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Subject[PATCH v4.16-rc6 1/1] x86/vdso: VDSO should handle clock_gettime(CLOCK_MONOTONIC_RAW) without syscall
Date

This patch implements clock_gettime(CLOCK_MONOTONIC_RAW,&ts) calls entirely in the
vDSO, without calling vdso_fallback_gettime() .

It has been augmented to support compilation with or without -DRETPOLINE / $(RETPOLINE_CFLAGS) ;
when compiled with -DRETPOLINE, not all functions calls can be inlined within __vdso_clock_gettime,
and all functions invoked by __vdso_clock_gettime must have 'indirect_branch("keep")' +
'function_return("keep")' attributes to compile, otherwise thunk relocations will be generated ;
and the functions cannot all be declared '__always_inline_', otherwise a compiler -Werror
('not all __always_inline__ functions can be inlined') is generated.
Also, compared to previous version of same patch, the do_*_coarse functions are still
not inlines, and not inadvertently changed to inline.

I still think it might be better to apply H.J. Liu's patch from
https://bugzilla.kernel.org/show_bug.cgi?id=199129 to disable
-DRETPOLINE compilation for the vDSO .

---
diff --git a/arch/x86/entry/vdso/vclock_gettime.c b/arch/x86/entry/vdso/vclock_gettime.c
index f19856d..80d65d4 100644
--- a/arch/x86/entry/vdso/vclock_gettime.c
+++ b/arch/x86/entry/vdso/vclock_gettime.c
@@ -182,29 +182,62 @@ notrace static u64 vread_tsc(void)
return last;
}

-notrace static inline u64 vgetsns(int *mode)
+notrace static inline u64 vgetcycles(int *mode)
{
- u64 v;
- cycles_t cycles;
-
- if (gtod->vclock_mode == VCLOCK_TSC)
- cycles = vread_tsc();
+ switch (gtod->vclock_mode) {
+ case VCLOCK_TSC:
+ return vread_tsc();
#ifdef CONFIG_PARAVIRT_CLOCK
- else if (gtod->vclock_mode == VCLOCK_PVCLOCK)
- cycles = vread_pvclock(mode);
+ case VCLOCK_PVCLOCK:
+ return vread_pvclock(mode);
#endif
#ifdef CONFIG_HYPERV_TSCPAGE
- else if (gtod->vclock_mode == VCLOCK_HVCLOCK)
- cycles = vread_hvclock(mode);
+ case VCLOCK_HVCLOCK:
+ return vread_hvclock(mode);
#endif
- else
+ default:
+ break;
+ }
+ return 0;
+}
+
+notrace static inline u64 vgetsns(int *mode)
+{
+ u64 v;
+ cycles_t cycles = vgetcycles(mode);
+
+ if (cycles == 0)
return 0;
+
v = (cycles - gtod->cycle_last) & gtod->mask;
return v * gtod->mult;
}

+notrace static inline u64 vgetsns_raw(int *mode)
+{
+ u64 v;
+ cycles_t cycles = vgetcycles(mode);
+
+ if (cycles == 0)
+ return 0;
+
+ v = (cycles - gtod->cycle_last) & gtod->mask;
+ return v * gtod->raw_mult;
+}
+
+#ifdef RETPOLINE
+# define _NO_THUNK_RELOCS_()(indirect_branch("keep"),\
+ function_return("keep"))
+# define _RETPOLINE_FUNC_ATTR_ __attribute__(_NO_THUNK_RELOCS_())
+# define _RETPOLINE_INLINE_ inline
+#else
+# define _RETPOLINE_FUNC_ATTR_
+# define _RETPOLINE_INLINE_ __always_inline
+#endif
+
/* 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 _RETPOLINE_INLINE_ _RETPOLINE_FUNC_ATTR_
+int do_realtime(struct timespec *ts)
{
unsigned long seq;
u64 ns;
@@ -225,7 +258,8 @@ notrace static int __always_inline do_realtime(struct timespec *ts)
return mode;
}

-notrace static int __always_inline do_monotonic(struct timespec *ts)
+notrace static _RETPOLINE_INLINE_ _RETPOLINE_FUNC_ATTR_
+int do_monotonic(struct timespec *ts)
{
unsigned long seq;
u64 ns;
@@ -246,7 +280,30 @@ notrace static int __always_inline do_monotonic(struct timespec *ts)
return mode;
}

-notrace static void do_realtime_coarse(struct timespec *ts)
+notrace static _RETPOLINE_INLINE_ _RETPOLINE_FUNC_ATTR_
+int do_monotonic_raw(struct timespec *ts)
+{
+ unsigned long seq;
+ u64 ns;
+ int mode;
+
+ do {
+ seq = gtod_read_begin(gtod);
+ mode = gtod->vclock_mode;
+ ts->tv_sec = gtod->monotonic_time_raw_sec;
+ ns = gtod->monotonic_time_raw_nsec;
+ ns += vgetsns_raw(&mode);
+ ns >>= gtod->raw_shift;
+ } 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 _RETPOLINE_FUNC_ATTR_
+void do_realtime_coarse(struct timespec *ts)
{
unsigned long seq;
do {
@@ -256,7 +313,8 @@ notrace static void do_realtime_coarse(struct timespec *ts)
} while (unlikely(gtod_read_retry(gtod, seq)));
}

-notrace static void do_monotonic_coarse(struct timespec *ts)
+notrace static _RETPOLINE_FUNC_ATTR_
+void do_monotonic_coarse(struct timespec *ts)
{
unsigned long seq;
do {
@@ -266,7 +324,8 @@ notrace static void do_monotonic_coarse(struct timespec *ts)
} while (unlikely(gtod_read_retry(gtod, seq)));
}

-notrace int __vdso_clock_gettime(clockid_t clock, struct timespec *ts)
+notrace _RETPOLINE_FUNC_ATTR_
+int __vdso_clock_gettime(clockid_t clock, struct timespec *ts)
{
switch (clock) {
case CLOCK_REALTIME:
@@ -277,6 +336,10 @@ notrace int __vdso_clock_gettime(clockid_t clock, struct timespec *ts)
if (do_monotonic(ts) == VCLOCK_NONE)
goto fallback;
break;
+ case CLOCK_MONOTONIC_RAW:
+ if (do_monotonic_raw(ts) == VCLOCK_NONE)
+ goto fallback;
+ break;
case CLOCK_REALTIME_COARSE:
do_realtime_coarse(ts);
break;
diff --git a/arch/x86/entry/vsyscall/vsyscall_gtod.c b/arch/x86/entry/vsyscall/vsyscall_gtod.c
index e1216dd..c4d89b6 100644
--- a/arch/x86/entry/vsyscall/vsyscall_gtod.c
+++ b/arch/x86/entry/vsyscall/vsyscall_gtod.c
@@ -44,6 +44,8 @@ void update_vsyscall(struct timekeeper *tk)
vdata->mask = tk->tkr_mono.mask;
vdata->mult = tk->tkr_mono.mult;
vdata->shift = tk->tkr_mono.shift;
+ vdata->raw_mult = tk->tkr_raw.mult;
+ vdata->raw_shift = tk->tkr_raw.shift;

vdata->wall_time_sec = tk->xtime_sec;
vdata->wall_time_snsec = tk->tkr_mono.xtime_nsec;
@@ -74,5 +76,8 @@ void update_vsyscall(struct timekeeper *tk)
vdata->monotonic_time_coarse_sec++;
}

+ vdata->monotonic_time_raw_sec = tk->raw_sec;
+ vdata->monotonic_time_raw_nsec = tk->tkr_raw.xtime_nsec;
+
gtod_write_end(vdata);
}
diff --git a/arch/x86/include/asm/vgtod.h b/arch/x86/include/asm/vgtod.h
index fb856c9..ec1a37c 100644
--- a/arch/x86/include/asm/vgtod.h
+++ b/arch/x86/include/asm/vgtod.h
@@ -22,7 +22,8 @@ struct vsyscall_gtod_data {
u64 mask;
u32 mult;
u32 shift;
-
+ u32 raw_mult;
+ u32 raw_shift;
/* open coded 'struct timespec' */
u64 wall_time_snsec;
gtod_long_t wall_time_sec;
@@ -32,6 +33,8 @@ struct vsyscall_gtod_data {
gtod_long_t wall_time_coarse_nsec;
gtod_long_t monotonic_time_coarse_sec;
gtod_long_t monotonic_time_coarse_nsec;
+ gtod_long_t monotonic_time_raw_sec;
+ gtod_long_t monotonic_time_raw_nsec;

int tz_minuteswest;
int tz_dsttime;
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