1 /*
2  * Copyright 2006 Andi Kleen, SUSE Labs.
3  * Subject to the GNU Public License, v.2
4  *
5  * Fast user context implementation of clock_gettime, gettimeofday, and time.
6  *
7  * 32 Bit compat layer by Stefani Seibold <stefani@seibold.net>
8  *  sponsored by Rohde & Schwarz GmbH & Co. KG Munich/Germany
9  *
10  * The code should have no internal unresolved relocations.
11  * Check with readelf after changing.
12  */
13 
14 #include <uapi/linux/time.h>
15 #include <asm/vgtod.h>
16 #include <asm/vvar.h>
17 #include <asm/unistd.h>
18 #include <asm/msr.h>
19 #include <asm/pvclock.h>
20 #include <asm/mshyperv.h>
21 #include <linux/math64.h>
22 #include <linux/time.h>
23 #include <linux/kernel.h>
24 
25 #define gtod (&VVAR(vsyscall_gtod_data))
26 
27 extern int __vdso_clock_gettime(clockid_t clock, struct timespec *ts);
28 extern int __vdso_gettimeofday(struct timeval *tv, struct timezone *tz);
29 extern time_t __vdso_time(time_t *t);
30 
31 #ifdef CONFIG_PARAVIRT_CLOCK
32 extern u8 pvclock_page
33 	__attribute__((visibility("hidden")));
34 #endif
35 
36 #ifdef CONFIG_HYPERV_TSCPAGE
37 extern u8 hvclock_page
38 	__attribute__((visibility("hidden")));
39 #endif
40 
41 #ifndef BUILD_VDSO32
42 
43 notrace static long vdso_fallback_gettime(long clock, struct timespec *ts)
44 {
45 	long ret;
46 	asm ("syscall" : "=a" (ret), "=m" (*ts) :
47 	     "0" (__NR_clock_gettime), "D" (clock), "S" (ts) :
48 	     "rcx", "r11");
49 	return ret;
50 }
51 
52 #else
53 
54 notrace static long vdso_fallback_gettime(long clock, struct timespec *ts)
55 {
56 	long ret;
57 
58 	asm (
59 		"mov %%ebx, %%edx \n"
60 		"mov %[clock], %%ebx \n"
61 		"call __kernel_vsyscall \n"
62 		"mov %%edx, %%ebx \n"
63 		: "=a" (ret), "=m" (*ts)
64 		: "0" (__NR_clock_gettime), [clock] "g" (clock), "c" (ts)
65 		: "edx");
66 	return ret;
67 }
68 
69 #endif
70 
71 #ifdef CONFIG_PARAVIRT_CLOCK
72 static notrace const struct pvclock_vsyscall_time_info *get_pvti0(void)
73 {
74 	return (const struct pvclock_vsyscall_time_info *)&pvclock_page;
75 }
76 
77 static notrace u64 vread_pvclock(void)
78 {
79 	const struct pvclock_vcpu_time_info *pvti = &get_pvti0()->pvti;
80 	u32 version;
81 	u64 ret;
82 
83 	/*
84 	 * Note: The kernel and hypervisor must guarantee that cpu ID
85 	 * number maps 1:1 to per-CPU pvclock time info.
86 	 *
87 	 * Because the hypervisor is entirely unaware of guest userspace
88 	 * preemption, it cannot guarantee that per-CPU pvclock time
89 	 * info is updated if the underlying CPU changes or that that
90 	 * version is increased whenever underlying CPU changes.
91 	 *
92 	 * On KVM, we are guaranteed that pvti updates for any vCPU are
93 	 * atomic as seen by *all* vCPUs.  This is an even stronger
94 	 * guarantee than we get with a normal seqlock.
95 	 *
96 	 * On Xen, we don't appear to have that guarantee, but Xen still
97 	 * supplies a valid seqlock using the version field.
98 	 *
99 	 * We only do pvclock vdso timing at all if
100 	 * PVCLOCK_TSC_STABLE_BIT is set, and we interpret that bit to
101 	 * mean that all vCPUs have matching pvti and that the TSC is
102 	 * synced, so we can just look at vCPU 0's pvti.
103 	 */
104 
105 	do {
106 		version = pvclock_read_begin(pvti);
107 
108 		if (unlikely(!(pvti->flags & PVCLOCK_TSC_STABLE_BIT)))
109 			return U64_MAX;
110 
111 		ret = __pvclock_read_cycles(pvti, rdtsc_ordered());
112 	} while (pvclock_read_retry(pvti, version));
113 
114 	return ret;
115 }
116 #endif
117 #ifdef CONFIG_HYPERV_TSCPAGE
118 static notrace u64 vread_hvclock(void)
119 {
120 	const struct ms_hyperv_tsc_page *tsc_pg =
121 		(const struct ms_hyperv_tsc_page *)&hvclock_page;
122 
123 	return hv_read_tsc_page(tsc_pg);
124 }
125 #endif
126 
127 notrace static inline u64 vgetcyc(int mode)
128 {
129 	if (mode == VCLOCK_TSC)
130 		return (u64)rdtsc_ordered();
131 #ifdef CONFIG_PARAVIRT_CLOCK
132 	else if (mode == VCLOCK_PVCLOCK)
133 		return vread_pvclock();
134 #endif
135 #ifdef CONFIG_HYPERV_TSCPAGE
136 	else if (mode == VCLOCK_HVCLOCK)
137 		return vread_hvclock();
138 #endif
139 	return U64_MAX;
140 }
141 
142 notrace static int do_hres(clockid_t clk, struct timespec *ts)
143 {
144 	struct vgtod_ts *base = &gtod->basetime[clk];
145 	u64 cycles, last, sec, ns;
146 	unsigned int seq;
147 
148 	do {
149 		seq = gtod_read_begin(gtod);
150 		cycles = vgetcyc(gtod->vclock_mode);
151 		ns = base->nsec;
152 		last = gtod->cycle_last;
153 		if (unlikely((s64)cycles < 0))
154 			return vdso_fallback_gettime(clk, ts);
155 		if (cycles > last)
156 			ns += (cycles - last) * gtod->mult;
157 		ns >>= gtod->shift;
158 		sec = base->sec;
159 	} while (unlikely(gtod_read_retry(gtod, seq)));
160 
161 	/*
162 	 * Do this outside the loop: a race inside the loop could result
163 	 * in __iter_div_u64_rem() being extremely slow.
164 	 */
165 	ts->tv_sec = sec + __iter_div_u64_rem(ns, NSEC_PER_SEC, &ns);
166 	ts->tv_nsec = ns;
167 
168 	return 0;
169 }
170 
171 notrace static void do_coarse(clockid_t clk, struct timespec *ts)
172 {
173 	struct vgtod_ts *base = &gtod->basetime[clk];
174 	unsigned int seq;
175 
176 	do {
177 		seq = gtod_read_begin(gtod);
178 		ts->tv_sec = base->sec;
179 		ts->tv_nsec = base->nsec;
180 	} while (unlikely(gtod_read_retry(gtod, seq)));
181 }
182 
183 notrace int __vdso_clock_gettime(clockid_t clock, struct timespec *ts)
184 {
185 	unsigned int msk;
186 
187 	/* Sort out negative (CPU/FD) and invalid clocks */
188 	if (unlikely((unsigned int) clock >= MAX_CLOCKS))
189 		return vdso_fallback_gettime(clock, ts);
190 
191 	/*
192 	 * Convert the clockid to a bitmask and use it to check which
193 	 * clocks are handled in the VDSO directly.
194 	 */
195 	msk = 1U << clock;
196 	if (likely(msk & VGTOD_HRES)) {
197 		return do_hres(clock, ts);
198 	} else if (msk & VGTOD_COARSE) {
199 		do_coarse(clock, ts);
200 		return 0;
201 	}
202 	return vdso_fallback_gettime(clock, ts);
203 }
204 
205 int clock_gettime(clockid_t, struct timespec *)
206 	__attribute__((weak, alias("__vdso_clock_gettime")));
207 
208 notrace int __vdso_gettimeofday(struct timeval *tv, struct timezone *tz)
209 {
210 	if (likely(tv != NULL)) {
211 		struct timespec *ts = (struct timespec *) tv;
212 
213 		do_hres(CLOCK_REALTIME, ts);
214 		tv->tv_usec /= 1000;
215 	}
216 	if (unlikely(tz != NULL)) {
217 		tz->tz_minuteswest = gtod->tz_minuteswest;
218 		tz->tz_dsttime = gtod->tz_dsttime;
219 	}
220 
221 	return 0;
222 }
223 int gettimeofday(struct timeval *, struct timezone *)
224 	__attribute__((weak, alias("__vdso_gettimeofday")));
225 
226 /*
227  * This will break when the xtime seconds get inaccurate, but that is
228  * unlikely
229  */
230 notrace time_t __vdso_time(time_t *t)
231 {
232 	/* This is atomic on x86 so we don't need any locks. */
233 	time_t result = READ_ONCE(gtod->basetime[CLOCK_REALTIME].sec);
234 
235 	if (t)
236 		*t = result;
237 	return result;
238 }
239 time_t time(time_t *t)
240 	__attribute__((weak, alias("__vdso_time")));
241