1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * Generic ASID allocator.
4 *
5 * Based on arch/arm/mm/context.c
6 *
7 * Copyright (C) 2002-2003 Deep Blue Solutions Ltd, all rights reserved.
8 * Copyright (C) 2012 ARM Ltd.
9 */
10
11 #include <linux/slab.h>
12 #include <linux/mm_types.h>
13
14 #include <asm/asid.h>
15
16 #define reserved_asid(info, cpu) *per_cpu_ptr((info)->reserved, cpu)
17
18 #define ASID_MASK(info) (~GENMASK((info)->bits - 1, 0))
19 #define ASID_FIRST_VERSION(info) (1UL << ((info)->bits))
20
21 #define asid2idx(info, asid) (((asid) & ~ASID_MASK(info)) >> (info)->ctxt_shift)
22 #define idx2asid(info, idx) (((idx) << (info)->ctxt_shift) & ~ASID_MASK(info))
23
24 static void flush_context(struct asid_info *info)
25 {
26 int i;
27 u64 asid;
28
29 /* Update the list of reserved ASIDs and the ASID bitmap. */
30 bitmap_zero(info->map, NUM_CTXT_ASIDS(info));
31
32 for_each_possible_cpu(i) {
33 asid = atomic64_xchg_relaxed(&active_asid(info, i), 0);
34 /*
35 * If this CPU has already been through a
36 * rollover, but hasn't run another task in
37 * the meantime, we must preserve its reserved
38 * ASID, as this is the only trace we have of
39 * the process it is still running.
40 */
41 if (asid == 0)
42 asid = reserved_asid(info, i);
43 __set_bit(asid2idx(info, asid), info->map);
44 reserved_asid(info, i) = asid;
45 }
46
47 /*
48 * Queue a TLB invalidation for each CPU to perform on next
49 * context-switch
50 */
51 cpumask_setall(&info->flush_pending);
52 }
53
54 static bool check_update_reserved_asid(struct asid_info *info, u64 asid,
55 u64 newasid)
56 {
57 int cpu;
58 bool hit = false;
59
60 /*
61 * Iterate over the set of reserved ASIDs looking for a match.
62 * If we find one, then we can update our mm to use newasid
63 * (i.e. the same ASID in the current generation) but we can't
64 * exit the loop early, since we need to ensure that all copies
65 * of the old ASID are updated to reflect the mm. Failure to do
66 * so could result in us missing the reserved ASID in a future
67 * generation.
68 */
69 for_each_possible_cpu(cpu) {
70 if (reserved_asid(info, cpu) == asid) {
71 hit = true;
72 reserved_asid(info, cpu) = newasid;
73 }
74 }
75
76 return hit;
77 }
78
79 static u64 new_context(struct asid_info *info, atomic64_t *pasid,
80 struct mm_struct *mm)
81 {
82 static u32 cur_idx = 1;
83 u64 asid = atomic64_read(pasid);
84 u64 generation = atomic64_read(&info->generation);
85
86 if (asid != 0) {
87 u64 newasid = generation | (asid & ~ASID_MASK(info));
88
89 /*
90 * If our current ASID was active during a rollover, we
91 * can continue to use it and this was just a false alarm.
92 */
93 if (check_update_reserved_asid(info, asid, newasid))
94 return newasid;
95
96 /*
97 * We had a valid ASID in a previous life, so try to re-use
98 * it if possible.
99 */
100 if (!__test_and_set_bit(asid2idx(info, asid), info->map))
101 return newasid;
102 }
103
104 /*
105 * Allocate a free ASID. If we can't find one, take a note of the
106 * currently active ASIDs and mark the TLBs as requiring flushes. We
107 * always count from ASID #2 (index 1), as we use ASID #0 when setting
108 * a reserved TTBR0 for the init_mm and we allocate ASIDs in even/odd
109 * pairs.
110 */
111 asid = find_next_zero_bit(info->map, NUM_CTXT_ASIDS(info), cur_idx);
112 if (asid != NUM_CTXT_ASIDS(info))
113 goto set_asid;
114
115 /* We're out of ASIDs, so increment the global generation count */
116 generation = atomic64_add_return_relaxed(ASID_FIRST_VERSION(info),
117 &info->generation);
118 flush_context(info);
119
120 /* We have more ASIDs than CPUs, so this will always succeed */
121 asid = find_next_zero_bit(info->map, NUM_CTXT_ASIDS(info), 1);
122
123 set_asid:
124 __set_bit(asid, info->map);
125 cur_idx = asid;
126 cpumask_clear(mm_cpumask(mm));
127 return idx2asid(info, asid) | generation;
128 }
129
130 /*
131 * Generate a new ASID for the context.
132 *
133 * @pasid: Pointer to the current ASID batch allocated. It will be updated
134 * with the new ASID batch.
135 * @cpu: current CPU ID. Must have been acquired through get_cpu()
136 */
137 void asid_new_context(struct asid_info *info, atomic64_t *pasid,
138 unsigned int cpu, struct mm_struct *mm)
139 {
140 unsigned long flags;
141 u64 asid;
142
143 raw_spin_lock_irqsave(&info->lock, flags);
144 /* Check that our ASID belongs to the current generation. */
145 asid = atomic64_read(pasid);
146 if ((asid ^ atomic64_read(&info->generation)) >> info->bits) {
147 asid = new_context(info, pasid, mm);
148 atomic64_set(pasid, asid);
149 }
150
151 if (cpumask_test_and_clear_cpu(cpu, &info->flush_pending))
152 info->flush_cpu_ctxt_cb();
153
154 atomic64_set(&active_asid(info, cpu), asid);
155 cpumask_set_cpu(cpu, mm_cpumask(mm));
156 raw_spin_unlock_irqrestore(&info->lock, flags);
157 }
158
159 /*
160 * Initialize the ASID allocator
161 *
162 * @info: Pointer to the asid allocator structure
163 * @bits: Number of ASIDs available
164 * @asid_per_ctxt: Number of ASIDs to allocate per-context. ASIDs are
165 * allocated contiguously for a given context. This value should be a power of
166 * 2.
167 */
168 int asid_allocator_init(struct asid_info *info,
169 u32 bits, unsigned int asid_per_ctxt,
170 void (*flush_cpu_ctxt_cb)(void))
171 {
172 info->bits = bits;
173 info->ctxt_shift = ilog2(asid_per_ctxt);
174 info->flush_cpu_ctxt_cb = flush_cpu_ctxt_cb;
175 /*
176 * Expect allocation after rollover to fail if we don't have at least
177 * one more ASID than CPUs. ASID #0 is always reserved.
178 */
179 WARN_ON(NUM_CTXT_ASIDS(info) - 1 <= num_possible_cpus());
180 atomic64_set(&info->generation, ASID_FIRST_VERSION(info));
181 info->map = bitmap_zalloc(NUM_CTXT_ASIDS(info), GFP_KERNEL);
182 if (!info->map)
183 return -ENOMEM;
184
185 raw_spin_lock_init(&info->lock);
186
187 return 0;
188 }
189
Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.