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Linux/arch/x86/vdso/vclock_gettime.c

  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/hpet.h>
 17 #include <asm/vvar.h>
 18 #include <asm/unistd.h>
 19 #include <asm/msr.h>
 20 #include <linux/math64.h>
 21 #include <linux/time.h>
 22 
 23 #define gtod (&VVAR(vsyscall_gtod_data))
 24 
 25 extern int __vdso_clock_gettime(clockid_t clock, struct timespec *ts);
 26 extern int __vdso_gettimeofday(struct timeval *tv, struct timezone *tz);
 27 extern time_t __vdso_time(time_t *t);
 28 
 29 #ifdef CONFIG_HPET_TIMER
 30 extern u8 hpet_page
 31         __attribute__((visibility("hidden")));
 32 
 33 static notrace cycle_t vread_hpet(void)
 34 {
 35         return *(const volatile u32 *)(&hpet_page + HPET_COUNTER);
 36 }
 37 #endif
 38 
 39 #ifndef BUILD_VDSO32
 40 
 41 #include <linux/kernel.h>
 42 #include <asm/vsyscall.h>
 43 #include <asm/fixmap.h>
 44 #include <asm/pvclock.h>
 45 
 46 notrace static long vdso_fallback_gettime(long clock, struct timespec *ts)
 47 {
 48         long ret;
 49         asm("syscall" : "=a" (ret) :
 50             "" (__NR_clock_gettime), "D" (clock), "S" (ts) : "memory");
 51         return ret;
 52 }
 53 
 54 notrace static long vdso_fallback_gtod(struct timeval *tv, struct timezone *tz)
 55 {
 56         long ret;
 57 
 58         asm("syscall" : "=a" (ret) :
 59             "" (__NR_gettimeofday), "D" (tv), "S" (tz) : "memory");
 60         return ret;
 61 }
 62 
 63 #ifdef CONFIG_PARAVIRT_CLOCK
 64 
 65 static notrace const struct pvclock_vsyscall_time_info *get_pvti(int cpu)
 66 {
 67         const struct pvclock_vsyscall_time_info *pvti_base;
 68         int idx = cpu / (PAGE_SIZE/PVTI_SIZE);
 69         int offset = cpu % (PAGE_SIZE/PVTI_SIZE);
 70 
 71         BUG_ON(PVCLOCK_FIXMAP_BEGIN + idx > PVCLOCK_FIXMAP_END);
 72 
 73         pvti_base = (struct pvclock_vsyscall_time_info *)
 74                     __fix_to_virt(PVCLOCK_FIXMAP_BEGIN+idx);
 75 
 76         return &pvti_base[offset];
 77 }
 78 
 79 static notrace cycle_t vread_pvclock(int *mode)
 80 {
 81         const struct pvclock_vsyscall_time_info *pvti;
 82         cycle_t ret;
 83         u64 last;
 84         u32 version;
 85         u8 flags;
 86         unsigned cpu, cpu1;
 87 
 88 
 89         /*
 90          * Note: hypervisor must guarantee that:
 91          * 1. cpu ID number maps 1:1 to per-CPU pvclock time info.
 92          * 2. that per-CPU pvclock time info is updated if the
 93          *    underlying CPU changes.
 94          * 3. that version is increased whenever underlying CPU
 95          *    changes.
 96          *
 97          */
 98         do {
 99                 cpu = __getcpu() & VGETCPU_CPU_MASK;
100                 /* TODO: We can put vcpu id into higher bits of pvti.version.
101                  * This will save a couple of cycles by getting rid of
102                  * __getcpu() calls (Gleb).
103                  */
104 
105                 pvti = get_pvti(cpu);
106 
107                 version = __pvclock_read_cycles(&pvti->pvti, &ret, &flags);
108 
109                 /*
110                  * Test we're still on the cpu as well as the version.
111                  * We could have been migrated just after the first
112                  * vgetcpu but before fetching the version, so we
113                  * wouldn't notice a version change.
114                  */
115                 cpu1 = __getcpu() & VGETCPU_CPU_MASK;
116         } while (unlikely(cpu != cpu1 ||
117                           (pvti->pvti.version & 1) ||
118                           pvti->pvti.version != version));
119 
120         if (unlikely(!(flags & PVCLOCK_TSC_STABLE_BIT)))
121                 *mode = VCLOCK_NONE;
122 
123         /* refer to tsc.c read_tsc() comment for rationale */
124         last = gtod->cycle_last;
125 
126         if (likely(ret >= last))
127                 return ret;
128 
129         return last;
130 }
131 #endif
132 
133 #else
134 
135 notrace static long vdso_fallback_gettime(long clock, struct timespec *ts)
136 {
137         long ret;
138 
139         asm(
140                 "mov %%ebx, %%edx \n"
141                 "mov %2, %%ebx \n"
142                 "call __kernel_vsyscall \n"
143                 "mov %%edx, %%ebx \n"
144                 : "=a" (ret)
145                 : "" (__NR_clock_gettime), "g" (clock), "c" (ts)
146                 : "memory", "edx");
147         return ret;
148 }
149 
150 notrace static long vdso_fallback_gtod(struct timeval *tv, struct timezone *tz)
151 {
152         long ret;
153 
154         asm(
155                 "mov %%ebx, %%edx \n"
156                 "mov %2, %%ebx \n"
157                 "call __kernel_vsyscall \n"
158                 "mov %%edx, %%ebx \n"
159                 : "=a" (ret)
160                 : "" (__NR_gettimeofday), "g" (tv), "c" (tz)
161                 : "memory", "edx");
162         return ret;
163 }
164 
165 #ifdef CONFIG_PARAVIRT_CLOCK
166 
167 static notrace cycle_t vread_pvclock(int *mode)
168 {
169         *mode = VCLOCK_NONE;
170         return 0;
171 }
172 #endif
173 
174 #endif
175 
176 notrace static cycle_t vread_tsc(void)
177 {
178         cycle_t ret;
179         u64 last;
180 
181         /*
182          * Empirically, a fence (of type that depends on the CPU)
183          * before rdtsc is enough to ensure that rdtsc is ordered
184          * with respect to loads.  The various CPU manuals are unclear
185          * as to whether rdtsc can be reordered with later loads,
186          * but no one has ever seen it happen.
187          */
188         rdtsc_barrier();
189         ret = (cycle_t)__native_read_tsc();
190 
191         last = gtod->cycle_last;
192 
193         if (likely(ret >= last))
194                 return ret;
195 
196         /*
197          * GCC likes to generate cmov here, but this branch is extremely
198          * predictable (it's just a funciton of time and the likely is
199          * very likely) and there's a data dependence, so force GCC
200          * to generate a branch instead.  I don't barrier() because
201          * we don't actually need a barrier, and if this function
202          * ever gets inlined it will generate worse code.
203          */
204         asm volatile ("");
205         return last;
206 }
207 
208 notrace static inline u64 vgetsns(int *mode)
209 {
210         u64 v;
211         cycles_t cycles;
212 
213         if (gtod->vclock_mode == VCLOCK_TSC)
214                 cycles = vread_tsc();
215 #ifdef CONFIG_HPET_TIMER
216         else if (gtod->vclock_mode == VCLOCK_HPET)
217                 cycles = vread_hpet();
218 #endif
219 #ifdef CONFIG_PARAVIRT_CLOCK
220         else if (gtod->vclock_mode == VCLOCK_PVCLOCK)
221                 cycles = vread_pvclock(mode);
222 #endif
223         else
224                 return 0;
225         v = (cycles - gtod->cycle_last) & gtod->mask;
226         return v * gtod->mult;
227 }
228 
229 /* Code size doesn't matter (vdso is 4k anyway) and this is faster. */
230 notrace static int __always_inline do_realtime(struct timespec *ts)
231 {
232         unsigned long seq;
233         u64 ns;
234         int mode;
235 
236         do {
237                 seq = gtod_read_begin(gtod);
238                 mode = gtod->vclock_mode;
239                 ts->tv_sec = gtod->wall_time_sec;
240                 ns = gtod->wall_time_snsec;
241                 ns += vgetsns(&mode);
242                 ns >>= gtod->shift;
243         } while (unlikely(gtod_read_retry(gtod, seq)));
244 
245         ts->tv_sec += __iter_div_u64_rem(ns, NSEC_PER_SEC, &ns);
246         ts->tv_nsec = ns;
247 
248         return mode;
249 }
250 
251 notrace static int __always_inline do_monotonic(struct timespec *ts)
252 {
253         unsigned long seq;
254         u64 ns;
255         int mode;
256 
257         do {
258                 seq = gtod_read_begin(gtod);
259                 mode = gtod->vclock_mode;
260                 ts->tv_sec = gtod->monotonic_time_sec;
261                 ns = gtod->monotonic_time_snsec;
262                 ns += vgetsns(&mode);
263                 ns >>= gtod->shift;
264         } while (unlikely(gtod_read_retry(gtod, seq)));
265 
266         ts->tv_sec += __iter_div_u64_rem(ns, NSEC_PER_SEC, &ns);
267         ts->tv_nsec = ns;
268 
269         return mode;
270 }
271 
272 notrace static void do_realtime_coarse(struct timespec *ts)
273 {
274         unsigned long seq;
275         do {
276                 seq = gtod_read_begin(gtod);
277                 ts->tv_sec = gtod->wall_time_coarse_sec;
278                 ts->tv_nsec = gtod->wall_time_coarse_nsec;
279         } while (unlikely(gtod_read_retry(gtod, seq)));
280 }
281 
282 notrace static void do_monotonic_coarse(struct timespec *ts)
283 {
284         unsigned long seq;
285         do {
286                 seq = gtod_read_begin(gtod);
287                 ts->tv_sec = gtod->monotonic_time_coarse_sec;
288                 ts->tv_nsec = gtod->monotonic_time_coarse_nsec;
289         } while (unlikely(gtod_read_retry(gtod, seq)));
290 }
291 
292 notrace int __vdso_clock_gettime(clockid_t clock, struct timespec *ts)
293 {
294         switch (clock) {
295         case CLOCK_REALTIME:
296                 if (do_realtime(ts) == VCLOCK_NONE)
297                         goto fallback;
298                 break;
299         case CLOCK_MONOTONIC:
300                 if (do_monotonic(ts) == VCLOCK_NONE)
301                         goto fallback;
302                 break;
303         case CLOCK_REALTIME_COARSE:
304                 do_realtime_coarse(ts);
305                 break;
306         case CLOCK_MONOTONIC_COARSE:
307                 do_monotonic_coarse(ts);
308                 break;
309         default:
310                 goto fallback;
311         }
312 
313         return 0;
314 fallback:
315         return vdso_fallback_gettime(clock, ts);
316 }
317 int clock_gettime(clockid_t, struct timespec *)
318         __attribute__((weak, alias("__vdso_clock_gettime")));
319 
320 notrace int __vdso_gettimeofday(struct timeval *tv, struct timezone *tz)
321 {
322         if (likely(tv != NULL)) {
323                 if (unlikely(do_realtime((struct timespec *)tv) == VCLOCK_NONE))
324                         return vdso_fallback_gtod(tv, tz);
325                 tv->tv_usec /= 1000;
326         }
327         if (unlikely(tz != NULL)) {
328                 tz->tz_minuteswest = gtod->tz_minuteswest;
329                 tz->tz_dsttime = gtod->tz_dsttime;
330         }
331 
332         return 0;
333 }
334 int gettimeofday(struct timeval *, struct timezone *)
335         __attribute__((weak, alias("__vdso_gettimeofday")));
336 
337 /*
338  * This will break when the xtime seconds get inaccurate, but that is
339  * unlikely
340  */
341 notrace time_t __vdso_time(time_t *t)
342 {
343         /* This is atomic on x86 so we don't need any locks. */
344         time_t result = ACCESS_ONCE(gtod->wall_time_sec);
345 
346         if (t)
347                 *t = result;
348         return result;
349 }
350 int time(time_t *t)
351         __attribute__((weak, alias("__vdso_time")));
352 

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