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