x86-64: Remove kernel.vsyscall64 sysctl

It's unnecessary overhead in code that's supposed to be highly
optimized.  Removing it allows us to remove one of the two
syscall instructions in the vsyscall page.

The only sensible use for it is for UML users, and it doesn't
fully address inconsistent vsyscall results on UML.  The real
fix for UML is to stop using vsyscalls entirely.

Signed-off-by: Andy Lutomirski <luto@mit.edu>
Cc: Jesper Juhl <jj@chaosbits.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Arjan van de Ven <arjan@infradead.org>
Cc: Jan Beulich <JBeulich@novell.com>
Cc: richard -rw- weinberger <richard.weinberger@gmail.com>
Cc: Mikael Pettersson <mikpe@it.uu.se>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Louis Rilling <Louis.Rilling@kerlabs.com>
Cc: Valdis.Kletnieks@vt.edu
Cc: pageexec@freemail.hu
Link: http://lkml.kernel.org/r/973ae803fe76f712da4b2740e66dccf452d3b1e4.1307292171.git.luto@mit.edu
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 21 insertions, 34 deletions

diff --git a/arch/x86/vdso/vclock_gettime.c b/arch/x86/vdso/vclock_gettime.c
index a724905fdae7..cf54813ac527 100644
--- a/arch/x86/vdso/vclock_gettime.c
+++ b/arch/x86/vdso/vclock_gettime.c
@@ -116,21 +116,21 @@ 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.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);
+        }
+
         return vdso_fallback_gettime(clock, ts);
 }
 int clock_gettime(clockid_t, struct timespec *)
@@ -139,7 +139,7 @@ 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.vread)) {
                 if (likely(tv != NULL)) {
                         BUILD_BUG_ON(offsetof(struct timeval, tv_usec) !=
                                      offsetof(struct timespec, tv_nsec) ||
@@ -161,27 +161,14 @@ 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;