x86-64: Add time to vDSO

The only fast implementation of time(2) we expose is through the
vsyscall page and we want to get userspace to stop using the
vsyscall page.  So make it available through the vDSO as well.

This is essentially a cut-n-paste job.

Signed-off-by: Andy Lutomirski <luto@mit.edu>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Borislav Petkov <bp@amd64.org>
Link: http://lkml.kernel.org/r/%3Cbf963bac5207de4b29613f27c42705e4371812a8.1306156808.git.luto%40mit.edu%3E
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

diff --git a/arch/x86/vdso/vclock_gettime.c b/arch/x86/vdso/vclock_gettime.c
index 28b2c00bd1be82148ab677ca68baf77c381a1871..e6e9f90a8cd7c5fb5cb1f161b08bf8946a8116ae 100644 (file)
--- a/arch/x86/vdso/vclock_gettime.c
+++ b/arch/x86/vdso/vclock_gettime.c
@@ -2,7 +2,7 @@
  * Copyright 2006 Andi Kleen, SUSE Labs.
  * Subject to the GNU Public License, v.2
  *
- * Fast user context implementation of clock_gettime and gettimeofday.
+ * Fast user context implementation of clock_gettime, gettimeofday, and time.
  *
  * The code should have no internal unresolved relocations.
  * Check with readelf after changing.
@@ -160,3 +160,36 @@ 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;
+}
+
+notrace time_t __vdso_time(time_t *t)
+{
+       unsigned seq;
+       time_t result;
+       if (unlikely(!VVAR(vsyscall_gtod_data).sysctl_enabled))
+               return time_syscall(t);
+
+       do {
+               seq = read_seqbegin(&VVAR(vsyscall_gtod_data).lock);
+
+               result = VVAR(vsyscall_gtod_data).wall_time_sec;
+
+       } while (read_seqretry(&VVAR(vsyscall_gtod_data).lock, seq));
+
+       if (t)
+               *t = result;
+       return result;
+}
+int time(time_t *t)
+       __attribute__((weak, alias("__vdso_time")));

diff --git a/arch/x86/vdso/vdso.lds.S b/arch/x86/vdso/vdso.lds.S
index 81f250011f7153ea0a7df4bec68da3fa9f1b735a..b96b2677cad82820207bb38a3e09bdd8c4a61eba 100644 (file)
--- a/arch/x86/vdso/vdso.lds.S
+++ b/arch/x86/vdso/vdso.lds.S
@@ -23,6 +23,8 @@ VERSION {
                __vdso_gettimeofday;
                getcpu;
                __vdso_getcpu;
+               time;
+               __vdso_time;
        local: *;
        };
 }