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Merge branch 'x86-vdso-for-linus' of git://git.kernel.org/pub/scm/lin…
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…ux/kernel/git/tip/tip

Pull x86 vdso updates from Ingo Molnar:
 "Two main changes:

   - Cleanups, simplifications and CLOCK_TAI support (Thomas Gleixner)

   - Improve code generation (Andy Lutomirski)"

* 'x86-vdso-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/vdso: Rearrange do_hres() to improve code generation
  x86/vdso: Document vgtod_ts better
  x86/vdso: Remove "memory" clobbers in the vDSO syscall fallbacks
  x66/vdso: Add CLOCK_TAI support
  x86/vdso: Move cycle_last handling into the caller
  x86/vdso: Simplify the invalid vclock case
  x86/vdso: Replace the clockid switch case
  x86/vdso: Collapse coarse functions
  x86/vdso: Collapse high resolution functions
  x86/vdso: Introduce and use vgtod_ts
  x86/vdso: Use unsigned int consistently for vsyscall_gtod_data:: Seq
  x86/vdso: Enforce 64bit clocksource
  x86/time: Implement clocksource_arch_init()
  clocksource: Provide clocksource_arch_init()
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Linus Torvalds committed Oct 23, 2018
2 parents d82924c + 99c19e6 commit 034bda1
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Showing 8 changed files with 155 additions and 193 deletions.
1 change: 1 addition & 0 deletions arch/x86/Kconfig
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Original file line number Diff line number Diff line change
Expand Up @@ -48,6 +48,7 @@ config X86
select ACPI_SYSTEM_POWER_STATES_SUPPORT if ACPI
select ANON_INODES
select ARCH_CLOCKSOURCE_DATA
select ARCH_CLOCKSOURCE_INIT
select ARCH_DISCARD_MEMBLOCK
select ARCH_HAS_ACPI_TABLE_UPGRADE if ACPI
select ARCH_HAS_DEBUG_VIRTUAL
Expand Down
210 changes: 60 additions & 150 deletions arch/x86/entry/vdso/vclock_gettime.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -45,21 +45,10 @@ 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) :
"memory", "rcx", "r11");
"rcx", "r11");
return ret;
}

notrace static long vdso_fallback_gtod(struct timeval *tv, struct timezone *tz)
{
long ret;

asm ("syscall" : "=a" (ret), "=m" (*tv), "=m" (*tz) :
"0" (__NR_gettimeofday), "D" (tv), "S" (tz) :
"memory", "rcx", "r11");
return ret;
}


#else

notrace static long vdso_fallback_gettime(long clock, struct timespec *ts)
Expand All @@ -73,22 +62,7 @@ notrace static long vdso_fallback_gettime(long clock, struct timespec *ts)
"mov %%edx, %%ebx \n"
: "=a" (ret), "=m" (*ts)
: "0" (__NR_clock_gettime), [clock] "g" (clock), "c" (ts)
: "memory", "edx");
return ret;
}

notrace static long vdso_fallback_gtod(struct timeval *tv, struct timezone *tz)
{
long ret;

asm (
"mov %%ebx, %%edx \n"
"mov %[tv], %%ebx \n"
"call __kernel_vsyscall \n"
"mov %%edx, %%ebx \n"
: "=a" (ret), "=m" (*tv), "=m" (*tz)
: "0" (__NR_gettimeofday), [tv] "g" (tv), "c" (tz)
: "memory", "edx");
: "edx");
return ret;
}

Expand All @@ -100,12 +74,11 @@ 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(int *mode)
static notrace u64 vread_pvclock(void)
{
const struct pvclock_vcpu_time_info *pvti = &get_pvti0()->pvti;
u64 ret;
u64 last;
u32 version;
u64 ret;

/*
* Note: The kernel and hypervisor must guarantee that cpu ID
Expand All @@ -132,175 +105,112 @@ static notrace u64 vread_pvclock(int *mode)
do {
version = pvclock_read_begin(pvti);

if (unlikely(!(pvti->flags & PVCLOCK_TSC_STABLE_BIT))) {
*mode = VCLOCK_NONE;
return 0;
}
if (unlikely(!(pvti->flags & PVCLOCK_TSC_STABLE_BIT)))
return U64_MAX;

ret = __pvclock_read_cycles(pvti, rdtsc_ordered());
} while (pvclock_read_retry(pvti, version));

/* refer to vread_tsc() comment for rationale */
last = gtod->cycle_last;

if (likely(ret >= last))
return ret;

return last;
return ret;
}
#endif
#ifdef CONFIG_HYPERV_TSCPAGE
static notrace u64 vread_hvclock(int *mode)
static notrace u64 vread_hvclock(void)
{
const struct ms_hyperv_tsc_page *tsc_pg =
(const struct ms_hyperv_tsc_page *)&hvclock_page;
u64 current_tick = hv_read_tsc_page(tsc_pg);

if (current_tick != U64_MAX)
return current_tick;

*mode = VCLOCK_NONE;
return 0;
return hv_read_tsc_page(tsc_pg);
}
#endif

notrace static u64 vread_tsc(void)
notrace static inline u64 vgetcyc(int mode)
{
u64 ret = (u64)rdtsc_ordered();
u64 last = gtod->cycle_last;

if (likely(ret >= last))
return ret;

/*
* GCC likes to generate cmov here, but this branch is extremely
* predictable (it's just a function of time and the likely is
* very likely) and there's a data dependence, so force GCC
* to generate a branch instead. I don't barrier() because
* we don't actually need a barrier, and if this function
* ever gets inlined it will generate worse code.
*/
asm volatile ("");
return last;
}

notrace static inline u64 vgetsns(int *mode)
{
u64 v;
cycles_t cycles;

if (gtod->vclock_mode == VCLOCK_TSC)
cycles = vread_tsc();
if (mode == VCLOCK_TSC)
return (u64)rdtsc_ordered();
#ifdef CONFIG_PARAVIRT_CLOCK
else if (gtod->vclock_mode == VCLOCK_PVCLOCK)
cycles = vread_pvclock(mode);
else if (mode == VCLOCK_PVCLOCK)
return vread_pvclock();
#endif
#ifdef CONFIG_HYPERV_TSCPAGE
else if (gtod->vclock_mode == VCLOCK_HVCLOCK)
cycles = vread_hvclock(mode);
else if (mode == VCLOCK_HVCLOCK)
return vread_hvclock();
#endif
else
return 0;
v = (cycles - gtod->cycle_last) & gtod->mask;
return v * gtod->mult;
return U64_MAX;
}

/* Code size doesn't matter (vdso is 4k anyway) and this is faster. */
notrace static int __always_inline do_realtime(struct timespec *ts)
notrace static int do_hres(clockid_t clk, struct timespec *ts)
{
unsigned long seq;
u64 ns;
int mode;
struct vgtod_ts *base = &gtod->basetime[clk];
u64 cycles, last, sec, ns;
unsigned int seq;

do {
seq = gtod_read_begin(gtod);
mode = gtod->vclock_mode;
ts->tv_sec = gtod->wall_time_sec;
ns = gtod->wall_time_snsec;
ns += vgetsns(&mode);
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)));

ts->tv_sec += __iter_div_u64_rem(ns, NSEC_PER_SEC, &ns);
/*
* 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 mode;
return 0;
}

notrace static int __always_inline do_monotonic(struct timespec *ts)
notrace static void do_coarse(clockid_t clk, struct timespec *ts)
{
unsigned long seq;
u64 ns;
int mode;
struct vgtod_ts *base = &gtod->basetime[clk];
unsigned int seq;

do {
seq = gtod_read_begin(gtod);
mode = gtod->vclock_mode;
ts->tv_sec = gtod->monotonic_time_sec;
ns = gtod->monotonic_time_snsec;
ns += vgetsns(&mode);
ns >>= gtod->shift;
ts->tv_sec = base->sec;
ts->tv_nsec = base->nsec;
} while (unlikely(gtod_read_retry(gtod, seq)));

ts->tv_sec += __iter_div_u64_rem(ns, NSEC_PER_SEC, &ns);
ts->tv_nsec = ns;

return mode;
}

notrace static void do_realtime_coarse(struct timespec *ts)
notrace int __vdso_clock_gettime(clockid_t clock, struct timespec *ts)
{
unsigned long seq;
do {
seq = gtod_read_begin(gtod);
ts->tv_sec = gtod->wall_time_coarse_sec;
ts->tv_nsec = gtod->wall_time_coarse_nsec;
} while (unlikely(gtod_read_retry(gtod, seq)));
}
unsigned int msk;

notrace static void do_monotonic_coarse(struct timespec *ts)
{
unsigned long seq;
do {
seq = gtod_read_begin(gtod);
ts->tv_sec = gtod->monotonic_time_coarse_sec;
ts->tv_nsec = gtod->monotonic_time_coarse_nsec;
} while (unlikely(gtod_read_retry(gtod, seq)));
}
/* Sort out negative (CPU/FD) and invalid clocks */
if (unlikely((unsigned int) clock >= MAX_CLOCKS))
return vdso_fallback_gettime(clock, ts);

notrace int __vdso_clock_gettime(clockid_t clock, struct timespec *ts)
{
switch (clock) {
case CLOCK_REALTIME:
if (do_realtime(ts) == VCLOCK_NONE)
goto fallback;
break;
case CLOCK_MONOTONIC:
if (do_monotonic(ts) == VCLOCK_NONE)
goto fallback;
break;
case CLOCK_REALTIME_COARSE:
do_realtime_coarse(ts);
break;
case CLOCK_MONOTONIC_COARSE:
do_monotonic_coarse(ts);
break;
default:
goto fallback;
/*
* 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 0;
fallback:
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)) {
if (unlikely(do_realtime((struct timespec *)tv) == VCLOCK_NONE))
return vdso_fallback_gtod(tv, tz);
struct timespec *ts = (struct timespec *) tv;

do_hres(CLOCK_REALTIME, ts);
tv->tv_usec /= 1000;
}
if (unlikely(tz != NULL)) {
Expand All @@ -320,7 +230,7 @@ int gettimeofday(struct timeval *, struct timezone *)
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->wall_time_sec);
time_t result = READ_ONCE(gtod->basetime[CLOCK_REALTIME].sec);

if (t)
*t = result;
Expand Down
51 changes: 28 additions & 23 deletions arch/x86/entry/vsyscall/vsyscall_gtod.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -31,6 +31,8 @@ void update_vsyscall(struct timekeeper *tk)
{
int vclock_mode = tk->tkr_mono.clock->archdata.vclock_mode;
struct vsyscall_gtod_data *vdata = &vsyscall_gtod_data;
struct vgtod_ts *base;
u64 nsec;

/* Mark the new vclock used. */
BUILD_BUG_ON(VCLOCK_MAX >= 32);
Expand All @@ -45,34 +47,37 @@ void update_vsyscall(struct timekeeper *tk)
vdata->mult = tk->tkr_mono.mult;
vdata->shift = tk->tkr_mono.shift;

vdata->wall_time_sec = tk->xtime_sec;
vdata->wall_time_snsec = tk->tkr_mono.xtime_nsec;
base = &vdata->basetime[CLOCK_REALTIME];
base->sec = tk->xtime_sec;
base->nsec = tk->tkr_mono.xtime_nsec;

vdata->monotonic_time_sec = tk->xtime_sec
+ tk->wall_to_monotonic.tv_sec;
vdata->monotonic_time_snsec = tk->tkr_mono.xtime_nsec
+ ((u64)tk->wall_to_monotonic.tv_nsec
<< tk->tkr_mono.shift);
while (vdata->monotonic_time_snsec >=
(((u64)NSEC_PER_SEC) << tk->tkr_mono.shift)) {
vdata->monotonic_time_snsec -=
((u64)NSEC_PER_SEC) << tk->tkr_mono.shift;
vdata->monotonic_time_sec++;
}
base = &vdata->basetime[CLOCK_TAI];
base->sec = tk->xtime_sec + (s64)tk->tai_offset;
base->nsec = tk->tkr_mono.xtime_nsec;

vdata->wall_time_coarse_sec = tk->xtime_sec;
vdata->wall_time_coarse_nsec = (long)(tk->tkr_mono.xtime_nsec >>
tk->tkr_mono.shift);
base = &vdata->basetime[CLOCK_MONOTONIC];
base->sec = tk->xtime_sec + tk->wall_to_monotonic.tv_sec;
nsec = tk->tkr_mono.xtime_nsec;
nsec += ((u64)tk->wall_to_monotonic.tv_nsec << tk->tkr_mono.shift);
while (nsec >= (((u64)NSEC_PER_SEC) << tk->tkr_mono.shift)) {
nsec -= ((u64)NSEC_PER_SEC) << tk->tkr_mono.shift;
base->sec++;
}
base->nsec = nsec;

vdata->monotonic_time_coarse_sec =
vdata->wall_time_coarse_sec + tk->wall_to_monotonic.tv_sec;
vdata->monotonic_time_coarse_nsec =
vdata->wall_time_coarse_nsec + tk->wall_to_monotonic.tv_nsec;
base = &vdata->basetime[CLOCK_REALTIME_COARSE];
base->sec = tk->xtime_sec;
base->nsec = tk->tkr_mono.xtime_nsec >> tk->tkr_mono.shift;

while (vdata->monotonic_time_coarse_nsec >= NSEC_PER_SEC) {
vdata->monotonic_time_coarse_nsec -= NSEC_PER_SEC;
vdata->monotonic_time_coarse_sec++;
base = &vdata->basetime[CLOCK_MONOTONIC_COARSE];
base->sec = tk->xtime_sec + tk->wall_to_monotonic.tv_sec;
nsec = tk->tkr_mono.xtime_nsec >> tk->tkr_mono.shift;
nsec += tk->wall_to_monotonic.tv_nsec;
while (nsec >= NSEC_PER_SEC) {
nsec -= NSEC_PER_SEC;
base->sec++;
}
base->nsec = nsec;

gtod_write_end(vdata);
}
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