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 */ 47 extern struct pvclock_vsyscall_time_info pvclock_page 48 __attribute__((visibility("hidden"))); 49 #endif 50 51 #ifdef CONFIG_HYPERV_TIMER 52 extern struct ms_hyperv_tsc_page hvclock_page 53 __attribute__((visibility("hidden"))); 54 #endif 55 56 #ifndef BUILD_VDSO32 57 58 static __always_inline 59 long 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 70 static __always_inline 71 long 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 82 static __always_inline 83 long 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 96 static __always_inline 97 long 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 } 112 113 static __always_inline 114 long 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 } 129 130 static __always_inline 131 long 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 } 147 148 static __always_inline long 149 clock_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 } 164 165 static __always_inline 166 long 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 185 static 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 227 static 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 237 238 static 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 } 263 264 static 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 */ 279 static 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 */ 303 static __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 */ 337