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