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1// SPDX-License-Identifier: GPL-2.0
2/*
3 * check TSC synchronization.
4 *
5 * Copyright (C) 2006, Red Hat, Inc., Ingo Molnar
6 *
7 * We check whether all boot CPUs have their TSC's synchronized,
8 * print a warning if not and turn off the TSC clock-source.
9 *
10 * The warp-check is point-to-point between two CPUs, the CPU
11 * initiating the bootup is the 'source CPU', the freshly booting
12 * CPU is the 'target CPU'.
13 *
14 * Only two CPUs may participate - they can enter in any order.
15 * ( The serial nature of the boot logic and the CPU hotplug lock
16 * protects against more than 2 CPUs entering this code. )
17 */
18#include <linux/topology.h>
19#include <linux/spinlock.h>
20#include <linux/kernel.h>
21#include <linux/smp.h>
22#include <linux/nmi.h>
23#include <asm/tsc.h>
24
25struct tsc_adjust {
26 s64 bootval;
27 s64 adjusted;
28 unsigned long nextcheck;
29 bool warned;
30};
31
32static DEFINE_PER_CPU(struct tsc_adjust, tsc_adjust);
33
34/*
35 * TSC's on different sockets may be reset asynchronously.
36 * This may cause the TSC ADJUST value on socket 0 to be NOT 0.
37 */
38bool __read_mostly tsc_async_resets;
39
40void mark_tsc_async_resets(char *reason)
41{
42 if (tsc_async_resets)
43 return;
44 tsc_async_resets = true;
45 pr_info("tsc: Marking TSC async resets true due to %s\n", reason);
46}
47
48void tsc_verify_tsc_adjust(bool resume)
49{
50 struct tsc_adjust *adj = this_cpu_ptr(&tsc_adjust);
51 s64 curval;
52
53 if (!boot_cpu_has(X86_FEATURE_TSC_ADJUST))
54 return;
55
56 /* Skip unnecessary error messages if TSC already unstable */
57 if (check_tsc_unstable())
58 return;
59
60 /* Rate limit the MSR check */
61 if (!resume && time_before(jiffies, adj->nextcheck))
62 return;
63
64 adj->nextcheck = jiffies + HZ;
65
66 rdmsrl(MSR_IA32_TSC_ADJUST, curval);
67 if (adj->adjusted == curval)
68 return;
69
70 /* Restore the original value */
71 wrmsrl(MSR_IA32_TSC_ADJUST, adj->adjusted);
72
73 if (!adj->warned || resume) {
74 pr_warn(FW_BUG "TSC ADJUST differs: CPU%u %lld --> %lld. Restoring\n",
75 smp_processor_id(), adj->adjusted, curval);
76 adj->warned = true;
77 }
78}
79
80static void tsc_sanitize_first_cpu(struct tsc_adjust *cur, s64 bootval,
81 unsigned int cpu, bool bootcpu)
82{
83 /*
84 * First online CPU in a package stores the boot value in the
85 * adjustment value. This value might change later via the sync
86 * mechanism. If that fails we still can yell about boot values not
87 * being consistent.
88 *
89 * On the boot cpu we just force set the ADJUST value to 0 if it's
90 * non zero. We don't do that on non boot cpus because physical
91 * hotplug should have set the ADJUST register to a value > 0 so
92 * the TSC is in sync with the already running cpus.
93 *
94 * Also don't force the ADJUST value to zero if that is a valid value
95 * for socket 0 as determined by the system arch. This is required
96 * when multiple sockets are reset asynchronously with each other
97 * and socket 0 may not have an TSC ADJUST value of 0.
98 */
99 if (bootcpu && bootval != 0) {
100 if (likely(!tsc_async_resets)) {
101 pr_warn(FW_BUG "TSC ADJUST: CPU%u: %lld force to 0\n",
102 cpu, bootval);
103 wrmsrl(MSR_IA32_TSC_ADJUST, 0);
104 bootval = 0;
105 } else {
106 pr_info("TSC ADJUST: CPU%u: %lld NOT forced to 0\n",
107 cpu, bootval);
108 }
109 }
110 cur->adjusted = bootval;
111}
112
113#ifndef CONFIG_SMP
114bool __init tsc_store_and_check_tsc_adjust(bool bootcpu)
115{
116 struct tsc_adjust *cur = this_cpu_ptr(&tsc_adjust);
117 s64 bootval;
118
119 if (!boot_cpu_has(X86_FEATURE_TSC_ADJUST))
120 return false;
121
122 /* Skip unnecessary error messages if TSC already unstable */
123 if (check_tsc_unstable())
124 return false;
125
126 rdmsrl(MSR_IA32_TSC_ADJUST, bootval);
127 cur->bootval = bootval;
128 cur->nextcheck = jiffies + HZ;
129 tsc_sanitize_first_cpu(cur, bootval, smp_processor_id(), bootcpu);
130 return false;
131}
132
133#else /* !CONFIG_SMP */
134
135/*
136 * Store and check the TSC ADJUST MSR if available
137 */
138bool tsc_store_and_check_tsc_adjust(bool bootcpu)
139{
140 struct tsc_adjust *ref, *cur = this_cpu_ptr(&tsc_adjust);
141 unsigned int refcpu, cpu = smp_processor_id();
142 struct cpumask *mask;
143 s64 bootval;
144
145 if (!boot_cpu_has(X86_FEATURE_TSC_ADJUST))
146 return false;
147
148 rdmsrl(MSR_IA32_TSC_ADJUST, bootval);
149 cur->bootval = bootval;
150 cur->nextcheck = jiffies + HZ;
151 cur->warned = false;
152
153 /*
154 * If a non-zero TSC value for socket 0 may be valid then the default
155 * adjusted value cannot assumed to be zero either.
156 */
157 if (tsc_async_resets)
158 cur->adjusted = bootval;
159
160 /*
161 * Check whether this CPU is the first in a package to come up. In
162 * this case do not check the boot value against another package
163 * because the new package might have been physically hotplugged,
164 * where TSC_ADJUST is expected to be different. When called on the
165 * boot CPU topology_core_cpumask() might not be available yet.
166 */
167 mask = topology_core_cpumask(cpu);
168 refcpu = mask ? cpumask_any_but(mask, cpu) : nr_cpu_ids;
169
170 if (refcpu >= nr_cpu_ids) {
171 tsc_sanitize_first_cpu(cur, bootval, smp_processor_id(),
172 bootcpu);
173 return false;
174 }
175
176 ref = per_cpu_ptr(&tsc_adjust, refcpu);
177 /*
178 * Compare the boot value and complain if it differs in the
179 * package.
180 */
181 if (bootval != ref->bootval)
182 printk_once(FW_BUG "TSC ADJUST differs within socket(s), fixing all errors\n");
183
184 /*
185 * The TSC_ADJUST values in a package must be the same. If the boot
186 * value on this newly upcoming CPU differs from the adjustment
187 * value of the already online CPU in this package, set it to that
188 * adjusted value.
189 */
190 if (bootval != ref->adjusted) {
191 cur->adjusted = ref->adjusted;
192 wrmsrl(MSR_IA32_TSC_ADJUST, ref->adjusted);
193 }
194 /*
195 * We have the TSCs forced to be in sync on this package. Skip sync
196 * test:
197 */
198 return true;
199}
200
201/*
202 * Entry/exit counters that make sure that both CPUs
203 * run the measurement code at once:
204 */
205static atomic_t start_count;
206static atomic_t stop_count;
207static atomic_t skip_test;
208static atomic_t test_runs;
209
210/*
211 * We use a raw spinlock in this exceptional case, because
212 * we want to have the fastest, inlined, non-debug version
213 * of a critical section, to be able to prove TSC time-warps:
214 */
215static arch_spinlock_t sync_lock = __ARCH_SPIN_LOCK_UNLOCKED;
216
217static cycles_t last_tsc;
218static cycles_t max_warp;
219static int nr_warps;
220static int random_warps;
221
222/*
223 * TSC-warp measurement loop running on both CPUs. This is not called
224 * if there is no TSC.
225 */
226static cycles_t check_tsc_warp(unsigned int timeout)
227{
228 cycles_t start, now, prev, end, cur_max_warp = 0;
229 int i, cur_warps = 0;
230
231 start = rdtsc_ordered();
232 /*
233 * The measurement runs for 'timeout' msecs:
234 */
235 end = start + (cycles_t) tsc_khz * timeout;
236 now = start;
237
238 for (i = 0; ; i++) {
239 /*
240 * We take the global lock, measure TSC, save the
241 * previous TSC that was measured (possibly on
242 * another CPU) and update the previous TSC timestamp.
243 */
244 arch_spin_lock(&sync_lock);
245 prev = last_tsc;
246 now = rdtsc_ordered();
247 last_tsc = now;
248 arch_spin_unlock(&sync_lock);
249
250 /*
251 * Be nice every now and then (and also check whether
252 * measurement is done [we also insert a 10 million
253 * loops safety exit, so we dont lock up in case the
254 * TSC readout is totally broken]):
255 */
256 if (unlikely(!(i & 7))) {
257 if (now > end || i > 10000000)
258 break;
259 cpu_relax();
260 touch_nmi_watchdog();
261 }
262 /*
263 * Outside the critical section we can now see whether
264 * we saw a time-warp of the TSC going backwards:
265 */
266 if (unlikely(prev > now)) {
267 arch_spin_lock(&sync_lock);
268 max_warp = max(max_warp, prev - now);
269 cur_max_warp = max_warp;
270 /*
271 * Check whether this bounces back and forth. Only
272 * one CPU should observe time going backwards.
273 */
274 if (cur_warps != nr_warps)
275 random_warps++;
276 nr_warps++;
277 cur_warps = nr_warps;
278 arch_spin_unlock(&sync_lock);
279 }
280 }
281 WARN(!(now-start),
282 "Warning: zero tsc calibration delta: %Ld [max: %Ld]\n",
283 now-start, end-start);
284 return cur_max_warp;
285}
286
287/*
288 * If the target CPU coming online doesn't have any of its core-siblings
289 * online, a timeout of 20msec will be used for the TSC-warp measurement
290 * loop. Otherwise a smaller timeout of 2msec will be used, as we have some
291 * information about this socket already (and this information grows as we
292 * have more and more logical-siblings in that socket).
293 *
294 * Ideally we should be able to skip the TSC sync check on the other
295 * core-siblings, if the first logical CPU in a socket passed the sync test.
296 * But as the TSC is per-logical CPU and can potentially be modified wrongly
297 * by the bios, TSC sync test for smaller duration should be able
298 * to catch such errors. Also this will catch the condition where all the
299 * cores in the socket doesn't get reset at the same time.
300 */
301static inline unsigned int loop_timeout(int cpu)
302{
303 return (cpumask_weight(topology_core_cpumask(cpu)) > 1) ? 2 : 20;
304}
305
306/*
307 * Source CPU calls into this - it waits for the freshly booted
308 * target CPU to arrive and then starts the measurement:
309 */
310void check_tsc_sync_source(int cpu)
311{
312 int cpus = 2;
313
314 /*
315 * No need to check if we already know that the TSC is not
316 * synchronized or if we have no TSC.
317 */
318 if (unsynchronized_tsc())
319 return;
320
321 /*
322 * Set the maximum number of test runs to
323 * 1 if the CPU does not provide the TSC_ADJUST MSR
324 * 3 if the MSR is available, so the target can try to adjust
325 */
326 if (!boot_cpu_has(X86_FEATURE_TSC_ADJUST))
327 atomic_set(&test_runs, 1);
328 else
329 atomic_set(&test_runs, 3);
330retry:
331 /*
332 * Wait for the target to start or to skip the test:
333 */
334 while (atomic_read(&start_count) != cpus - 1) {
335 if (atomic_read(&skip_test) > 0) {
336 atomic_set(&skip_test, 0);
337 return;
338 }
339 cpu_relax();
340 }
341
342 /*
343 * Trigger the target to continue into the measurement too:
344 */
345 atomic_inc(&start_count);
346
347 check_tsc_warp(loop_timeout(cpu));
348
349 while (atomic_read(&stop_count) != cpus-1)
350 cpu_relax();
351
352 /*
353 * If the test was successful set the number of runs to zero and
354 * stop. If not, decrement the number of runs an check if we can
355 * retry. In case of random warps no retry is attempted.
356 */
357 if (!nr_warps) {
358 atomic_set(&test_runs, 0);
359
360 pr_debug("TSC synchronization [CPU#%d -> CPU#%d]: passed\n",
361 smp_processor_id(), cpu);
362
363 } else if (atomic_dec_and_test(&test_runs) || random_warps) {
364 /* Force it to 0 if random warps brought us here */
365 atomic_set(&test_runs, 0);
366
367 pr_warning("TSC synchronization [CPU#%d -> CPU#%d]:\n",
368 smp_processor_id(), cpu);
369 pr_warning("Measured %Ld cycles TSC warp between CPUs, "
370 "turning off TSC clock.\n", max_warp);
371 if (random_warps)
372 pr_warning("TSC warped randomly between CPUs\n");
373 mark_tsc_unstable("check_tsc_sync_source failed");
374 }
375
376 /*
377 * Reset it - just in case we boot another CPU later:
378 */
379 atomic_set(&start_count, 0);
380 random_warps = 0;
381 nr_warps = 0;
382 max_warp = 0;
383 last_tsc = 0;
384
385 /*
386 * Let the target continue with the bootup:
387 */
388 atomic_inc(&stop_count);
389
390 /*
391 * Retry, if there is a chance to do so.
392 */
393 if (atomic_read(&test_runs) > 0)
394 goto retry;
395}
396
397/*
398 * Freshly booted CPUs call into this:
399 */
400void check_tsc_sync_target(void)
401{
402 struct tsc_adjust *cur = this_cpu_ptr(&tsc_adjust);
403 unsigned int cpu = smp_processor_id();
404 cycles_t cur_max_warp, gbl_max_warp;
405 int cpus = 2;
406
407 /* Also aborts if there is no TSC. */
408 if (unsynchronized_tsc())
409 return;
410
411 /*
412 * Store, verify and sanitize the TSC adjust register. If
413 * successful skip the test.
414 *
415 * The test is also skipped when the TSC is marked reliable. This
416 * is true for SoCs which have no fallback clocksource. On these
417 * SoCs the TSC is frequency synchronized, but still the TSC ADJUST
418 * register might have been wreckaged by the BIOS..
419 */
420 if (tsc_store_and_check_tsc_adjust(false) || tsc_clocksource_reliable) {
421 atomic_inc(&skip_test);
422 return;
423 }
424
425retry:
426 /*
427 * Register this CPU's participation and wait for the
428 * source CPU to start the measurement:
429 */
430 atomic_inc(&start_count);
431 while (atomic_read(&start_count) != cpus)
432 cpu_relax();
433
434 cur_max_warp = check_tsc_warp(loop_timeout(cpu));
435
436 /*
437 * Store the maximum observed warp value for a potential retry:
438 */
439 gbl_max_warp = max_warp;
440
441 /*
442 * Ok, we are done:
443 */
444 atomic_inc(&stop_count);
445
446 /*
447 * Wait for the source CPU to print stuff:
448 */
449 while (atomic_read(&stop_count) != cpus)
450 cpu_relax();
451
452 /*
453 * Reset it for the next sync test:
454 */
455 atomic_set(&stop_count, 0);
456
457 /*
458 * Check the number of remaining test runs. If not zero, the test
459 * failed and a retry with adjusted TSC is possible. If zero the
460 * test was either successful or failed terminally.
461 */
462 if (!atomic_read(&test_runs))
463 return;
464
465 /*
466 * If the warp value of this CPU is 0, then the other CPU
467 * observed time going backwards so this TSC was ahead and
468 * needs to move backwards.
469 */
470 if (!cur_max_warp)
471 cur_max_warp = -gbl_max_warp;
472
473 /*
474 * Add the result to the previous adjustment value.
475 *
476 * The adjustement value is slightly off by the overhead of the
477 * sync mechanism (observed values are ~200 TSC cycles), but this
478 * really depends on CPU, node distance and frequency. So
479 * compensating for this is hard to get right. Experiments show
480 * that the warp is not longer detectable when the observed warp
481 * value is used. In the worst case the adjustment needs to go
482 * through a 3rd run for fine tuning.
483 */
484 cur->adjusted += cur_max_warp;
485
486 pr_warn("TSC ADJUST compensate: CPU%u observed %lld warp. Adjust: %lld\n",
487 cpu, cur_max_warp, cur->adjusted);
488
489 wrmsrl(MSR_IA32_TSC_ADJUST, cur->adjusted);
490 goto retry;
491
492}
493
494#endif /* CONFIG_SMP */
1/*
2 * check TSC synchronization.
3 *
4 * Copyright (C) 2006, Red Hat, Inc., Ingo Molnar
5 *
6 * We check whether all boot CPUs have their TSC's synchronized,
7 * print a warning if not and turn off the TSC clock-source.
8 *
9 * The warp-check is point-to-point between two CPUs, the CPU
10 * initiating the bootup is the 'source CPU', the freshly booting
11 * CPU is the 'target CPU'.
12 *
13 * Only two CPUs may participate - they can enter in any order.
14 * ( The serial nature of the boot logic and the CPU hotplug lock
15 * protects against more than 2 CPUs entering this code. )
16 */
17#include <linux/spinlock.h>
18#include <linux/kernel.h>
19#include <linux/smp.h>
20#include <linux/nmi.h>
21#include <asm/tsc.h>
22
23/*
24 * Entry/exit counters that make sure that both CPUs
25 * run the measurement code at once:
26 */
27static atomic_t start_count;
28static atomic_t stop_count;
29
30/*
31 * We use a raw spinlock in this exceptional case, because
32 * we want to have the fastest, inlined, non-debug version
33 * of a critical section, to be able to prove TSC time-warps:
34 */
35static arch_spinlock_t sync_lock = __ARCH_SPIN_LOCK_UNLOCKED;
36
37static cycles_t last_tsc;
38static cycles_t max_warp;
39static int nr_warps;
40
41/*
42 * TSC-warp measurement loop running on both CPUs. This is not called
43 * if there is no TSC.
44 */
45static void check_tsc_warp(unsigned int timeout)
46{
47 cycles_t start, now, prev, end;
48 int i;
49
50 start = rdtsc_ordered();
51 /*
52 * The measurement runs for 'timeout' msecs:
53 */
54 end = start + (cycles_t) tsc_khz * timeout;
55 now = start;
56
57 for (i = 0; ; i++) {
58 /*
59 * We take the global lock, measure TSC, save the
60 * previous TSC that was measured (possibly on
61 * another CPU) and update the previous TSC timestamp.
62 */
63 arch_spin_lock(&sync_lock);
64 prev = last_tsc;
65 now = rdtsc_ordered();
66 last_tsc = now;
67 arch_spin_unlock(&sync_lock);
68
69 /*
70 * Be nice every now and then (and also check whether
71 * measurement is done [we also insert a 10 million
72 * loops safety exit, so we dont lock up in case the
73 * TSC readout is totally broken]):
74 */
75 if (unlikely(!(i & 7))) {
76 if (now > end || i > 10000000)
77 break;
78 cpu_relax();
79 touch_nmi_watchdog();
80 }
81 /*
82 * Outside the critical section we can now see whether
83 * we saw a time-warp of the TSC going backwards:
84 */
85 if (unlikely(prev > now)) {
86 arch_spin_lock(&sync_lock);
87 max_warp = max(max_warp, prev - now);
88 nr_warps++;
89 arch_spin_unlock(&sync_lock);
90 }
91 }
92 WARN(!(now-start),
93 "Warning: zero tsc calibration delta: %Ld [max: %Ld]\n",
94 now-start, end-start);
95}
96
97/*
98 * If the target CPU coming online doesn't have any of its core-siblings
99 * online, a timeout of 20msec will be used for the TSC-warp measurement
100 * loop. Otherwise a smaller timeout of 2msec will be used, as we have some
101 * information about this socket already (and this information grows as we
102 * have more and more logical-siblings in that socket).
103 *
104 * Ideally we should be able to skip the TSC sync check on the other
105 * core-siblings, if the first logical CPU in a socket passed the sync test.
106 * But as the TSC is per-logical CPU and can potentially be modified wrongly
107 * by the bios, TSC sync test for smaller duration should be able
108 * to catch such errors. Also this will catch the condition where all the
109 * cores in the socket doesn't get reset at the same time.
110 */
111static inline unsigned int loop_timeout(int cpu)
112{
113 return (cpumask_weight(topology_core_cpumask(cpu)) > 1) ? 2 : 20;
114}
115
116/*
117 * Source CPU calls into this - it waits for the freshly booted
118 * target CPU to arrive and then starts the measurement:
119 */
120void check_tsc_sync_source(int cpu)
121{
122 int cpus = 2;
123
124 /*
125 * No need to check if we already know that the TSC is not
126 * synchronized or if we have no TSC.
127 */
128 if (unsynchronized_tsc())
129 return;
130
131 if (tsc_clocksource_reliable) {
132 if (cpu == (nr_cpu_ids-1) || system_state != SYSTEM_BOOTING)
133 pr_info(
134 "Skipped synchronization checks as TSC is reliable.\n");
135 return;
136 }
137
138 /*
139 * Reset it - in case this is a second bootup:
140 */
141 atomic_set(&stop_count, 0);
142
143 /*
144 * Wait for the target to arrive:
145 */
146 while (atomic_read(&start_count) != cpus-1)
147 cpu_relax();
148 /*
149 * Trigger the target to continue into the measurement too:
150 */
151 atomic_inc(&start_count);
152
153 check_tsc_warp(loop_timeout(cpu));
154
155 while (atomic_read(&stop_count) != cpus-1)
156 cpu_relax();
157
158 if (nr_warps) {
159 pr_warning("TSC synchronization [CPU#%d -> CPU#%d]:\n",
160 smp_processor_id(), cpu);
161 pr_warning("Measured %Ld cycles TSC warp between CPUs, "
162 "turning off TSC clock.\n", max_warp);
163 mark_tsc_unstable("check_tsc_sync_source failed");
164 } else {
165 pr_debug("TSC synchronization [CPU#%d -> CPU#%d]: passed\n",
166 smp_processor_id(), cpu);
167 }
168
169 /*
170 * Reset it - just in case we boot another CPU later:
171 */
172 atomic_set(&start_count, 0);
173 nr_warps = 0;
174 max_warp = 0;
175 last_tsc = 0;
176
177 /*
178 * Let the target continue with the bootup:
179 */
180 atomic_inc(&stop_count);
181}
182
183/*
184 * Freshly booted CPUs call into this:
185 */
186void check_tsc_sync_target(void)
187{
188 int cpus = 2;
189
190 /* Also aborts if there is no TSC. */
191 if (unsynchronized_tsc() || tsc_clocksource_reliable)
192 return;
193
194 /*
195 * Register this CPU's participation and wait for the
196 * source CPU to start the measurement:
197 */
198 atomic_inc(&start_count);
199 while (atomic_read(&start_count) != cpus)
200 cpu_relax();
201
202 check_tsc_warp(loop_timeout(smp_processor_id()));
203
204 /*
205 * Ok, we are done:
206 */
207 atomic_inc(&stop_count);
208
209 /*
210 * Wait for the source CPU to print stuff:
211 */
212 while (atomic_read(&stop_count) != cpus)
213 cpu_relax();
214}