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linux/lib/vdso/Kconfig

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lib/vdso: Provide generic VDSO implementation In the last few years the kernel gained quite some architecture specific vdso implementations which contain very similar code. Introduce a generic VDSO implementation of gettimeofday() which will be shareable between architectures once they are converted over. The implementation is based on the current x86 VDSO code. [ tglx: Massaged changelog and made the kernel doc tabular ] Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Tested-by: Shijith Thotton <sthotton@marvell.com> Tested-by: Andre Przywara <andre.przywara@arm.com> Cc: linux-arch@vger.kernel.org Cc: linux-arm-kernel@lists.infradead.org Cc: linux-mips@vger.kernel.org Cc: linux-kselftest@vger.kernel.org Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Will Deacon <will.deacon@arm.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Russell King <linux@armlinux.org.uk> Cc: Ralf Baechle <ralf@linux-mips.org> Cc: Paul Burton <paul.burton@mips.com> Cc: Daniel Lezcano <daniel.lezcano@linaro.org> Cc: Mark Salyzyn <salyzyn@android.com> Cc: Peter Collingbourne <pcc@google.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Dmitry Safonov <0x7f454c46@gmail.com> Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk> Cc: Huw Davies <huw@codeweavers.com> Link: https://lkml.kernel.org/r/20190621095252.32307-3-vincenzo.frascino@arm.com
2019-06-21 12:52:29 +03:00
# SPDX-License-Identifier: GPL-2.0
config HAVE_GENERIC_VDSO
bool
if HAVE_GENERIC_VDSO
config GENERIC_GETTIMEOFDAY
bool
help
This is a generic implementation of gettimeofday vdso.
Each architecture that enables this feature has to
provide the fallback implementation.
config GENERIC_VDSO_32
bool
depends on GENERIC_GETTIMEOFDAY && !64BIT
help
This config option helps to avoid possible performance issues
in 32 bit only architectures.
config GENERIC_COMPAT_VDSO
bool
help
This config option enables the compat VDSO layer.
lib/vdso: Prepare for time namespace support To support time namespaces in the vdso with a minimal impact on regular non time namespace affected tasks, the namespace handling needs to be hidden in a slow path. The most obvious place is vdso_seq_begin(). If a task belongs to a time namespace then the VVAR page which contains the system wide vdso data is replaced with a namespace specific page which has the same layout as the VVAR page. That page has vdso_data->seq set to 1 to enforce the slow path and vdso_data->clock_mode set to VCLOCK_TIMENS to enforce the time namespace handling path. The extra check in the case that vdso_data->seq is odd, e.g. a concurrent update of the vdso data is in progress, is not really affecting regular tasks which are not part of a time namespace as the task is spin waiting for the update to finish and vdso_data->seq to become even again. If a time namespace task hits that code path, it invokes the corresponding time getter function which retrieves the real VVAR page, reads host time and then adds the offset for the requested clock which is stored in the special VVAR page. If VDSO time namespace support is disabled the whole magic is compiled out. Initial testing shows that the disabled case is almost identical to the host case which does not take the slow timens path. With the special timens page installed the performance hit is constant time and in the range of 5-7%. For the vdso functions which are not using the sequence count an unconditional check for vdso_data->clock_mode is added which switches to the real vdso when the clock_mode is VCLOCK_TIMENS. [avagin: Make do_hres_timens() work with raw clocks too: choose vdso_data pointer by CS_RAW offset.] Suggested-by: Andy Lutomirski <luto@kernel.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Andrei Vagin <avagin@gmail.com> Signed-off-by: Dmitry Safonov <dima@arista.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Link: https://lore.kernel.org/r/20191112012724.250792-21-dima@arista.com
2019-11-12 04:27:09 +03:00
config GENERIC_VDSO_TIME_NS
bool
help
Selected by architectures which support time namespaces in the
VDSO
lib/vdso: Provide generic VDSO implementation In the last few years the kernel gained quite some architecture specific vdso implementations which contain very similar code. Introduce a generic VDSO implementation of gettimeofday() which will be shareable between architectures once they are converted over. The implementation is based on the current x86 VDSO code. [ tglx: Massaged changelog and made the kernel doc tabular ] Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Tested-by: Shijith Thotton <sthotton@marvell.com> Tested-by: Andre Przywara <andre.przywara@arm.com> Cc: linux-arch@vger.kernel.org Cc: linux-arm-kernel@lists.infradead.org Cc: linux-mips@vger.kernel.org Cc: linux-kselftest@vger.kernel.org Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Will Deacon <will.deacon@arm.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Russell King <linux@armlinux.org.uk> Cc: Ralf Baechle <ralf@linux-mips.org> Cc: Paul Burton <paul.burton@mips.com> Cc: Daniel Lezcano <daniel.lezcano@linaro.org> Cc: Mark Salyzyn <salyzyn@android.com> Cc: Peter Collingbourne <pcc@google.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Dmitry Safonov <0x7f454c46@gmail.com> Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk> Cc: Huw Davies <huw@codeweavers.com> Link: https://lkml.kernel.org/r/20190621095252.32307-3-vincenzo.frascino@arm.com
2019-06-21 12:52:29 +03:00
endif
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