPU(atomic64_t, active_asids); 36 static DEFINE_PER_CPU(u64, reserved_asids); 37 static cpumask_t tlb_flush_pending; 38 39 #define ASID_MASK (~GENMASK(asid_bits - 1, 0)) 40 #define ASID_FIRST_VERSION (1UL << asid_bits) 41 #define NUM_USER_ASIDS ASID_FIRST_VERSION 42 43 static void flush_context(unsigned int cpu) 44 { 45 int i; 46 u64 asid; 47 48 /* Update the list of reserved ASIDs and the ASID bitmap. */ 49 bitmap_clear(asid_map, 0, NUM_USER_ASIDS); 50 51 /* 52 * Ensure the generation bump is observed before we xchg the 53 * active_asids. 54 */ 55 smp_wmb(); 56 57 for_each_possible_cpu(i) { 58 asid = atomic64_xchg_relaxed(&per_cpu(active_asids, i), 0); 59 /* 60 * If this CPU has already been through a 61 * rollover, but hasn't run another task in 62 * the meantime, we must preserve its reserved 63 * ASID, as this is the only trace we have of 64 * the process it is still running. 65 */ 66 if (asid == 0) 67 asid = per_cpu(reserved_asids, i); 68 __set_bit(asid & ~ASID_MASK, asid_map); 69 per_cpu(reserved_asids, i) = asid; 70 } 71 72 /* Queue a TLB invalidate and flush the I-cache if necessary. */ 73 cpumask_setall(&tlb_flush_pending); 74 75 if (icache_is_aivivt()) 76 __flush_icache_all(); 77 } 78 79 static bool check_update_reserved_asid(u64 asid, u64 newasid) 80 { 81 int cpu; 82 bool hit = false; 83 84 /* 85 * Iterate over the set of reserved ASIDs looking for a match. 86 * If we find one, then we can update our mm to use newasid 87 * (i.e. the same ASID in the current generation) but we can't 88 * exit the loop early, since we need to ensure that all copies 89 * of the old ASID are updated to reflect the mm. Failure to do 90 * so could result in us missing the reserved ASID in a future 91 * generation. 92 */ 93 for_each_possible_cpu(cpu) { 94 if (per_cpu(reserved_asids, cpu) == asid) { 95 hit = true; 96 per_cpu(reserved_asids, cpu) = newasid; 97 } 98 } 99 100 return hit; 101 } 102 103 static u64 new_context(struct mm_struct *mm, unsigned int cpu) 104 { 105 static u32 cur_idx = 1; 106 u64 asid = atomic64_read(&mm->context.id); 107 u64 generation = atomic64_read(&asid_generation); 108 109 if (asid != 0) { 110 u64 newasid = generation | (asid & ~ASID_MASK); 111 112 /* 113 * If our current ASID was active during a rollover, we 114 * can continue to use it and this was just a false alarm. 115 */ 116 if (check_update_reserved_asid(asid, newasid)) 117 return newasid; 118 119 /* 120 * We had a valid ASID in a previous life, so try to re-use 121 * it if possible. 122 */ 123 asid &= ~ASID_MASK; 124 if (!__test_and_set_bit(asid, asid_map)) 125 return newasid; 126 } 127 128 /* 129 * Allocate a free ASID. If we can't find one, take a note of the 130 * currently active ASIDs and mark the TLBs as requiring flushes. 131 * We always count from ASID #1, as we use ASID #0 when setting a 132 * reserved TTBR0 for the init_mm. 133 */ 134 asid = find_next_zero_bit(asid_map, NUM_USER_ASIDS, cur_idx); 135 if (asid != NUM_USER_ASIDS) 136 goto set_asid; 137 138 /* We're out of ASIDs, so increment the global generation count */ 139 generation = atomic64_add_return_relaxed(ASID_FIRST_VERSION, 140 &asid_generation); 141 flush_context(cpu); 142 143 /* We have at least 1 ASID per CPU, so this will always succeed */ 144 asid = find_next_zero_bit(asid_map, NUM_USER_ASIDS, 1); 145 146 set_asid: 147 __set_bit(asid, asid_map); 148 cur_idx = asid; 149 return asid | generation; 150 } 151 152 void check_and_switch_context(struct mm_struct *mm, unsigned int cpu) 153 { 154 unsigned long flags; 155 u64 asid; 156 157 asid = atomic64_read(&mm->context.id); 158 159 /* 160 * The memory ordering here is subtle. We rely on the control 161 * dependency between the generation read and the update of 162 * active_asids to ensure that we are synchronised with a 163 * parallel rollover (i.e. this pairs with the smp_wmb() in 164 * flush_context). 165 */ 166 if (!((asid ^ atomic64_read(&asid_generation)) >> asid_bits) 167 && atomic64_xchg_relaxed(&per_cpu(active_asids, cpu), asid)) 168 goto switch_mm_fastpath; 169 170 raw_spin_lock_irqsave(&cpu_asid_lock, flags); 171 /* Check that our ASID belongs to the current generation. */ 172 asid = atomic64_read(&mm->context.id); 173 if ((asid ^ atomic64_read(&asid_generation)) >> asid_bits) { 174 asid = new_context(mm, cpu); 175 atomic64_set(&mm->context.id, asid); 176 } 177 178 if (cpumask_test_and_clear_cpu(cpu, &tlb_flush_pending)) 179 local_flush_tlb_all(); 180 181 atomic64_set(&per_cpu(active_asids, cpu), asid); 182 raw_spin_unlock_irqrestore(&cpu_asid_lock, flags); 183 184 switch_mm_fastpath: 185 cpu_switch_mm(mm->pgd, mm); 186 } 187 188 static int asids_init(void) 189 { 190 int fld = cpuid_feature_extract_field(read_cpuid(ID_AA64MMFR0_EL1), 4); 191 192 switch (fld) { 193 default: 194 pr_warn("Unknown ASID size (%d); assuming 8-bit\n", fld); 195 /* Fallthrough */ 196 case 0: 197 asid_bits = 8; 198 break; 199 case 2: 200 asid_bits = 16; 201 } 202 203 /* If we end up with more CPUs than ASIDs, expect things to crash */ 204 WARN_ON(NUM_USER_ASIDS < num_possible_cpus()); 205 atomic64_set(&asid_generation, ASID_FIRST_VERSION); 206 asid_map = kzalloc(BITS_TO_LONGS(NUM_USER_ASIDS) * sizeof(*asid_map), 207 GFP_KERNEL); 208 if (!asid_map) 209 panic("Failed to allocate bitmap for %lu ASIDs\n", 210 NUM_USER_ASIDS); 211 212 pr_info("ASID allocator initialised with %lu entries\n", NUM_USER_ASIDS); 213 return 0; 214 } 215 early_initcall(asids_init); 216