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// SPDX-License-Identifier: GPL-2.0-only
/*
* Copyright 2006 Andi Kleen, SUSE Labs.
*
* Fast user context implementation of clock_gettime, gettimeofday, and time.
*
* 32 Bit compat layer by Stefani Seibold <stefani@seibold.net>
* sponsored by Rohde & Schwarz GmbH & Co. KG Munich/Germany
*
* The code should have no internal unresolved relocations.
* Check with readelf after changing.
*/
#include <uapi/linux/time.h>
#include <asm/vgtod.h>
#include <asm/vvar.h>
#include <asm/unistd.h>
#include <asm/msr.h>
#include <asm/pvclock.h>
#include <asm/mshyperv.h>
#include <linux/math64.h>
#include <linux/time.h>
#include <linux/kernel.h>
#define gtod (&VVAR(vsyscall_gtod_data))
extern int __vdso_clock_gettime(clockid_t clock, struct timespec *ts);
extern int __vdso_gettimeofday(struct timeval *tv, struct timezone *tz);
extern time_t __vdso_time(time_t *t);
#ifdef CONFIG_PARAVIRT_CLOCK
extern u8 pvclock_page[PAGE_SIZE]
__attribute__((visibility("hidden")));
#endif
#ifdef CONFIG_HYPERV_TSCPAGE
extern u8 hvclock_page[PAGE_SIZE]
__attribute__((visibility("hidden")));
#endif
#ifndef BUILD_VDSO32
notrace static long vdso_fallback_gettime(long clock, struct timespec *ts)
{
long ret;
asm ("syscall" : "=a" (ret), "=m" (*ts) :
"0" (__NR_clock_gettime), "D" (clock), "S" (ts) :
"rcx", "r11");
return ret;
}
#else
notrace static long vdso_fallback_gettime(long clock, struct timespec *ts)
{
long ret;
asm (
"mov %%ebx, %%edx \n"
"mov %[clock], %%ebx \n"
"call __kernel_vsyscall \n"
"mov %%edx, %%ebx \n"
: "=a" (ret), "=m" (*ts)
: "0" (__NR_clock_gettime), [clock] "g" (clock), "c" (ts)
: "edx");
return ret;
}
#endif
#ifdef CONFIG_PARAVIRT_CLOCK
static notrace const struct pvclock_vsyscall_time_info *get_pvti0(void)
{
return (const struct pvclock_vsyscall_time_info *)&pvclock_page;
}
static notrace u64 vread_pvclock(void)
{
const struct pvclock_vcpu_time_info *pvti = &get_pvti0()->pvti;
u32 version;
u64 ret;
/*
* Note: The kernel and hypervisor must guarantee that cpu ID
* number maps 1:1 to per-CPU pvclock time info.
*
* Because the hypervisor is entirely unaware of guest userspace
* preemption, it cannot guarantee that per-CPU pvclock time
* info is updated if the underlying CPU changes or that that
* version is increased whenever underlying CPU changes.
*
* On KVM, we are guaranteed that pvti updates for any vCPU are
* atomic as seen by *all* vCPUs. This is an even stronger
* guarantee than we get with a normal seqlock.
*
* On Xen, we don't appear to have that guarantee, but Xen still
* supplies a valid seqlock using the version field.
*
* We only do pvclock vdso timing at all if
* PVCLOCK_TSC_STABLE_BIT is set, and we interpret that bit to
* mean that all vCPUs have matching pvti and that the TSC is
* synced, so we can just look at vCPU 0's pvti.
*/
do {
version = pvclock_read_begin(pvti);
if (unlikely(!(pvti->flags & PVCLOCK_TSC_STABLE_BIT)))
return U64_MAX;
ret = __pvclock_read_cycles(pvti, rdtsc_ordered());
} while (pvclock_read_retry(pvti, version));
return ret;
}
#endif
#ifdef CONFIG_HYPERV_TSCPAGE
static notrace u64 vread_hvclock(void)
{
const struct ms_hyperv_tsc_page *tsc_pg =
(const struct ms_hyperv_tsc_page *)&hvclock_page;
return hv_read_tsc_page(tsc_pg);
}
#endif
notrace static inline u64 vgetcyc(int mode)
{
if (mode == VCLOCK_TSC)
return (u64)rdtsc_ordered();
#ifdef CONFIG_PARAVIRT_CLOCK
else if (mode == VCLOCK_PVCLOCK)
return vread_pvclock();
#endif
#ifdef CONFIG_HYPERV_TSCPAGE
else if (mode == VCLOCK_HVCLOCK)
return vread_hvclock();
#endif
return U64_MAX;
}
notrace static int do_hres(clockid_t clk, struct timespec *ts)
{
struct vgtod_ts *base = >od->basetime[clk];
u64 cycles, last, sec, ns;
unsigned int seq;
do {
seq = gtod_read_begin(gtod);
cycles = vgetcyc(gtod->vclock_mode);
ns = base->nsec;
last = gtod->cycle_last;
if (unlikely((s64)cycles < 0))
return vdso_fallback_gettime(clk, ts);
if (cycles > last)
ns += (cycles - last) * gtod->mult;
ns >>= gtod->shift;
sec = base->sec;
} while (unlikely(gtod_read_retry(gtod, seq)));
/*
* Do this outside the loop: a race inside the loop could result
* in __iter_div_u64_rem() being extremely slow.
*/
ts->tv_sec = sec + __iter_div_u64_rem(ns, NSEC_PER_SEC, &ns);
ts->tv_nsec = ns;
return 0;
}
notrace static void do_coarse(clockid_t clk, struct timespec *ts)
{
struct vgtod_ts *base = >od->basetime[clk];
unsigned int seq;
do {
seq = gtod_read_begin(gtod);
ts->tv_sec = base->sec;
ts->tv_nsec = base->nsec;
} while (unlikely(gtod_read_retry(gtod, seq)));
}
notrace int __vdso_clock_gettime(clockid_t clock, struct timespec *ts)
{
unsigned int msk;
/* Sort out negative (CPU/FD) and invalid clocks */
if (unlikely((unsigned int) clock >= MAX_CLOCKS))
return vdso_fallback_gettime(clock, ts);
/*
* Convert the clockid to a bitmask and use it to check which
* clocks are handled in the VDSO directly.
*/
msk = 1U << clock;
if (likely(msk & VGTOD_HRES)) {
return do_hres(clock, ts);
} else if (msk & VGTOD_COARSE) {
do_coarse(clock, ts);
return 0;
}
return vdso_fallback_gettime(clock, ts);
}
int clock_gettime(clockid_t, struct timespec *)
__attribute__((weak, alias("__vdso_clock_gettime")));
notrace int __vdso_gettimeofday(struct timeval *tv, struct timezone *tz)
{
if (likely(tv != NULL)) {
struct timespec *ts = (struct timespec *) tv;
do_hres(CLOCK_REALTIME, ts);
tv->tv_usec /= 1000;
}
if (unlikely(tz != NULL)) {
tz->tz_minuteswest = gtod->tz_minuteswest;
tz->tz_dsttime = gtod->tz_dsttime;
}
return 0;
}
int gettimeofday(struct timeval *, struct timezone *)
__attribute__((weak, alias("__vdso_gettimeofday")));
/*
* This will break when the xtime seconds get inaccurate, but that is
* unlikely
*/
notrace time_t __vdso_time(time_t *t)
{
/* This is atomic on x86 so we don't need any locks. */
time_t result = READ_ONCE(gtod->basetime[CLOCK_REALTIME].sec);
if (t)
*t = result;
return result;
}
time_t time(time_t *t)
__attribute__((weak, alias("__vdso_time")));
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