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Subject[RFC 15/20] timens: Optimize zero-offsets
Date
Fall through on host or in ns without time set.
Add TIMENS_FALLBACK_SYSCALL which might be wired up if timens offsets
should be unknown for userspace (will result in fall-back to syscalls).

Signed-off-by: Dmitry Safonov <dima@arista.com>
---
arch/x86/entry/vdso/vclock_gettime.c | 17 +++++++++++++----
include/linux/timens_offsets.h | 12 ++++++++++--
kernel/time/posix-timers.c | 21 ++++++++++++---------
kernel/time_namespace.c | 2 +-
4 files changed, 36 insertions(+), 16 deletions(-)

diff --git a/arch/x86/entry/vdso/vclock_gettime.c b/arch/x86/entry/vdso/vclock_gettime.c
index a265e2737a9a..458cb1992e2e 100644
--- a/arch/x86/entry/vdso/vclock_gettime.c
+++ b/arch/x86/entry/vdso/vclock_gettime.c
@@ -252,17 +252,25 @@ notrace void set_normalized_timespec(struct timespec *ts, time_t sec, s64 nsec)
ts->tv_nsec = nsec;
}

-notrace static __always_inline void monotonic_to_ns(struct timespec *ts)
+notrace static __always_inline int monotonic_to_ns(struct timespec *ts)
{
#ifdef CONFIG_TIME_NS
struct timens_offsets *timens = (struct timens_offsets *) &timens_page;
struct timespec offset;

+ /* Optimization: time is the same as on host, return right away */
+ if (!(timens->flags & TIMENS_USE_OFFSETS))
+ return 0;
+
+ if (timens->flags & TIMENS_FALLBACK_SYSCALL)
+ return -1;
+
offset = timespec64_to_timespec(timens->monotonic_time_offset);

*ts = timespec_add(*ts, offset);

#endif
+ return 0;
}

notrace static int __always_inline do_monotonic(struct timespec *ts)
@@ -283,8 +291,6 @@ notrace static int __always_inline do_monotonic(struct timespec *ts)
ts->tv_sec += __iter_div_u64_rem(ns, NSEC_PER_SEC, &ns);
ts->tv_nsec = ns;

- monotonic_to_ns(ts);
-
return mode;
}

@@ -306,7 +312,6 @@ notrace static void do_monotonic_coarse(struct timespec *ts)
ts->tv_sec = gtod->monotonic_time_coarse_sec;
ts->tv_nsec = gtod->monotonic_time_coarse_nsec;
} while (unlikely(gtod_read_retry(gtod, seq)));
- monotonic_to_ns(ts);
}

notrace int __vdso_clock_gettime(clockid_t clock, struct timespec *ts)
@@ -319,12 +324,16 @@ notrace int __vdso_clock_gettime(clockid_t clock, struct timespec *ts)
case CLOCK_MONOTONIC:
if (do_monotonic(ts) == VCLOCK_NONE)
goto fallback;
+ if (monotonic_to_ns(ts))
+ goto fallback;
break;
case CLOCK_REALTIME_COARSE:
do_realtime_coarse(ts);
break;
case CLOCK_MONOTONIC_COARSE:
do_monotonic_coarse(ts);
+ if (monotonic_to_ns(ts))
+ goto fallback;
break;
default:
goto fallback;
diff --git a/include/linux/timens_offsets.h b/include/linux/timens_offsets.h
index 92a8ea5601eb..8c43e7c3e632 100644
--- a/include/linux/timens_offsets.h
+++ b/include/linux/timens_offsets.h
@@ -2,6 +2,13 @@
#ifndef _LINUX_TIME_OFFSETS_H
#define _LINUX_TIME_OFFSETS_H

+enum {
+ /* We're in namespace - add offsets from vvar */
+ TIMENS_USE_OFFSETS = 1,
+ /* Don't expose host's offsets, fall back to syscall - slow */
+ TIMENS_FALLBACK_SYSCALL = 2, /* TODO if anyone actually interested */
+};
+
/*
* Time offsets need align as they're placed on vvar page,
* which should have tail paddings on ia32 vdso.
@@ -10,8 +17,9 @@
* to timespec because of a padding occuring between the fields.
*/
struct timens_offsets {
- struct timespec64 monotonic_time_offset __aligned(8);
- struct timespec64 monotonic_boottime_offset __aligned(8);
+ u64 flags;
+ struct timespec64 monotonic_time_offset __aligned(8);
+ struct timespec64 monotonic_boottime_offset __aligned(8);
};

#endif
diff --git a/kernel/time/posix-timers.c b/kernel/time/posix-timers.c
index 701cb0602b7a..576dbd24c498 100644
--- a/kernel/time/posix-timers.c
+++ b/kernel/time/posix-timers.c
@@ -210,7 +210,7 @@ static void common_timens_adjust(clockid_t which_clock, struct timespec64 *tp)
{
struct timens_offsets *ns_offsets = current->nsproxy->time_ns->offsets;

- if (!ns_offsets)
+ if (!ns_offsets || !(ns_offsets->flags & TIMENS_USE_OFFSETS))
return;

switch (which_clock) {
@@ -234,15 +234,16 @@ static int posix_ktime_set_ts(clockid_t which_clock,
struct timens_offsets *ns_offsets = current->nsproxy->time_ns->offsets;
struct timespec64 ktp;

+ if (!ns_offsets)
+ return -EINVAL;
+
if (!ns_capable(current->nsproxy->time_ns->user_ns, CAP_SYS_TIME))
return -EPERM;

ktime_get_ts64(&ktp);

- if (ns_offsets)
- ns_offsets->monotonic_time_offset = timespec64_sub(*tp, ktp);
- else
- return -EINVAL;
+ ns_offsets->monotonic_time_offset = timespec64_sub(*tp, ktp);
+ ns_offsets->flags |= TIMENS_USE_OFFSETS;

return 0;
}
@@ -296,15 +297,17 @@ static int posix_set_boottime(clockid_t which_clock, const struct timespec64 *tp
struct timens_offsets *ns_offsets = current->nsproxy->time_ns->offsets;
struct timespec64 ktp;

+ if (!ns_offsets)
+ return -EINVAL;
+
if (!ns_capable(current->nsproxy->time_ns->user_ns, CAP_SYS_TIME))
return -EPERM;

ktime_get_boottime_ts64(&ktp);

- if (ns_offsets)
- ns_offsets->monotonic_boottime_offset = timespec64_sub(*tp, ktp);
- else
- return -EINVAL;
+ ns_offsets->monotonic_boottime_offset = timespec64_sub(*tp, ktp);
+ ns_offsets->flags |= TIMENS_USE_OFFSETS;
+
return 0;
}

diff --git a/kernel/time_namespace.c b/kernel/time_namespace.c
index f88ae0e17d92..4052bdcec110 100644
--- a/kernel/time_namespace.c
+++ b/kernel/time_namespace.c
@@ -171,7 +171,7 @@ static void clock_timens_fixup(int clockid, struct timespec64 *val, bool to_ns)
struct timens_offsets *ns_offsets = current->nsproxy->time_ns->offsets;
struct timespec64 *offsets = NULL;

- if (!ns_offsets)
+ if (!ns_offsets || !(ns_offsets->flags & TIMENS_USE_OFFSETS))
return;

if (val->tv_sec == 0 && val->tv_nsec == 0)
--
2.13.6
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