1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * Based on arch/arm/mm/context.c
4 *
5 * Copyright (C) 2002-2003 Deep Blue Solutions Ltd, all rights reserved.
6 * Copyright (C) 2012 ARM Ltd.
7 */
8
9 #include <linux/bitfield.h>
10 #include <linux/bitops.h>
11 #include <linux/sched.h>
12 #include <linux/slab.h>
13 #include <linux/mm.h>
14
15 #include <asm/cpufeature.h>
16 #include <asm/mmu_context.h>
17 #include <asm/smp.h>
18 #include <asm/tlbflush.h>
19
20 static u32 asid_bits;
21 static DEFINE_RAW_SPINLOCK(cpu_asid_lock);
22
23 static atomic64_t asid_generation;
24 static unsigned long *asid_map;
25
26 static DEFINE_PER_CPU(atomic64_t, active_asids);
27 static DEFINE_PER_CPU(u64, reserved_asids);
28 static cpumask_t tlb_flush_pending;
29
30 static unsigned long max_pinned_asids;
31 static unsigned long nr_pinned_asids;
32 static unsigned long *pinned_asid_map;
33
34 #define ASID_MASK (~GENMASK(asid_bits - 1, 0))
35 #define ASID_FIRST_VERSION (1UL << asid_bits)
36
37 #define NUM_USER_ASIDS ASID_FIRST_VERSION
38 #define asid2idx(asid) ((asid) & ~ASID_MASK)
39 #define idx2asid(idx) asid2idx(idx)
40
41 /* Get the ASIDBits supported by the current CPU */
get_cpu_asid_bits(void)42 static u32 get_cpu_asid_bits(void)
43 {
44 u32 asid;
45 int fld = cpuid_feature_extract_unsigned_field(read_cpuid(ID_AA64MMFR0_EL1),
46 ID_AA64MMFR0_ASID_SHIFT);
47
48 switch (fld) {
49 default:
50 pr_warn("CPU%d: Unknown ASID size (%d); assuming 8-bit\n",
51 smp_processor_id(), fld);
52 fallthrough;
53 case 0:
54 asid = 8;
55 break;
56 case 2:
57 asid = 16;
58 }
59
60 return asid;
61 }
62
63 /* Check if the current cpu's ASIDBits is compatible with asid_bits */
verify_cpu_asid_bits(void)64 void verify_cpu_asid_bits(void)
65 {
66 u32 asid = get_cpu_asid_bits();
67
68 if (asid < asid_bits) {
69 /*
70 * We cannot decrease the ASID size at runtime, so panic if we support
71 * fewer ASID bits than the boot CPU.
72 */
73 pr_crit("CPU%d: smaller ASID size(%u) than boot CPU (%u)\n",
74 smp_processor_id(), asid, asid_bits);
75 cpu_panic_kernel();
76 }
77 }
78
set_kpti_asid_bits(unsigned long * map)79 static void set_kpti_asid_bits(unsigned long *map)
80 {
81 unsigned int len = BITS_TO_LONGS(NUM_USER_ASIDS) * sizeof(unsigned long);
82 /*
83 * In case of KPTI kernel/user ASIDs are allocated in
84 * pairs, the bottom bit distinguishes the two: if it
85 * is set, then the ASID will map only userspace. Thus
86 * mark even as reserved for kernel.
87 */
88 memset(map, 0xaa, len);
89 }
90
set_reserved_asid_bits(void)91 static void set_reserved_asid_bits(void)
92 {
93 if (pinned_asid_map)
94 bitmap_copy(asid_map, pinned_asid_map, NUM_USER_ASIDS);
95 else if (arm64_kernel_unmapped_at_el0())
96 set_kpti_asid_bits(asid_map);
97 else
98 bitmap_clear(asid_map, 0, NUM_USER_ASIDS);
99 }
100
101 #define asid_gen_match(asid) \
102 (!(((asid) ^ atomic64_read(&asid_generation)) >> asid_bits))
103
flush_context(void)104 static void flush_context(void)
105 {
106 int i;
107 u64 asid;
108
109 /* Update the list of reserved ASIDs and the ASID bitmap. */
110 set_reserved_asid_bits();
111
112 for_each_possible_cpu(i) {
113 asid = atomic64_xchg_relaxed(&per_cpu(active_asids, i), 0);
114 /*
115 * If this CPU has already been through a
116 * rollover, but hasn't run another task in
117 * the meantime, we must preserve its reserved
118 * ASID, as this is the only trace we have of
119 * the process it is still running.
120 */
121 if (asid == 0)
122 asid = per_cpu(reserved_asids, i);
123 __set_bit(asid2idx(asid), asid_map);
124 per_cpu(reserved_asids, i) = asid;
125 }
126
127 /*
128 * Queue a TLB invalidation for each CPU to perform on next
129 * context-switch
130 */
131 cpumask_setall(&tlb_flush_pending);
132 }
133
check_update_reserved_asid(u64 asid,u64 newasid)134 static bool check_update_reserved_asid(u64 asid, u64 newasid)
135 {
136 int cpu;
137 bool hit = false;
138
139 /*
140 * Iterate over the set of reserved ASIDs looking for a match.
141 * If we find one, then we can update our mm to use newasid
142 * (i.e. the same ASID in the current generation) but we can't
143 * exit the loop early, since we need to ensure that all copies
144 * of the old ASID are updated to reflect the mm. Failure to do
145 * so could result in us missing the reserved ASID in a future
146 * generation.
147 */
148 for_each_possible_cpu(cpu) {
149 if (per_cpu(reserved_asids, cpu) == asid) {
150 hit = true;
151 per_cpu(reserved_asids, cpu) = newasid;
152 }
153 }
154
155 return hit;
156 }
157
new_context(struct mm_struct * mm)158 static u64 new_context(struct mm_struct *mm)
159 {
160 static u32 cur_idx = 1;
161 u64 asid = atomic64_read(&mm->context.id);
162 u64 generation = atomic64_read(&asid_generation);
163
164 if (asid != 0) {
165 u64 newasid = generation | (asid & ~ASID_MASK);
166
167 /*
168 * If our current ASID was active during a rollover, we
169 * can continue to use it and this was just a false alarm.
170 */
171 if (check_update_reserved_asid(asid, newasid))
172 return newasid;
173
174 /*
175 * If it is pinned, we can keep using it. Note that reserved
176 * takes priority, because even if it is also pinned, we need to
177 * update the generation into the reserved_asids.
178 */
179 if (refcount_read(&mm->context.pinned))
180 return newasid;
181
182 /*
183 * We had a valid ASID in a previous life, so try to re-use
184 * it if possible.
185 */
186 if (!__test_and_set_bit(asid2idx(asid), asid_map))
187 return newasid;
188 }
189
190 /*
191 * Allocate a free ASID. If we can't find one, take a note of the
192 * currently active ASIDs and mark the TLBs as requiring flushes. We
193 * always count from ASID #2 (index 1), as we use ASID #0 when setting
194 * a reserved TTBR0 for the init_mm and we allocate ASIDs in even/odd
195 * pairs.
196 */
197 asid = find_next_zero_bit(asid_map, NUM_USER_ASIDS, cur_idx);
198 if (asid != NUM_USER_ASIDS)
199 goto set_asid;
200
201 /* We're out of ASIDs, so increment the global generation count */
202 generation = atomic64_add_return_relaxed(ASID_FIRST_VERSION,
203 &asid_generation);
204 flush_context();
205
206 /* We have more ASIDs than CPUs, so this will always succeed */
207 asid = find_next_zero_bit(asid_map, NUM_USER_ASIDS, 1);
208
209 set_asid:
210 __set_bit(asid, asid_map);
211 cur_idx = asid;
212 return idx2asid(asid) | generation;
213 }
214
check_and_switch_context(struct mm_struct * mm)215 void check_and_switch_context(struct mm_struct *mm)
216 {
217 unsigned long flags;
218 unsigned int cpu;
219 u64 asid, old_active_asid;
220
221 if (system_supports_cnp())
222 cpu_set_reserved_ttbr0();
223
224 asid = atomic64_read(&mm->context.id);
225
226 /*
227 * The memory ordering here is subtle.
228 * If our active_asids is non-zero and the ASID matches the current
229 * generation, then we update the active_asids entry with a relaxed
230 * cmpxchg. Racing with a concurrent rollover means that either:
231 *
232 * - We get a zero back from the cmpxchg and end up waiting on the
233 * lock. Taking the lock synchronises with the rollover and so
234 * we are forced to see the updated generation.
235 *
236 * - We get a valid ASID back from the cmpxchg, which means the
237 * relaxed xchg in flush_context will treat us as reserved
238 * because atomic RmWs are totally ordered for a given location.
239 */
240 old_active_asid = atomic64_read(this_cpu_ptr(&active_asids));
241 if (old_active_asid && asid_gen_match(asid) &&
242 atomic64_cmpxchg_relaxed(this_cpu_ptr(&active_asids),
243 old_active_asid, asid))
244 goto switch_mm_fastpath;
245
246 raw_spin_lock_irqsave(&cpu_asid_lock, flags);
247 /* Check that our ASID belongs to the current generation. */
248 asid = atomic64_read(&mm->context.id);
249 if (!asid_gen_match(asid)) {
250 asid = new_context(mm);
251 atomic64_set(&mm->context.id, asid);
252 }
253
254 cpu = smp_processor_id();
255 if (cpumask_test_and_clear_cpu(cpu, &tlb_flush_pending))
256 local_flush_tlb_all();
257
258 atomic64_set(this_cpu_ptr(&active_asids), asid);
259 raw_spin_unlock_irqrestore(&cpu_asid_lock, flags);
260
261 switch_mm_fastpath:
262
263 arm64_apply_bp_hardening();
264
265 /*
266 * Defer TTBR0_EL1 setting for user threads to uaccess_enable() when
267 * emulating PAN.
268 */
269 if (!system_uses_ttbr0_pan())
270 cpu_switch_mm(mm->pgd, mm);
271 }
272
arm64_mm_context_get(struct mm_struct * mm)273 unsigned long arm64_mm_context_get(struct mm_struct *mm)
274 {
275 unsigned long flags;
276 u64 asid;
277
278 if (!pinned_asid_map)
279 return 0;
280
281 raw_spin_lock_irqsave(&cpu_asid_lock, flags);
282
283 asid = atomic64_read(&mm->context.id);
284
285 if (refcount_inc_not_zero(&mm->context.pinned))
286 goto out_unlock;
287
288 if (nr_pinned_asids >= max_pinned_asids) {
289 asid = 0;
290 goto out_unlock;
291 }
292
293 if (!asid_gen_match(asid)) {
294 /*
295 * We went through one or more rollover since that ASID was
296 * used. Ensure that it is still valid, or generate a new one.
297 */
298 asid = new_context(mm);
299 atomic64_set(&mm->context.id, asid);
300 }
301
302 nr_pinned_asids++;
303 __set_bit(asid2idx(asid), pinned_asid_map);
304 refcount_set(&mm->context.pinned, 1);
305
306 out_unlock:
307 raw_spin_unlock_irqrestore(&cpu_asid_lock, flags);
308
309 asid &= ~ASID_MASK;
310
311 /* Set the equivalent of USER_ASID_BIT */
312 if (asid && arm64_kernel_unmapped_at_el0())
313 asid |= 1;
314
315 return asid;
316 }
317 EXPORT_SYMBOL_GPL(arm64_mm_context_get);
318
arm64_mm_context_put(struct mm_struct * mm)319 void arm64_mm_context_put(struct mm_struct *mm)
320 {
321 unsigned long flags;
322 u64 asid = atomic64_read(&mm->context.id);
323
324 if (!pinned_asid_map)
325 return;
326
327 raw_spin_lock_irqsave(&cpu_asid_lock, flags);
328
329 if (refcount_dec_and_test(&mm->context.pinned)) {
330 __clear_bit(asid2idx(asid), pinned_asid_map);
331 nr_pinned_asids--;
332 }
333
334 raw_spin_unlock_irqrestore(&cpu_asid_lock, flags);
335 }
336 EXPORT_SYMBOL_GPL(arm64_mm_context_put);
337
338 /* Errata workaround post TTBRx_EL1 update. */
post_ttbr_update_workaround(void)339 asmlinkage void post_ttbr_update_workaround(void)
340 {
341 if (!IS_ENABLED(CONFIG_CAVIUM_ERRATUM_27456))
342 return;
343
344 asm(ALTERNATIVE("nop; nop; nop",
345 "ic iallu; dsb nsh; isb",
346 ARM64_WORKAROUND_CAVIUM_27456));
347 }
348
cpu_do_switch_mm(phys_addr_t pgd_phys,struct mm_struct * mm)349 void cpu_do_switch_mm(phys_addr_t pgd_phys, struct mm_struct *mm)
350 {
351 unsigned long ttbr1 = read_sysreg(ttbr1_el1);
352 unsigned long asid = ASID(mm);
353 unsigned long ttbr0 = phys_to_ttbr(pgd_phys);
354
355 /* Skip CNP for the reserved ASID */
356 if (system_supports_cnp() && asid)
357 ttbr0 |= TTBR_CNP_BIT;
358
359 /* SW PAN needs a copy of the ASID in TTBR0 for entry */
360 if (IS_ENABLED(CONFIG_ARM64_SW_TTBR0_PAN))
361 ttbr0 |= FIELD_PREP(TTBR_ASID_MASK, asid);
362
363 /* Set ASID in TTBR1 since TCR.A1 is set */
364 ttbr1 &= ~TTBR_ASID_MASK;
365 ttbr1 |= FIELD_PREP(TTBR_ASID_MASK, asid);
366
367 write_sysreg(ttbr1, ttbr1_el1);
368 isb();
369 write_sysreg(ttbr0, ttbr0_el1);
370 isb();
371 post_ttbr_update_workaround();
372 }
373
asids_update_limit(void)374 static int asids_update_limit(void)
375 {
376 unsigned long num_available_asids = NUM_USER_ASIDS;
377
378 if (arm64_kernel_unmapped_at_el0()) {
379 num_available_asids /= 2;
380 if (pinned_asid_map)
381 set_kpti_asid_bits(pinned_asid_map);
382 }
383 /*
384 * Expect allocation after rollover to fail if we don't have at least
385 * one more ASID than CPUs. ASID #0 is reserved for init_mm.
386 */
387 WARN_ON(num_available_asids - 1 <= num_possible_cpus());
388 pr_info("ASID allocator initialised with %lu entries\n",
389 num_available_asids);
390
391 /*
392 * There must always be an ASID available after rollover. Ensure that,
393 * even if all CPUs have a reserved ASID and the maximum number of ASIDs
394 * are pinned, there still is at least one empty slot in the ASID map.
395 */
396 max_pinned_asids = num_available_asids - num_possible_cpus() - 2;
397 return 0;
398 }
399 arch_initcall(asids_update_limit);
400
asids_init(void)401 static int asids_init(void)
402 {
403 asid_bits = get_cpu_asid_bits();
404 atomic64_set(&asid_generation, ASID_FIRST_VERSION);
405 asid_map = kcalloc(BITS_TO_LONGS(NUM_USER_ASIDS), sizeof(*asid_map),
406 GFP_KERNEL);
407 if (!asid_map)
408 panic("Failed to allocate bitmap for %lu ASIDs\n",
409 NUM_USER_ASIDS);
410
411 pinned_asid_map = kcalloc(BITS_TO_LONGS(NUM_USER_ASIDS),
412 sizeof(*pinned_asid_map), GFP_KERNEL);
413 nr_pinned_asids = 0;
414
415 /*
416 * We cannot call set_reserved_asid_bits() here because CPU
417 * caps are not finalized yet, so it is safer to assume KPTI
418 * and reserve kernel ASID's from beginning.
419 */
420 if (IS_ENABLED(CONFIG_UNMAP_KERNEL_AT_EL0))
421 set_kpti_asid_bits(asid_map);
422 return 0;
423 }
424 early_initcall(asids_init);
425
