Discussions around time namespace are there for a long time. The first attempt to implement it was in 2006 by Jeff Dike. From that time, the topic appears on and off in various discussions. There are two main use cases for time namespaces: 1. change date and time inside a container; 2. adjust clocks for a container restored from a checkpoint. “It seems like this might be one of the last major obstacles keeping migration from being used in production systems, given that not all containers and connections can be migrated as long as a time dependency is capable of messing it up.” (by github.com/dav-ell) The kernel provides access to several clocks: CLOCK_REALTIME, CLOCK_MONOTONIC, CLOCK_BOOTTIME. Last two clocks are monotonous, but the start points for them are not defined and are different for each system. When a container is migrated from one node to another, all clocks have to be restored into consistent states; in other words, they have to continue running from the same points where they have been dumped. The main idea of this patch set is adding per-namespace offsets for system clocks. When a process in a non-root time namespace requests time of a clock, a namespace offset is added to the current value of this clock and the sum is returned. All offsets are placed on a separate page, this allows us to map it as part of VVAR into user processes and use offsets from VDSO calls. Now offsets are implemented for CLOCK_MONOTONIC and CLOCK_BOOTTIME clocks. v5..v6 Changes: * Used current_is_single_threaded() instead of thread_group_empty() (Thanks for the review, Andy). * Changed errno code when there are threads on timens joining to something more grepabble (EUSERS). * posix_get_timespec() should have been posix_get_monotonic_timespec() (Thanks, Thomas) * timens_add_monotonic() & timens_add_boottime() were relocated to the patch that introduces (struct timens_offsets) (Thomas) * Avoid breaking alarmtimer for ALARM_REALTIME (Thanks, Thomas) * Nested namespace inherits father's offsets now (Andrei while working on CRIU side for time namespace) * A minor conflict with commit dbc1625fc9de ("hrtimer: Consolidate hrtimer_init() + hrtimer_init_sleeper() calls") in linux-next [Sending against next-20190814] [v1..v5 Changelogs is at the very bottom here] Our performance measurements show that the price of VDSO's clock_gettime() in a child time namespace is about 8% with a hot CPU cache and about 90% with a cold CPU cache. There is no performance regression for host processes outside time namespace on those tests. We wrote two small benchmarks. The first one gettime_perf.c calls clock_gettime() in a loop for 3 seconds. It shows us performance with a hot CPU cache (more clock_gettime() cycles - the better): | before | CONFIG_TIME_NS=n | host | inside timens -------------------------------------------------------------- | 161822960 | 161147792 | 160187142 | 150584782 | 161891728 | 161489804 | 159914989 | 150417019 | 161891770 | 161098734 | 160123179 | 150601277 | 161687686 | 161114738 | 159874249 | 150243276 | 161247151 | 161411636 | 159096392 | 149637536 -------------------------------------------------------------- avg | 161708259 | 161252540 | 159839190 | 150296778 diff % | 100 | 99.7 | 98.8 | 92.9 ------------------------------------------------------------- stdev % | 0.2 | 0.1 | 0.1 | 0.2 The gettime_perf_cold test does 10K iterations. In each iteration, it drops cpu caches for vdso pages, clflush is used for this, then it runs rdtsc(); clock_gettime; rdtsc(); and prints the number of tsc cycles. (lesser tsc per cycle - the better): | before | CONFIG_TIME_NS=n | host | inside timens -------------------------------------------------------------- tsc | 434 | 433 | 437 | 477 stdev(tsc) | 5 | 5 | 5 | 3 diff (%) | 1 | 1 | 100.1 | 109 vdsotest results: https://gist.github.com/avagin/f290afb8b721ae0522a561d585f34de0 The numbers gathered on Intel(R) Core(TM) i5-6300U CPU @ 2.40GHz. Cc: Adrian Reber <adrian@xxxxxxxx> Cc: Andrei Vagin <avagin@xxxxxxxxxx> Cc: Andy Lutomirski <luto@xxxxxxxxxx> Cc: Arnd Bergmann <arnd@xxxxxxxx> Cc: Christian Brauner <christian.brauner@xxxxxxxxxx> Cc: Cyrill Gorcunov <gorcunov@xxxxxxxxxx> Cc: Dmitry Safonov <0x7f454c46@xxxxxxxxx> Cc: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx> Cc: Ingo Molnar <mingo@xxxxxxxxxx> Cc: Jann Horn <jannh@xxxxxxxxxx> Cc: Jeff Dike <jdike@xxxxxxxxxxx> Cc: Oleg Nesterov <oleg@xxxxxxxxxx> Cc: Pavel Emelyanov <xemul@xxxxxxxxxxxxx> Cc: Shuah Khan <shuah@xxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: Vincenzo Frascino <vincenzo.frascino@xxxxxxx> Cc: containers@xxxxxxxxxxxxxxxxxxxxxxxxxx Cc: criu@xxxxxxxxxx Cc: linux-api@xxxxxxxxxxxxxxx Cc: x86@xxxxxxxxxx v6 on github (if someone prefers `git pull` or `git log`): https://github.com/0x7f454c46/linux/tree/timens-v6 v5: https://lkml.kernel.org/r/20190729215758.28405-1-dima@xxxxxxxxxx v4: https://lkml.kernel.org/r/20190612192628.23797-1-dima@xxxxxxxxxx v3: https://lkml.kernel.org/r/20190425161416.26600-1-dima@xxxxxxxxxx v2: https://lore.kernel.org/lkml/20190206001107.16488-1-dima@xxxxxxxxxx/ RFC: https://lkml.kernel.org/r/20180919205037.9574-1-dima@xxxxxxxxxx/ v4..v5 Changes: * Rebased over generic vdso (already in master) * Addressing review comments by Thomas Gleixner (thanks much for your time and patience): - Dropping `timens` prefix from subjects (it's not a subsystem) - Keeping commit messages in a neutral technical form - Splitting unreasonably large patches - Document code with missing comments - Dropped dead code that's not compiled with !CONFIG_TIME_NS * Updated performance results [here, at the bottom] * Split vdso jump tables patch * Allow unshare() with many threads: it's safe until fork()/clone(), where we check for CLONE_THREADS * Add missed check in setns() for CLONE_VM | CLONE_THREADS * Fixed compilation with !CONFIG_UTS_NS * Add a plan in selftests (prevents new warning "Planned tests != run tests") * Set jump table section address & size to (-1UL) just in case if there is no such section while running vdso2c (and WARN() on boot in such case) v3..v4 Changes: * CLOCKE_NEWTIME is unshare()-only flag now (CLON_PIDFD took previous value) * Addressing Jann Horn's feedback - we don't allow CLONE_THREAD or CLONE_VM together with CLONE_NEWTIME (thanks for spotting!) * Addressing issues found by Thomas - removed unmaintainable CLOCK_TIMENS and introduced another call back into k_clock to get ktime instead of getting timespec and converting it (Patch 03) * Renaming timens_offsets members to omit _offset postfix (thanks Cyrill for the suggestion) * Suggestions, renaming and making code more maintainable from Thomas's feedback (thanks much!) * Fixing out-of-bounds and other issues in procfs file (kudos Jann Horn) * vdso_fault() can be called on a remote task by /proc/$pid/mem or process_vm_readv() - addressed by adding a slow-path with searching for owner's namespace (thanks for spotting this unobvious issue, Jann) * Other nits by Jann Horn v2..v3: Major changes: * Simplify two VDSO images by using static_branch() in vclock_gettime() Removes unwanted conflicts with generic VDSO movement patches and simplifies things by dropping too invasive linker magic. As an alternative to static_branch() we tested an attempt to introduce home-made dynamic patching called retcalls: https://github.com/0x7f454c46/linux/commit/4cc0180f6d65 Considering some theoretical problems with toolchains, we decided to go with long well-tested nop-patching in static_branch(). Though, it was needed to provide backend for relative code. * address Thomas' comments. * add sanity checks for offsets: - the current clock time in a namespace has to be in [0, KTIME_MAX / 2). KTIME_MAX is divided by two here to be sure that the KTIME_MAX limit is still unreachable. Link: https://lkml.org/lkml/2018/9/19/950 Link: https://lkml.org/lkml/2019/2/5/867 v1..v2: There are two major changes: * Two versions of the VDSO library to avoid a performance penalty for host tasks outside time namespace (as suggested by Andy and Thomas). As it has been discussed on timens RFC, adding a new conditional branch `if (inside_time_ns)` on VDSO for all processes is undesirable. It will add a penalty for everybody as branch predictor may mispredict the jump. Also there are instruction cache lines wasted on cmp/jmp. Those effects of introducing time namespace are very much unwanted having in mind how much work have been spent on micro-optimisation VDSO code. Addressing those problems, there are two versions of VDSO's .so: for host tasks (without any penalty) and for processes inside of time namespace with clk_to_ns() that subtracts offsets from host's time. * Allow to set clock offsets for a namespace only before any processes appear in it. Now a time namespace looks similar to a pid namespace in a way how it is created: unshare(CLONE_NEWTIME) system call creates a new time namespace, but doesn't set it to the current process. Then all children of the process will be born in the new time namespace, or a process can use the setns() system call to join a namespace. This scheme allows to create a new time namespaces, set clock offsets and then populate the namespace with processes. Andrei Vagin (24): ns: Introduce Time Namespace timens: Add timens_offsets posix-clocks: Rename the clock_get() into clock_get_timespec() posix-clocks: Rename .clock_get_timespec() callbacks accordingly alarmtimer: Rename gettime() callback to get_ktime() alarmtimer: Provide get_timespec() callback posix-clocks: Introduce clock_get_ktime() callback posix-timers: Use clock_get_ktime() in common_timer_get() posix-clocks: Wire up clock_gettime() with timens offsets kernel: Add do_timens_ktime_to_host() helper timerfd: Make timerfd_settime() time namespace aware posix-timers: Make timer_settime() time namespace aware alarmtimer: Make nanosleep time namespace aware hrtimers: Prepare hrtimer_nanosleep() for time namespaces posix-timers: Make clock_nanosleep() time namespace aware x86/vdso: Add offsets page in vvar vdso: Introduce vdso_static_branch_unlikely() x86/vdso: Enable static branches for the timens vdso fs/proc: Introduce /proc/pid/timens_offsets selftest/timens: Add a test for timerfd selftest/timens: Add a test for clock_nanosleep() selftest/timens: Add timer offsets test selftests/timens: Add a simple perf test for clock_gettime() selftest/timens: Check that a right vdso is mapped after fork and exec Dmitry Safonov (12): fd/proc: Respect boottime inside time namespace for /proc/uptime x86/vdso2c: Correct err messages on file opening x86/vdso2c: Convert iterator to unsigned x86/vdso/Makefile: Add vobjs32 x86/vdso: Restrict splitting VVAR VMA x86/vdso: Rename vdso_image {.data=>.text} x86/vdso: Allocate timens vdso x86/vdso: Switch image on setns()/clone() x86/vdso2c: Process jump tables posix-clocks: Add align for timens_offsets selftest/timens: Add Time Namespace test for supported clocks selftest/timens: Add procfs selftest MAINTAINERS | 3 + arch/Kconfig | 5 + arch/x86/Kconfig | 1 + arch/x86/entry/vdso/Makefile | 15 +- arch/x86/entry/vdso/vdso-layout.lds.S | 10 +- arch/x86/entry/vdso/vdso2c.c | 7 +- arch/x86/entry/vdso/vdso2c.h | 22 +- arch/x86/entry/vdso/vma.c | 177 +++++++- arch/x86/include/asm/jump_label.h | 14 + arch/x86/include/asm/vdso.h | 14 +- arch/x86/kernel/jump_label.c | 14 + fs/proc/base.c | 95 +++++ fs/proc/namespaces.c | 4 + fs/proc/uptime.c | 3 + fs/timerfd.c | 3 + include/linux/hrtimer.h | 2 +- include/linux/jump_label.h | 8 + include/linux/nsproxy.h | 2 + include/linux/posix-timers.h | 3 + include/linux/proc_ns.h | 3 + include/linux/time_namespace.h | 114 ++++++ include/linux/timens_offsets.h | 18 + include/linux/user_namespace.h | 1 + include/uapi/linux/sched.h | 6 + init/Kconfig | 9 + kernel/Makefile | 1 + kernel/fork.c | 16 +- kernel/nsproxy.c | 41 +- kernel/time/alarmtimer.c | 68 ++- kernel/time/hrtimer.c | 8 +- kernel/time/posix-clock.c | 8 +- kernel/time/posix-cpu-timers.c | 32 +- kernel/time/posix-stubs.c | 15 +- kernel/time/posix-timers.c | 88 ++-- kernel/time/posix-timers.h | 7 +- kernel/time_namespace.c | 387 ++++++++++++++++++ lib/vdso/gettimeofday.c | 53 +++ tools/testing/selftests/Makefile | 1 + tools/testing/selftests/timens/.gitignore | 8 + tools/testing/selftests/timens/Makefile | 12 + .../selftests/timens/clock_nanosleep.c | 102 +++++ tools/testing/selftests/timens/config | 1 + tools/testing/selftests/timens/exec.c | 93 +++++ tools/testing/selftests/timens/gettime_perf.c | 101 +++++ .../selftests/timens/gettime_perf_cold.c | 160 ++++++++ tools/testing/selftests/timens/log.h | 26 ++ tools/testing/selftests/timens/procfs.c | 144 +++++++ tools/testing/selftests/timens/timens.c | 185 +++++++++ tools/testing/selftests/timens/timens.h | 63 +++ tools/testing/selftests/timens/timer.c | 118 ++++++ tools/testing/selftests/timens/timerfd.c | 129 ++++++ 51 files changed, 2305 insertions(+), 115 deletions(-) create mode 100644 include/linux/time_namespace.h create mode 100644 include/linux/timens_offsets.h create mode 100644 kernel/time_namespace.c create mode 100644 tools/testing/selftests/timens/.gitignore create mode 100644 tools/testing/selftests/timens/Makefile create mode 100644 tools/testing/selftests/timens/clock_nanosleep.c create mode 100644 tools/testing/selftests/timens/config create mode 100644 tools/testing/selftests/timens/exec.c create mode 100644 tools/testing/selftests/timens/gettime_perf.c create mode 100644 tools/testing/selftests/timens/gettime_perf_cold.c create mode 100644 tools/testing/selftests/timens/log.h create mode 100644 tools/testing/selftests/timens/procfs.c create mode 100644 tools/testing/selftests/timens/timens.c create mode 100644 tools/testing/selftests/timens/timens.h create mode 100644 tools/testing/selftests/timens/timer.c create mode 100644 tools/testing/selftests/timens/timerfd.c -- 2.22.0