329 lines
7.8 KiB
C
329 lines
7.8 KiB
C
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/*
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* Copyright 2006 Andi Kleen, SUSE Labs.
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* Subject to the GNU Public License, v.2
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*
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* Fast user context implementation of clock_gettime, gettimeofday, and time.
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*
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* 32 Bit compat layer by Stefani Seibold <stefani@seibold.net>
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* sponsored by Rohde & Schwarz GmbH & Co. KG Munich/Germany
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*
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* The code should have no internal unresolved relocations.
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* Check with readelf after changing.
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*/
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#include <uapi/linux/time.h>
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#include <asm/vgtod.h>
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#include <asm/vvar.h>
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#include <asm/unistd.h>
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#include <asm/msr.h>
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#include <asm/pvclock.h>
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#include <asm/mshyperv.h>
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#include <linux/math64.h>
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#include <linux/time.h>
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#include <linux/kernel.h>
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#define gtod (&VVAR(vsyscall_gtod_data))
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extern int __vdso_clock_gettime(clockid_t clock, struct timespec *ts);
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extern int __vdso_gettimeofday(struct timeval *tv, struct timezone *tz);
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extern time_t __vdso_time(time_t *t);
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#ifdef CONFIG_PARAVIRT_CLOCK
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extern u8 pvclock_page
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__attribute__((visibility("hidden")));
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#endif
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#ifdef CONFIG_HYPERV_TSCPAGE
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extern u8 hvclock_page
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__attribute__((visibility("hidden")));
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#endif
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#ifndef BUILD_VDSO32
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notrace static long vdso_fallback_gettime(long clock, struct timespec *ts)
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{
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long ret;
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asm("syscall" : "=a" (ret) :
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"0" (__NR_clock_gettime), "D" (clock), "S" (ts) : "memory");
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return ret;
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}
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notrace static long vdso_fallback_gtod(struct timeval *tv, struct timezone *tz)
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{
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long ret;
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asm("syscall" : "=a" (ret) :
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"0" (__NR_gettimeofday), "D" (tv), "S" (tz) : "memory");
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return ret;
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}
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#else
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notrace static long vdso_fallback_gettime(long clock, struct timespec *ts)
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{
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long ret;
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asm(
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"mov %%ebx, %%edx \n"
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"mov %2, %%ebx \n"
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"call __kernel_vsyscall \n"
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"mov %%edx, %%ebx \n"
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: "=a" (ret)
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: "0" (__NR_clock_gettime), "g" (clock), "c" (ts)
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: "memory", "edx");
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return ret;
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}
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notrace static long vdso_fallback_gtod(struct timeval *tv, struct timezone *tz)
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{
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long ret;
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asm(
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"mov %%ebx, %%edx \n"
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"mov %2, %%ebx \n"
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"call __kernel_vsyscall \n"
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"mov %%edx, %%ebx \n"
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: "=a" (ret)
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: "0" (__NR_gettimeofday), "g" (tv), "c" (tz)
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: "memory", "edx");
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return ret;
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}
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#endif
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#ifdef CONFIG_PARAVIRT_CLOCK
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static notrace const struct pvclock_vsyscall_time_info *get_pvti0(void)
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{
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return (const struct pvclock_vsyscall_time_info *)&pvclock_page;
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}
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static notrace u64 vread_pvclock(int *mode)
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{
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const struct pvclock_vcpu_time_info *pvti = &get_pvti0()->pvti;
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u64 ret;
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u64 last;
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u32 version;
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/*
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* Note: The kernel and hypervisor must guarantee that cpu ID
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* number maps 1:1 to per-CPU pvclock time info.
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*
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* Because the hypervisor is entirely unaware of guest userspace
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* preemption, it cannot guarantee that per-CPU pvclock time
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* info is updated if the underlying CPU changes or that that
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* version is increased whenever underlying CPU changes.
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*
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* On KVM, we are guaranteed that pvti updates for any vCPU are
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* atomic as seen by *all* vCPUs. This is an even stronger
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* guarantee than we get with a normal seqlock.
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*
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* On Xen, we don't appear to have that guarantee, but Xen still
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* supplies a valid seqlock using the version field.
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*
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* We only do pvclock vdso timing at all if
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* PVCLOCK_TSC_STABLE_BIT is set, and we interpret that bit to
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* mean that all vCPUs have matching pvti and that the TSC is
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* synced, so we can just look at vCPU 0's pvti.
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*/
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do {
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version = pvclock_read_begin(pvti);
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if (unlikely(!(pvti->flags & PVCLOCK_TSC_STABLE_BIT))) {
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*mode = VCLOCK_NONE;
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return 0;
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}
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ret = __pvclock_read_cycles(pvti, rdtsc_ordered());
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} while (pvclock_read_retry(pvti, version));
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/* refer to vread_tsc() comment for rationale */
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last = gtod->cycle_last;
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if (likely(ret >= last))
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return ret;
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return last;
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}
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#endif
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#ifdef CONFIG_HYPERV_TSCPAGE
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static notrace u64 vread_hvclock(int *mode)
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{
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const struct ms_hyperv_tsc_page *tsc_pg =
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(const struct ms_hyperv_tsc_page *)&hvclock_page;
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u64 current_tick = hv_read_tsc_page(tsc_pg);
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if (current_tick != U64_MAX)
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return current_tick;
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*mode = VCLOCK_NONE;
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return 0;
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}
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#endif
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notrace static u64 vread_tsc(void)
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{
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u64 ret = (u64)rdtsc_ordered();
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u64 last = gtod->cycle_last;
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if (likely(ret >= last))
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return ret;
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/*
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* GCC likes to generate cmov here, but this branch is extremely
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* predictable (it's just a function of time and the likely is
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* very likely) and there's a data dependence, so force GCC
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* to generate a branch instead. I don't barrier() because
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* we don't actually need a barrier, and if this function
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* ever gets inlined it will generate worse code.
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*/
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asm volatile ("");
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return last;
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}
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notrace static inline u64 vgetsns(int *mode)
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{
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u64 v;
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cycles_t cycles;
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if (gtod->vclock_mode == VCLOCK_TSC)
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cycles = vread_tsc();
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#ifdef CONFIG_PARAVIRT_CLOCK
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else if (gtod->vclock_mode == VCLOCK_PVCLOCK)
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cycles = vread_pvclock(mode);
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#endif
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#ifdef CONFIG_HYPERV_TSCPAGE
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else if (gtod->vclock_mode == VCLOCK_HVCLOCK)
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cycles = vread_hvclock(mode);
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#endif
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else
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return 0;
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v = (cycles - gtod->cycle_last) & gtod->mask;
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return v * gtod->mult;
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}
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/* Code size doesn't matter (vdso is 4k anyway) and this is faster. */
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notrace static int __always_inline do_realtime(struct timespec *ts)
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{
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unsigned long seq;
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u64 ns;
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int mode;
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do {
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seq = gtod_read_begin(gtod);
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mode = gtod->vclock_mode;
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ts->tv_sec = gtod->wall_time_sec;
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ns = gtod->wall_time_snsec;
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ns += vgetsns(&mode);
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ns >>= gtod->shift;
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} while (unlikely(gtod_read_retry(gtod, seq)));
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ts->tv_sec += __iter_div_u64_rem(ns, NSEC_PER_SEC, &ns);
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ts->tv_nsec = ns;
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return mode;
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}
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notrace static int __always_inline do_monotonic(struct timespec *ts)
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{
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unsigned long seq;
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u64 ns;
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int mode;
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do {
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seq = gtod_read_begin(gtod);
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mode = gtod->vclock_mode;
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ts->tv_sec = gtod->monotonic_time_sec;
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ns = gtod->monotonic_time_snsec;
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ns += vgetsns(&mode);
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ns >>= gtod->shift;
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} while (unlikely(gtod_read_retry(gtod, seq)));
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ts->tv_sec += __iter_div_u64_rem(ns, NSEC_PER_SEC, &ns);
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ts->tv_nsec = ns;
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return mode;
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}
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notrace static void do_realtime_coarse(struct timespec *ts)
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{
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unsigned long seq;
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do {
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seq = gtod_read_begin(gtod);
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ts->tv_sec = gtod->wall_time_coarse_sec;
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ts->tv_nsec = gtod->wall_time_coarse_nsec;
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} while (unlikely(gtod_read_retry(gtod, seq)));
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}
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notrace static void do_monotonic_coarse(struct timespec *ts)
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{
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unsigned long seq;
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do {
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seq = gtod_read_begin(gtod);
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ts->tv_sec = gtod->monotonic_time_coarse_sec;
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ts->tv_nsec = gtod->monotonic_time_coarse_nsec;
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} while (unlikely(gtod_read_retry(gtod, seq)));
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}
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notrace int __vdso_clock_gettime(clockid_t clock, struct timespec *ts)
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{
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switch (clock) {
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case CLOCK_REALTIME:
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if (do_realtime(ts) == VCLOCK_NONE)
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goto fallback;
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break;
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case CLOCK_MONOTONIC:
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if (do_monotonic(ts) == VCLOCK_NONE)
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goto fallback;
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break;
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case CLOCK_REALTIME_COARSE:
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do_realtime_coarse(ts);
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break;
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case CLOCK_MONOTONIC_COARSE:
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do_monotonic_coarse(ts);
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break;
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default:
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goto fallback;
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}
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return 0;
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fallback:
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return vdso_fallback_gettime(clock, ts);
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}
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int clock_gettime(clockid_t, struct timespec *)
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__attribute__((weak, alias("__vdso_clock_gettime")));
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notrace int __vdso_gettimeofday(struct timeval *tv, struct timezone *tz)
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{
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if (likely(tv != NULL)) {
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if (unlikely(do_realtime((struct timespec *)tv) == VCLOCK_NONE))
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return vdso_fallback_gtod(tv, tz);
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tv->tv_usec /= 1000;
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}
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if (unlikely(tz != NULL)) {
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tz->tz_minuteswest = gtod->tz_minuteswest;
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tz->tz_dsttime = gtod->tz_dsttime;
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}
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return 0;
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}
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int gettimeofday(struct timeval *, struct timezone *)
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__attribute__((weak, alias("__vdso_gettimeofday")));
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/*
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* This will break when the xtime seconds get inaccurate, but that is
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* unlikely
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*/
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notrace time_t __vdso_time(time_t *t)
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{
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/* This is atomic on x86 so we don't need any locks. */
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time_t result = READ_ONCE(gtod->wall_time_sec);
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if (t)
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*t = result;
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return result;
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}
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time_t time(time_t *t)
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__attribute__((weak, alias("__vdso_time")));
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