[PATCH v3 0/12] arm+arm64: vdso unification to lib/vdso/

[Mark Salyzyn <salyzyn@android.com>]

Take an effort to recode the arm64 vdso code from assembler to C
previously submitted by Andrew Pinski <apinski@cavium.com>, rework
it for use in both arm and arm64, overlapping any optimizations
for each architecture. But instead of landing it in arm64, land the
result into lib/vdso and unify both implementations to simplify
future maintenance. This will act as the basis for implementing
arm64 vdso32 in the future.


apinski@cavium.com made the following claims in the original patch:

This allows the compiler to optimize the divide by 1000 and remove
the other divides.

On ThunderX, gettimeofday improves by 32%.  On ThunderX 2,
gettimeofday improves by 18%.

Note I noticed a bug in the old implementation of __kernel_clock_getres;
it was checking only the lower 32bits of the pointer; this would work
for most cases but could fail in a few.


Signed-off-by: Mark Salyzyn <salyzyn@android.com>
Cc: James Morse <james.morse@arm.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Dmitry Safonov <dsafonov@virtuozzo.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Laura Abbott <labbott@redhat.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Andy Gross <andy.gross@linaro.org>
Cc: Kevin Brodsky <kevin.brodsky@arm.com>
Cc: Andrew Pinski <apinski@cavium.com>
Cc: linux-kernel@vger.kernel.org
Cc: linux-arm-kernel@lists.infradead.org

v2:
- split first CL into 7 pieces, there were cosmetic adjustments.
- make sure profiling is turned off.
- kept quiet_cmd_vdsoas.

v3:
- changed are a result of private email review comments
- rebase
- move arch/arm/vdso/vgettimeofday.c to lib/vdso/vgettimeofday.c
- adjust vgettimeofday.c to be a better global candidate, switch to using
  ARCH_PROVIDES_TIMER and __arch_counter_get() as more generic.
- do not expose gettimeofday if arch does not support user space timer