gettimeofday.h

  1/* SPDX-License-Identifier: GPL-2.0 */
  2/*
  3 * Fast user context implementation of clock_gettime, gettimeofday, and time.
  4 *
  5 * Copyright (C) 2019 ARM Limited.
  6 * Copyright 2006 Andi Kleen, SUSE Labs.
  7 * 32 Bit compat layer by Stefani Seibold <stefani@seibold.net>
  8 *  sponsored by Rohde & Schwarz GmbH & Co. KG Munich/Germany
  9 */
 10#ifndef __ASM_VDSO_GETTIMEOFDAY_H
 11#define __ASM_VDSO_GETTIMEOFDAY_H
 12
 13#ifndef __ASSEMBLER__
 14
 15#include <uapi/linux/time.h>
 16#include <asm/vgtod.h>
 17#include <asm/unistd.h>
 18#include <asm/msr.h>
 19#include <asm/pvclock.h>
 20#include <clocksource/hyperv_timer.h>
 21
 22#define VDSO_HAS_TIME 1
 23
 24#define VDSO_HAS_CLOCK_GETRES 1
 25
 26/*
 27 * Declare the memory-mapped vclock data pages.  These come from hypervisors.
 28 * If we ever reintroduce something like direct access to an MMIO clock like
 29 * the HPET again, it will go here as well.
 30 *
 31 * A load from any of these pages will segfault if the clock in question is
 32 * disabled, so appropriate compiler barriers and checks need to be used
 33 * to prevent stray loads.
 34 *
 35 * These declarations MUST NOT be const.  The compiler will assume that
 36 * an extern const variable has genuinely constant contents, and the
 37 * resulting code won't work, since the whole point is that these pages
 38 * change over time, possibly while we're accessing them.
 39 */
 40
 41#ifdef CONFIG_PARAVIRT_CLOCK
 42/*
 43 * This is the vCPU 0 pvclock page.  We only use pvclock from the vDSO
 44 * if the hypervisor tells us that all vCPUs can get valid data from the
 45 * vCPU 0 page.
 46 */
 47extern struct pvclock_vsyscall_time_info pvclock_page
 48	__attribute__((visibility("hidden")));
 49#endif
 50
 51#ifdef CONFIG_HYPERV_TIMER
 52extern struct ms_hyperv_tsc_page hvclock_page
 53	__attribute__((visibility("hidden")));
 54#endif
 55
 56#ifndef BUILD_VDSO32
 57
 58static __always_inline
 59long clock_gettime_fallback(clockid_t _clkid, struct __kernel_timespec *_ts)
 60{
 61	long ret;
 62
 63	asm ("syscall" : "=a" (ret), "=m" (*_ts) :
 64	     "0" (__NR_clock_gettime), "D" (_clkid), "S" (_ts) :
 65	     "rcx", "r11");
 66
 67	return ret;
 68}
 69
 70static __always_inline
 71long gettimeofday_fallback(struct __kernel_old_timeval *_tv,
 72			   struct timezone *_tz)
 73{
 74	long ret;
 75
 76	asm("syscall" : "=a" (ret) :
 77	    "0" (__NR_gettimeofday), "D" (_tv), "S" (_tz) : "memory");
 78
 79	return ret;
 80}
 81
 82static __always_inline
 83long clock_getres_fallback(clockid_t _clkid, struct __kernel_timespec *_ts)
 84{
 85	long ret;
 86
 87	asm ("syscall" : "=a" (ret), "=m" (*_ts) :
 88	     "0" (__NR_clock_getres), "D" (_clkid), "S" (_ts) :
 89	     "rcx", "r11");
 90
 91	return ret;
 92}
 93
 94#else
 95
 96static __always_inline
 97long clock_gettime_fallback(clockid_t _clkid, struct __kernel_timespec *_ts)
 98{
 99	long ret;
100
101	asm (
102		"mov %%ebx, %%edx \n"
103		"mov %[clock], %%ebx \n"
104		"call __kernel_vsyscall \n"
105		"mov %%edx, %%ebx \n"
106		: "=a" (ret), "=m" (*_ts)
107		: "0" (__NR_clock_gettime64), [clock] "g" (_clkid), "c" (_ts)
108		: "edx");
109
110	return ret;
111}
112
113static __always_inline
114long clock_gettime32_fallback(clockid_t _clkid, struct old_timespec32 *_ts)
115{
116	long ret;
117
118	asm (
119		"mov %%ebx, %%edx \n"
120		"mov %[clock], %%ebx \n"
121		"call __kernel_vsyscall \n"
122		"mov %%edx, %%ebx \n"
123		: "=a" (ret), "=m" (*_ts)
124		: "0" (__NR_clock_gettime), [clock] "g" (_clkid), "c" (_ts)
125		: "edx");
126
127	return ret;
128}
129
130static __always_inline
131long gettimeofday_fallback(struct __kernel_old_timeval *_tv,
132			   struct timezone *_tz)
133{
134	long ret;
135
136	asm(
137		"mov %%ebx, %%edx \n"
138		"mov %2, %%ebx \n"
139		"call __kernel_vsyscall \n"
140		"mov %%edx, %%ebx \n"
141		: "=a" (ret)
142		: "0" (__NR_gettimeofday), "g" (_tv), "c" (_tz)
143		: "memory", "edx");
144
145	return ret;
146}
147
148static __always_inline long
149clock_getres_fallback(clockid_t _clkid, struct __kernel_timespec *_ts)
150{
151	long ret;
152
153	asm (
154		"mov %%ebx, %%edx \n"
155		"mov %[clock], %%ebx \n"
156		"call __kernel_vsyscall \n"
157		"mov %%edx, %%ebx \n"
158		: "=a" (ret), "=m" (*_ts)
159		: "0" (__NR_clock_getres_time64), [clock] "g" (_clkid), "c" (_ts)
160		: "edx");
161
162	return ret;
163}
164
165static __always_inline
166long clock_getres32_fallback(clockid_t _clkid, struct old_timespec32 *_ts)
167{
168	long ret;
169
170	asm (
171		"mov %%ebx, %%edx \n"
172		"mov %[clock], %%ebx \n"
173		"call __kernel_vsyscall \n"
174		"mov %%edx, %%ebx \n"
175		: "=a" (ret), "=m" (*_ts)
176		: "0" (__NR_clock_getres), [clock] "g" (_clkid), "c" (_ts)
177		: "edx");
178
179	return ret;
180}
181
182#endif
183
184#ifdef CONFIG_PARAVIRT_CLOCK
185static u64 vread_pvclock(void)
186{
187	const struct pvclock_vcpu_time_info *pvti = &pvclock_page.pvti;
188	u32 version;
189	u64 ret;
190
191	/*
192	 * Note: The kernel and hypervisor must guarantee that cpu ID
193	 * number maps 1:1 to per-CPU pvclock time info.
194	 *
195	 * Because the hypervisor is entirely unaware of guest userspace
196	 * preemption, it cannot guarantee that per-CPU pvclock time
197	 * info is updated if the underlying CPU changes or that that
198	 * version is increased whenever underlying CPU changes.
199	 *
200	 * On KVM, we are guaranteed that pvti updates for any vCPU are
201	 * atomic as seen by *all* vCPUs.  This is an even stronger
202	 * guarantee than we get with a normal seqlock.
203	 *
204	 * On Xen, we don't appear to have that guarantee, but Xen still
205	 * supplies a valid seqlock using the version field.
206	 *
207	 * We only do pvclock vdso timing at all if
208	 * PVCLOCK_TSC_STABLE_BIT is set, and we interpret that bit to
209	 * mean that all vCPUs have matching pvti and that the TSC is
210	 * synced, so we can just look at vCPU 0's pvti.
211	 */
212
213	do {
214		version = pvclock_read_begin(pvti);
215
216		if (unlikely(!(pvti->flags & PVCLOCK_TSC_STABLE_BIT)))
217			return U64_MAX;
218
219		ret = __pvclock_read_cycles(pvti, rdtsc_ordered());
220	} while (pvclock_read_retry(pvti, version));
221
222	return ret & S64_MAX;
223}
224#endif
225
226#ifdef CONFIG_HYPERV_TIMER
227static u64 vread_hvclock(void)
228{
229	u64 tsc, time;
230
231	if (hv_read_tsc_page_tsc(&hvclock_page, &tsc, &time))
232		return time & S64_MAX;
233
234	return U64_MAX;
235}
236#endif
237
238static inline u64 __arch_get_hw_counter(s32 clock_mode,
239					const struct vdso_time_data *vd)
240{
241	if (likely(clock_mode == VDSO_CLOCKMODE_TSC))
242		return (u64)rdtsc_ordered() & S64_MAX;
243	/*
244	 * For any memory-mapped vclock type, we need to make sure that gcc
245	 * doesn't cleverly hoist a load before the mode check.  Otherwise we
246	 * might end up touching the memory-mapped page even if the vclock in
247	 * question isn't enabled, which will segfault.  Hence the barriers.
248	 */
249#ifdef CONFIG_PARAVIRT_CLOCK
250	if (clock_mode == VDSO_CLOCKMODE_PVCLOCK) {
251		barrier();
252		return vread_pvclock();
253	}
254#endif
255#ifdef CONFIG_HYPERV_TIMER
256	if (clock_mode == VDSO_CLOCKMODE_HVCLOCK) {
257		barrier();
258		return vread_hvclock();
259	}
260#endif
261	return U64_MAX;
262}
263
264static inline bool arch_vdso_clocksource_ok(const struct vdso_clock *vc)
265{
266	return true;
267}
268#define vdso_clocksource_ok arch_vdso_clocksource_ok
269
270/*
271 * Clocksource read value validation to handle PV and HyperV clocksources
272 * which can be invalidated asynchronously and indicate invalidation by
273 * returning U64_MAX, which can be effectively tested by checking for a
274 * negative value after casting it to s64.
275 *
276 * This effectively forces a S64_MAX mask on the calculations, unlike the
277 * U64_MAX mask normally used by x86 clocksources.
278 */
279static inline bool arch_vdso_cycles_ok(u64 cycles)
280{
281	return (s64)cycles >= 0;
282}
283#define vdso_cycles_ok arch_vdso_cycles_ok
284
285/*
286 * x86 specific calculation of nanoseconds for the current cycle count
287 *
288 * The regular implementation assumes that clocksource reads are globally
289 * monotonic. The TSC can be slightly off across sockets which can cause
290 * the regular delta calculation (@cycles - @last) to return a huge time
291 * jump.
292 *
293 * Therefore it needs to be verified that @cycles are greater than
294 * @vd->cycles_last. If not then use @vd->cycles_last, which is the base
295 * time of the current conversion period.
296 *
297 * This variant also uses a custom mask because while the clocksource mask of
298 * all the VDSO capable clocksources on x86 is U64_MAX, the above code uses
299 * U64_MASK as an exception value, additionally arch_vdso_cycles_ok() above
300 * declares everything with the MSB/Sign-bit set as invalid. Therefore the
301 * effective mask is S64_MAX.
302 */
303static __always_inline u64 vdso_calc_ns(const struct vdso_clock *vc, u64 cycles, u64 base)
304{
305	u64 delta = cycles - vc->cycle_last;
306
307	/*
308	 * Negative motion and deltas which can cause multiplication
309	 * overflow require special treatment. This check covers both as
310	 * negative motion is guaranteed to be greater than @vc::max_cycles
311	 * due to unsigned comparison.
312	 *
313	 * Due to the MSB/Sign-bit being used as invalid marker (see
314	 * arch_vdso_cycles_ok() above), the effective mask is S64_MAX, but that
315	 * case is also unlikely and will also take the unlikely path here.
316	 */
317	if (unlikely(delta > vc->max_cycles)) {
318		/*
319		 * Due to the above mentioned TSC wobbles, filter out
320		 * negative motion.  Per the above masking, the effective
321		 * sign bit is now bit 62.
322		 */
323		if (delta & (1ULL << 62))
324			return base >> vc->shift;
325
326		/* Handle multiplication overflow gracefully */
327		return mul_u64_u32_add_u64_shr(delta & S64_MAX, vc->mult, base, vc->shift);
328	}
329
330	return ((delta * vc->mult) + base) >> vc->shift;
331}
332#define vdso_calc_ns vdso_calc_ns
333
334#endif /* !__ASSEMBLER__ */
335
336#endif /* __ASM_VDSO_GETTIMEOFDAY_H */