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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 : :
25 : : struct tsc_adjust {
26 : : s64 bootval;
27 : : s64 adjusted;
28 : : unsigned long nextcheck;
29 : : bool warned;
30 : : };
31 : :
32 : : static 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 : : */
38 : : bool __read_mostly tsc_async_resets;
39 : :
40 : 0 : void mark_tsc_async_resets(char *reason)
41 : : {
42 [ # # ]: 0 : if (tsc_async_resets)
43 : : return;
44 : 0 : tsc_async_resets = true;
45 : 0 : pr_info("tsc: Marking TSC async resets true due to %s\n", reason);
46 : : }
47 : :
48 : 11012 : void tsc_verify_tsc_adjust(bool resume)
49 : : {
50 : 11012 : struct tsc_adjust *adj = this_cpu_ptr(&tsc_adjust);
51 : 11012 : s64 curval;
52 : :
53 [ - + ]: 11012 : if (!boot_cpu_has(X86_FEATURE_TSC_ADJUST))
54 : : return;
55 : :
56 : : /* Skip unnecessary error messages if TSC already unstable */
57 [ # # ]: 0 : if (check_tsc_unstable())
58 : : return;
59 : :
60 : : /* Rate limit the MSR check */
61 [ # # # # ]: 0 : if (!resume && time_before(jiffies, adj->nextcheck))
62 : : return;
63 : :
64 : 0 : adj->nextcheck = jiffies + HZ;
65 : :
66 : 0 : rdmsrl(MSR_IA32_TSC_ADJUST, curval);
67 [ # # ]: 0 : if (adj->adjusted == curval)
68 : : return;
69 : :
70 : : /* Restore the original value */
71 : 0 : wrmsrl(MSR_IA32_TSC_ADJUST, adj->adjusted);
72 : :
73 [ # # # # ]: 0 : if (!adj->warned || resume) {
74 : 0 : pr_warn(FW_BUG "TSC ADJUST differs: CPU%u %lld --> %lld. Restoring\n",
75 : : smp_processor_id(), adj->adjusted, curval);
76 : 0 : adj->warned = true;
77 : : }
78 : : }
79 : :
80 : 0 : static 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 [ # # ]: 0 : if (bootcpu && bootval != 0) {
100 [ # # ]: 0 : if (likely(!tsc_async_resets)) {
101 : 0 : pr_warn(FW_BUG "TSC ADJUST: CPU%u: %lld force to 0\n",
102 : : cpu, bootval);
103 : 0 : wrmsrl(MSR_IA32_TSC_ADJUST, 0);
104 : 0 : bootval = 0;
105 : : } else {
106 : 0 : pr_info("TSC ADJUST: CPU%u: %lld NOT forced to 0\n",
107 : : cpu, bootval);
108 : : }
109 : : }
110 : 0 : cur->adjusted = bootval;
111 : 0 : }
112 : :
113 : : #ifndef CONFIG_SMP
114 : : bool __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 : : */
138 : 28 : bool tsc_store_and_check_tsc_adjust(bool bootcpu)
139 : : {
140 : 28 : struct tsc_adjust *ref, *cur = this_cpu_ptr(&tsc_adjust);
141 : 28 : unsigned int refcpu, cpu = smp_processor_id();
142 : 28 : struct cpumask *mask;
143 : 28 : s64 bootval;
144 : :
145 [ - + ]: 28 : if (!boot_cpu_has(X86_FEATURE_TSC_ADJUST))
146 : : return false;
147 : :
148 : 0 : rdmsrl(MSR_IA32_TSC_ADJUST, bootval);
149 : 0 : cur->bootval = bootval;
150 : 0 : cur->nextcheck = jiffies + HZ;
151 : 0 : 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 [ # # ]: 0 : if (tsc_async_resets)
158 : 0 : 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 : 0 : mask = topology_core_cpumask(cpu);
168 [ # # ]: 0 : refcpu = mask ? cpumask_any_but(mask, cpu) : nr_cpu_ids;
169 : :
170 [ # # ]: 0 : if (refcpu >= nr_cpu_ids) {
171 : 0 : tsc_sanitize_first_cpu(cur, bootval, smp_processor_id(),
172 : : bootcpu);
173 : 0 : return false;
174 : : }
175 : :
176 : 0 : ref = per_cpu_ptr(&tsc_adjust, refcpu);
177 : : /*
178 : : * Compare the boot value and complain if it differs in the
179 : : * package.
180 : : */
181 [ # # ]: 0 : if (bootval != ref->bootval)
182 [ # # ]: 0 : 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 [ # # ]: 0 : if (bootval != ref->adjusted) {
191 : 0 : cur->adjusted = ref->adjusted;
192 : 0 : 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 : : */
205 : : static atomic_t start_count;
206 : : static atomic_t stop_count;
207 : : static atomic_t skip_test;
208 : : static 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 : : */
215 : : static arch_spinlock_t sync_lock = __ARCH_SPIN_LOCK_UNLOCKED;
216 : :
217 : : static cycles_t last_tsc;
218 : : static cycles_t max_warp;
219 : : static int nr_warps;
220 : : static 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 : : */
226 : 0 : static cycles_t check_tsc_warp(unsigned int timeout)
227 : : {
228 : 0 : cycles_t start, now, prev, end, cur_max_warp = 0;
229 : 0 : int i, cur_warps = 0;
230 : :
231 : 0 : start = rdtsc_ordered();
232 : : /*
233 : : * The measurement runs for 'timeout' msecs:
234 : : */
235 : 0 : end = start + (cycles_t) tsc_khz * timeout;
236 : :
237 : 0 : for (i = 0; ; i++) {
238 : : /*
239 : : * We take the global lock, measure TSC, save the
240 : : * previous TSC that was measured (possibly on
241 : : * another CPU) and update the previous TSC timestamp.
242 : : */
243 : 0 : arch_spin_lock(&sync_lock);
244 : 0 : prev = last_tsc;
245 : 0 : now = rdtsc_ordered();
246 : 0 : last_tsc = now;
247 : 0 : arch_spin_unlock(&sync_lock);
248 : :
249 : : /*
250 : : * Be nice every now and then (and also check whether
251 : : * measurement is done [we also insert a 10 million
252 : : * loops safety exit, so we dont lock up in case the
253 : : * TSC readout is totally broken]):
254 : : */
255 [ # # ]: 0 : if (unlikely(!(i & 7))) {
256 [ # # ]: 0 : if (now > end || i > 10000000)
257 : : break;
258 : 0 : cpu_relax();
259 : 0 : touch_nmi_watchdog();
260 : : }
261 : : /*
262 : : * Outside the critical section we can now see whether
263 : : * we saw a time-warp of the TSC going backwards:
264 : : */
265 [ # # ]: 0 : if (unlikely(prev > now)) {
266 : 0 : arch_spin_lock(&sync_lock);
267 : 0 : max_warp = max(max_warp, prev - now);
268 : 0 : cur_max_warp = max_warp;
269 : : /*
270 : : * Check whether this bounces back and forth. Only
271 : : * one CPU should observe time going backwards.
272 : : */
273 [ # # ]: 0 : if (cur_warps != nr_warps)
274 : 0 : random_warps++;
275 : 0 : nr_warps++;
276 : 0 : cur_warps = nr_warps;
277 : 0 : arch_spin_unlock(&sync_lock);
278 : : }
279 : : }
280 [ # # ]: 0 : WARN(!(now-start),
281 : : "Warning: zero tsc calibration delta: %Ld [max: %Ld]\n",
282 : : now-start, end-start);
283 : 0 : return cur_max_warp;
284 : : }
285 : :
286 : : /*
287 : : * If the target CPU coming online doesn't have any of its core-siblings
288 : : * online, a timeout of 20msec will be used for the TSC-warp measurement
289 : : * loop. Otherwise a smaller timeout of 2msec will be used, as we have some
290 : : * information about this socket already (and this information grows as we
291 : : * have more and more logical-siblings in that socket).
292 : : *
293 : : * Ideally we should be able to skip the TSC sync check on the other
294 : : * core-siblings, if the first logical CPU in a socket passed the sync test.
295 : : * But as the TSC is per-logical CPU and can potentially be modified wrongly
296 : : * by the bios, TSC sync test for smaller duration should be able
297 : : * to catch such errors. Also this will catch the condition where all the
298 : : * cores in the socket doesn't get reset at the same time.
299 : : */
300 : 0 : static inline unsigned int loop_timeout(int cpu)
301 : : {
302 : 0 : return (cpumask_weight(topology_core_cpumask(cpu)) > 1) ? 2 : 20;
303 : : }
304 : :
305 : : /*
306 : : * Source CPU calls into this - it waits for the freshly booted
307 : : * target CPU to arrive and then starts the measurement:
308 : : */
309 : 0 : void check_tsc_sync_source(int cpu)
310 : : {
311 : 0 : int cpus = 2;
312 : :
313 : : /*
314 : : * No need to check if we already know that the TSC is not
315 : : * synchronized or if we have no TSC.
316 : : */
317 [ # # ]: 0 : if (unsynchronized_tsc())
318 : : return;
319 : :
320 : : /*
321 : : * Set the maximum number of test runs to
322 : : * 1 if the CPU does not provide the TSC_ADJUST MSR
323 : : * 3 if the MSR is available, so the target can try to adjust
324 : : */
325 [ # # ]: 0 : if (!boot_cpu_has(X86_FEATURE_TSC_ADJUST))
326 : 0 : atomic_set(&test_runs, 1);
327 : : else
328 : 0 : atomic_set(&test_runs, 3);
329 : : retry:
330 : : /*
331 : : * Wait for the target to start or to skip the test:
332 : : */
333 [ # # ]: 0 : while (atomic_read(&start_count) != cpus - 1) {
334 [ # # ]: 0 : if (atomic_read(&skip_test) > 0) {
335 : 0 : atomic_set(&skip_test, 0);
336 : 0 : return;
337 : : }
338 : 0 : cpu_relax();
339 : : }
340 : :
341 : : /*
342 : : * Trigger the target to continue into the measurement too:
343 : : */
344 : 0 : atomic_inc(&start_count);
345 : :
346 [ # # ]: 0 : check_tsc_warp(loop_timeout(cpu));
347 : :
348 [ # # ]: 0 : while (atomic_read(&stop_count) != cpus-1)
349 : 0 : cpu_relax();
350 : :
351 : : /*
352 : : * If the test was successful set the number of runs to zero and
353 : : * stop. If not, decrement the number of runs an check if we can
354 : : * retry. In case of random warps no retry is attempted.
355 : : */
356 [ # # ]: 0 : if (!nr_warps) {
357 : 0 : atomic_set(&test_runs, 0);
358 : :
359 : 0 : pr_debug("TSC synchronization [CPU#%d -> CPU#%d]: passed\n",
360 : : smp_processor_id(), cpu);
361 : :
362 [ # # # # ]: 0 : } else if (atomic_dec_and_test(&test_runs) || random_warps) {
363 : : /* Force it to 0 if random warps brought us here */
364 : 0 : atomic_set(&test_runs, 0);
365 : :
366 : 0 : pr_warn("TSC synchronization [CPU#%d -> CPU#%d]:\n",
367 : : smp_processor_id(), cpu);
368 : 0 : pr_warn("Measured %Ld cycles TSC warp between CPUs, "
369 : : "turning off TSC clock.\n", max_warp);
370 [ # # ]: 0 : if (random_warps)
371 : 0 : pr_warn("TSC warped randomly between CPUs\n");
372 : 0 : mark_tsc_unstable("check_tsc_sync_source failed");
373 : : }
374 : :
375 : : /*
376 : : * Reset it - just in case we boot another CPU later:
377 : : */
378 : 0 : atomic_set(&start_count, 0);
379 : 0 : random_warps = 0;
380 : 0 : nr_warps = 0;
381 : 0 : max_warp = 0;
382 : 0 : last_tsc = 0;
383 : :
384 : : /*
385 : : * Let the target continue with the bootup:
386 : : */
387 : 0 : atomic_inc(&stop_count);
388 : :
389 : : /*
390 : : * Retry, if there is a chance to do so.
391 : : */
392 [ # # ]: 0 : if (atomic_read(&test_runs) > 0)
393 : 0 : goto retry;
394 : : }
395 : :
396 : : /*
397 : : * Freshly booted CPUs call into this:
398 : : */
399 : 0 : void check_tsc_sync_target(void)
400 : : {
401 : 0 : struct tsc_adjust *cur = this_cpu_ptr(&tsc_adjust);
402 : 0 : unsigned int cpu = smp_processor_id();
403 : 0 : cycles_t cur_max_warp, gbl_max_warp;
404 : 0 : int cpus = 2;
405 : :
406 : : /* Also aborts if there is no TSC. */
407 [ # # ]: 0 : if (unsynchronized_tsc())
408 : : return;
409 : :
410 : : /*
411 : : * Store, verify and sanitize the TSC adjust register. If
412 : : * successful skip the test.
413 : : *
414 : : * The test is also skipped when the TSC is marked reliable. This
415 : : * is true for SoCs which have no fallback clocksource. On these
416 : : * SoCs the TSC is frequency synchronized, but still the TSC ADJUST
417 : : * register might have been wreckaged by the BIOS..
418 : : */
419 [ # # # # ]: 0 : if (tsc_store_and_check_tsc_adjust(false) || tsc_clocksource_reliable) {
420 : 0 : atomic_inc(&skip_test);
421 : 0 : return;
422 : : }
423 : :
424 : 0 : retry:
425 : : /*
426 : : * Register this CPU's participation and wait for the
427 : : * source CPU to start the measurement:
428 : : */
429 : 0 : atomic_inc(&start_count);
430 [ # # ]: 0 : while (atomic_read(&start_count) != cpus)
431 : 0 : cpu_relax();
432 : :
433 [ # # ]: 0 : cur_max_warp = check_tsc_warp(loop_timeout(cpu));
434 : :
435 : : /*
436 : : * Store the maximum observed warp value for a potential retry:
437 : : */
438 : 0 : gbl_max_warp = max_warp;
439 : :
440 : : /*
441 : : * Ok, we are done:
442 : : */
443 : 0 : atomic_inc(&stop_count);
444 : :
445 : : /*
446 : : * Wait for the source CPU to print stuff:
447 : : */
448 [ # # ]: 0 : while (atomic_read(&stop_count) != cpus)
449 : 0 : cpu_relax();
450 : :
451 : : /*
452 : : * Reset it for the next sync test:
453 : : */
454 : 0 : atomic_set(&stop_count, 0);
455 : :
456 : : /*
457 : : * Check the number of remaining test runs. If not zero, the test
458 : : * failed and a retry with adjusted TSC is possible. If zero the
459 : : * test was either successful or failed terminally.
460 : : */
461 [ # # ]: 0 : if (!atomic_read(&test_runs))
462 : : return;
463 : :
464 : : /*
465 : : * If the warp value of this CPU is 0, then the other CPU
466 : : * observed time going backwards so this TSC was ahead and
467 : : * needs to move backwards.
468 : : */
469 [ # # ]: 0 : if (!cur_max_warp)
470 : 0 : cur_max_warp = -gbl_max_warp;
471 : :
472 : : /*
473 : : * Add the result to the previous adjustment value.
474 : : *
475 : : * The adjustement value is slightly off by the overhead of the
476 : : * sync mechanism (observed values are ~200 TSC cycles), but this
477 : : * really depends on CPU, node distance and frequency. So
478 : : * compensating for this is hard to get right. Experiments show
479 : : * that the warp is not longer detectable when the observed warp
480 : : * value is used. In the worst case the adjustment needs to go
481 : : * through a 3rd run for fine tuning.
482 : : */
483 : 0 : cur->adjusted += cur_max_warp;
484 : :
485 : 0 : pr_warn("TSC ADJUST compensate: CPU%u observed %lld warp. Adjust: %lld\n",
486 : : cpu, cur_max_warp, cur->adjusted);
487 : :
488 : 0 : wrmsrl(MSR_IA32_TSC_ADJUST, cur->adjusted);
489 : 0 : goto retry;
490 : :
491 : : }
492 : :
493 : : #endif /* CONFIG_SMP */
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