From: Dmitry Safonov <dima@arista.com> To: linux-kernel@vger.kernel.org Cc: Dmitry Safonov <0x7f454c46@gmail.com>, Dmitry Safonov <dima@arista.com>, Adrian Reber <adrian@lisas.de>, Andrei Vagin <avagin@openvz.org>, Andy Lutomirski <luto@kernel.org>, Arnd Bergmann <arnd@arndb.de>, Christian Brauner <christian.brauner@ubuntu.com>, Cyrill Gorcunov <gorcunov@openvz.org>, "Eric W. Biederman" <ebiederm@xmission.com>, "H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>, Jann Horn <jannh@google.com>, Jeff Dike <jdike@addtoit.com>, Oleg Nesterov <oleg@redhat.com>, Pavel Emelyanov <xemul@virtuozzo.com>, Shuah Khan <shuah@kernel.org>, Thomas Gleixner <tglx@linutronix.de>, Vincenzo Frascino <vincenzo.frascino@arm.com>, containers@lists.linux-foundation.org, criu@openvz.org, linux-api@vger.kernel.org, x86@kernel.org Subject: [PATCHv8 00/34] kernel: Introduce Time Namespace Date: Tue, 12 Nov 2019 01:26:49 +0000 Message-ID: <20191112012724.250792-1-dima@arista.com> (raw) 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. v7..v8 Changes: * Fix compile-time errors: - on architectures without the support of time namespaces. - when CONFIG_POSIX_TIMERS isn't set. * Added checks in selftests for CONFIG_POSIX_TIMERS. * Inline do_hres and do_coarse. (And added Tested-by Vincenzo - thanks!) * Make TIME_NS depends on GENERIC_VDSO_TIME_NS and set it per-arch. [v1..v7 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): The first table shows performance of clock_gettime() in the root time namespace. | before | TIME_NS=n | TIMENS=y ------------------------------------------- | 150363883 | 167076184 | 164979177 | 150616056 | 167348942 | 165202727 | 150679279 | 167235485 | 165230267 | 150622312 | 167078735 | 165284077 | 150706992 | 167301837 | 165372663 | 150563707 | 167207900 | 165395728 ------------------------------------------- avg | 150592038 | 167208180 | 165244106 diff % | 100 | 111 | 109.7 ------------------------------------------- stdev % | 0.08 | 0.07 | 0.1 We can see the 11% performance improvement when CONFIG_TIME_NS is disabled. This is achieved by adding the unlikely hint into vdso_read_begin() and inlining do_hres() and do_coarse(). When CONFIG_TIME_NS is enabled, there is one more clobbered register in the __vdso_clock_gettime function. And this fact explains the performance difference between the two right columns. The second table shows the performance of clock_gettime in a non-root time namespace. | before | host | inside timens ---------------------------------------------- | 150363883 | 164979177 | 138133479 | 150616056 | 165202727 | 139047394 | 150679279 | 165230267 | 139284611 | 150622312 | 165284077 | 139263753 | 150706992 | 165372663 | 139175419 | 150563707 | 165395728 | 139334291 ---------------------------------------------- avg | 150592038 | 165244106 | 139039824 diff % | 100 | 109.7 | 92.3 ---------------------------------------------- stdev % | 0.08 | 0.1 | 0.3 In a sub-namespace, the performance hit is 7-8%. The bigger difference between root and non-root namespaces can be explained by the fact that do_{hres,coarse}_timens are not inlined. Inlining these functions improves performance in a sub-namespace, but there will be more clobbered registers in __vdso_clock_gettime what will decrease the performance in the root namespace. 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. Cold CPU cache (lesser tsc per cycle - the better): | before | CONFIG_TIME_NS=n | host | inside timens -------------------------------------------------------------- tsc | 476 | 480 | 487 | 531 stdev(tsc) | 0.6 | 1.3 | 4.3 | 5.7 diff (%) | 100 | 100.9 | 102 | 112 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@lisas.de> Cc: Andrei Vagin <avagin@openvz.org> Cc: Andy Lutomirski <luto@kernel.org> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Christian Brauner <christian.brauner@ubuntu.com> Cc: Cyrill Gorcunov <gorcunov@openvz.org> Cc: Dmitry Safonov <0x7f454c46@gmail.com> Cc: "Eric W. Biederman" <ebiederm@xmission.com> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: Jann Horn <jannh@google.com> Cc: Jeff Dike <jdike@addtoit.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Pavel Emelyanov <xemul@virtuozzo.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Vincenzo Frascino <vincenzo.frascino@arm.com> Cc: containers@lists.linux-foundation.org Cc: criu@openvz.org Cc: linux-api@vger.kernel.org Cc: x86@kernel.org v8 on github (if someone prefers `git pull` to `git am`): https://github.com/0x7f454c46/linux/tree/timens-v8 v7: https://lkml.kernel.org/r/20191011012341.846266-1-dima@arista.com v6: https://lkml.kernel.org/r/20190815163836.2927-1-dima@arista.com v5: https://lkml.kernel.org/r/20190729215758.28405-1-dima@arista.com v4: https://lkml.kernel.org/r/20190612192628.23797-1-dima@arista.com v3: https://lkml.kernel.org/r/20190425161416.26600-1-dima@arista.com v2: https://lore.kernel.org/lkml/20190206001107.16488-1-dima@arista.com/ RFC: https://lkml.kernel.org/r/20180919205037.9574-1-dima@arista.com/ v6..v7 Changes: * Based on Andy & Thomas suggestions and the patches that Thomas kindely sent, reworked from two VDSO code images into trick with odd seq number for timens page that goes on the place of vvar page inside ns. * Moved kernel/time_namespace.c => kernel/time/namespace.c * Fixed bpf 5sec example * Added selftests outputs * By Thomas's suggestion simplified overflow check as ktime_sub(tim, offset) * Other Thomas's review notes: stylistic, simplifications and clearifications (Thanks!) * Split VDSO patches on generic/x86 parts * Fixed kernel-doc warnings * Added checks in selftests for capabilities * Fixed bisectability issues 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] 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 (23): lib/vdso: Add unlikely() hint into vdso_read_begin() lib/vdso: make do_hres and do_coarse as __always_inline ns: Introduce Time Namespace time: Add timens_offsets to be used for tasks in timens posix-clocks: Rename the clock_get() callback to 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 fs/proc: Introduce /proc/pid/timens_offsets selftests/timens: Add a test for timerfd selftests/timens: Add a test for clock_nanosleep() selftests/timens: Add timer offsets test selftests/timens: Add a simple perf test for clock_gettime() selftests/timens: Check for right timens offsets after fork and exec Dmitry Safonov (10): fs/proc: Respect boottime inside time namespace for /proc/uptime x86/vdso: Restrict splitting VVAR VMA x86/vdso: Provide vdso_data offset on vvar_page x86/vdso: Add timens page time: Allocate per-timens vvar page x86/vdso: Handle faults on timens page x86/vdso: On timens page fault prefault also VVAR page x86/vdso: Zap vvar pages on switch a time namspace selftests/timens: Add Time Namespace test for supported clocks selftests/timens: Add procfs selftest Thomas Gleixner (1): lib/vdso: Prepare for time namespace support MAINTAINERS | 2 + arch/x86/Kconfig | 1 + arch/x86/entry/vdso/vdso-layout.lds.S | 13 +- arch/x86/entry/vdso/vdso2c.c | 3 + arch/x86/entry/vdso/vma.c | 119 ++++- arch/x86/include/asm/vdso.h | 1 + arch/x86/include/asm/vdso/gettimeofday.h | 9 + arch/x86/include/asm/vvar.h | 13 +- arch/x86/kernel/vmlinux.lds.S | 4 +- 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/nsproxy.h | 2 + include/linux/proc_ns.h | 3 + include/linux/time.h | 6 + include/linux/time_namespace.h | 128 +++++ include/linux/user_namespace.h | 1 + include/uapi/linux/sched.h | 6 + include/vdso/datapage.h | 19 +- include/vdso/helpers.h | 2 +- init/Kconfig | 8 + kernel/fork.c | 16 +- kernel/nsproxy.c | 41 +- kernel/time/Makefile | 1 + kernel/time/alarmtimer.c | 73 ++- kernel/time/hrtimer.c | 8 +- kernel/time/namespace.c | 466 ++++++++++++++++++ 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 +- lib/vdso/Kconfig | 6 + lib/vdso/gettimeofday.c | 164 +++++- mm/mmap.c | 2 + tools/perf/examples/bpf/5sec.c | 6 +- tools/testing/selftests/Makefile | 1 + tools/testing/selftests/timens/.gitignore | 8 + tools/testing/selftests/timens/Makefile | 7 + .../selftests/timens/clock_nanosleep.c | 150 ++++++ tools/testing/selftests/timens/config | 1 + tools/testing/selftests/timens/exec.c | 94 ++++ tools/testing/selftests/timens/gettime_perf.c | 95 ++++ tools/testing/selftests/timens/log.h | 26 + tools/testing/selftests/timens/procfs.c | 144 ++++++ tools/testing/selftests/timens/timens.c | 190 +++++++ tools/testing/selftests/timens/timens.h | 100 ++++ tools/testing/selftests/timens/timer.c | 123 +++++ tools/testing/selftests/timens/timerfd.c | 129 +++++ 51 files changed, 2337 insertions(+), 111 deletions(-) create mode 100644 include/linux/time_namespace.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/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 -- 2.24.0

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