1 files changed, 65 insertions, 38 deletions

diff --git a/arch/x86/vdso/vclock_gettime.c b/arch/x86/vdso/vclock_gettime.c
index a724905fdae7..6bc0e723b6e8 100644
--- a/arch/x86/vdso/vclock_gettime.c
+++ b/arch/x86/vdso/vclock_gettime.c
@@ -6,7 +6,6 @@
  *
  * The code should have no internal unresolved relocations.
  * Check with readelf after changing.
- * Also alternative() doesn't work.
  */
 
 /* Disable profiling for userspace code: */
@@ -17,6 +16,7 @@
 #include <linux/time.h>
 #include <linux/string.h>
 #include <asm/vsyscall.h>
+#include <asm/fixmap.h>
 #include <asm/vgtod.h>
 #include <asm/timex.h>
 #include <asm/hpet.h>
@@ -25,6 +25,43 @@
 
 #define gtod (&VVAR(vsyscall_gtod_data))
 
+notrace static cycle_t vread_tsc(void)
+{
+	cycle_t ret;
+	u64 last;
+
+	/*
+	 * Empirically, a fence (of type that depends on the CPU)
+	 * before rdtsc is enough to ensure that rdtsc is ordered
+	 * with respect to loads.  The various CPU manuals are unclear
+	 * as to whether rdtsc can be reordered with later loads,
+	 * but no one has ever seen it happen.
+	 */
+	rdtsc_barrier();
+	ret = (cycle_t)vget_cycles();
+
+	last = VVAR(vsyscall_gtod_data).clock.cycle_last;
+
+	if (likely(ret >= last))
+		return ret;
+
+	/*
+	 * GCC likes to generate cmov here, but this branch is extremely
+	 * predictable (it's just a funciton 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;
+}
+
+static notrace cycle_t vread_hpet(void)
+{
+	return readl((const void __iomem *)fix_to_virt(VSYSCALL_HPET) + 0xf0);
+}
+
 notrace static long vdso_fallback_gettime(long clock, struct timespec *ts)
 {
 	long ret;
@@ -36,9 +73,12 @@ notrace static long vdso_fallback_gettime(long clock, struct timespec *ts)
 notrace static inline long vgetns(void)
 {
 	long v;
-	cycles_t (*vread)(void);
-	vread = gtod->clock.vread;
-	v = (vread() - gtod->clock.cycle_last) & gtod->clock.mask;
+	cycles_t cycles;
+	if (gtod->clock.vclock_mode == VCLOCK_TSC)
+		cycles = vread_tsc();
+	else
+		cycles = vread_hpet();
+	v = (cycles - gtod->clock.cycle_last) & gtod->clock.mask;
 	return (v * gtod->clock.mult) >> gtod->clock.shift;
 }
 
@@ -116,21 +156,21 @@ notrace static noinline int do_monotonic_coarse(struct timespec *ts)
 
 notrace int __vdso_clock_gettime(clockid_t clock, struct timespec *ts)
 {
-	if (likely(gtod->sysctl_enabled))
-		switch (clock) {
-		case CLOCK_REALTIME:
-			if (likely(gtod->clock.vread))
-				return do_realtime(ts);
-			break;
-		case CLOCK_MONOTONIC:
-			if (likely(gtod->clock.vread))
-				return do_monotonic(ts);
-			break;
-		case CLOCK_REALTIME_COARSE:
-			return do_realtime_coarse(ts);
-		case CLOCK_MONOTONIC_COARSE:
-			return do_monotonic_coarse(ts);
-		}
+	switch (clock) {
+	case CLOCK_REALTIME:
+		if (likely(gtod->clock.vclock_mode != VCLOCK_NONE))
+			return do_realtime(ts);
+		break;
+	case CLOCK_MONOTONIC:
+		if (likely(gtod->clock.vclock_mode != VCLOCK_NONE))
+			return do_monotonic(ts);
+		break;
+	case CLOCK_REALTIME_COARSE:
+		return do_realtime_coarse(ts);
+	case CLOCK_MONOTONIC_COARSE:
+		return do_monotonic_coarse(ts);
+	}
+
 	return vdso_fallback_gettime(clock, ts);
 }
 int clock_gettime(clockid_t, struct timespec *)
@@ -139,7 +179,7 @@ int clock_gettime(clockid_t, struct timespec *)
 notrace int __vdso_gettimeofday(struct timeval *tv, struct timezone *tz)
 {
 	long ret;
-	if (likely(gtod->sysctl_enabled && gtod->clock.vread)) {
+	if (likely(gtod->clock.vclock_mode != VCLOCK_NONE)) {
 		if (likely(tv != NULL)) {
 			BUILD_BUG_ON(offsetof(struct timeval, tv_usec) !=
 				     offsetof(struct timespec, tv_nsec) ||
@@ -161,27 +201,14 @@ notrace int __vdso_gettimeofday(struct timeval *tv, struct timezone *tz)
 int gettimeofday(struct timeval *, struct timezone *)
 	__attribute__((weak, alias("__vdso_gettimeofday")));
 
-/* This will break when the xtime seconds get inaccurate, but that is
- * unlikely */
-
-static __always_inline long time_syscall(long *t)
-{
-	long secs;
-	asm volatile("syscall"
-		     : "=a" (secs)
-		     : "0" (__NR_time), "D" (t) : "cc", "r11", "cx", "memory");
-	return secs;
-}
-
+/*
+ * This will break when the xtime seconds get inaccurate, but that is
+ * unlikely
+ */
 notrace time_t __vdso_time(time_t *t)
 {
-	time_t result;
-
-	if (unlikely(!VVAR(vsyscall_gtod_data).sysctl_enabled))
-		return time_syscall(t);
-
 	/* This is atomic on x86_64 so we don't need any locks. */
-	result = ACCESS_ONCE(VVAR(vsyscall_gtod_data).wall_time_sec);
+	time_t result = ACCESS_ONCE(VVAR(vsyscall_gtod_data).wall_time_sec);
 
 	if (t)
 		*t = result;