From: Ryan Houdek <Houdek.Ryan@fex-emu.org>

arm64: Implement userspace syscall dispatch

The first patch moves the userspace dispatch code from the common
syscall entry path. This is necessary since arm64 doesn't support
the common syscall entry path.

The second patch exposes where the sigreturn landing pad location is.
The syscall user dispatch code checks this landing pad to see if
it should skip invoking the userspace dispatch path.

The third patch is where the userspace dispatcher work is hooked up
to arm64 syscall dispatcher. Fairly straight forward, adds a new check
to the trace enter and exit paths for user dispatch.

The fourth patch just updates the selftests to handle aarch64.

The sud_bench application shows a consistent 2.3% overhead on my device
when testing. Going from 477ns to 488ns per syscall.

Ryan Houdek (4):
  Move userspace syscall dispatch outside of common entry
  arm64: Track the sigreturn landing pad location
  arm64: Enable userspace syscall dispatch
  arm64: tools: Update syscall user dispatch tests

 arch/Kconfig                                  |  4 ++++
 arch/arm64/Kconfig                            |  1 +
 arch/arm64/include/asm/syscall.h              |  2 ++
 arch/arm64/include/asm/thread_info.h          |  4 +++-
 arch/arm64/kernel/ptrace.c                    | 24 +++++++++++++++++++
 arch/arm64/kernel/syscall.c                   |  9 +++++++
 arch/arm64/kernel/vdso/sigreturn.S            |  1 +
 arch/arm64/kernel/vdso/vdso.lds.S             |  1 +
 include/linux/syscall_user_dispatch.h         |  4 +++-
 kernel/entry/Makefile                         |  3 ++-
 kernel/entry/common.c                         |  3 +--
 kernel/entry/common.h                         |  7 ------
 kernel/entry/syscall_user_dispatch.c          |  2 --
 .../syscall_user_dispatch/sud_benchmark.c     |  2 +-
 .../syscall_user_dispatch/sud_test.c          |  9 +++++++
 15 files changed, 61 insertions(+), 15 deletions(-)
 delete mode 100644 kernel/entry/common.h

-- 
2.30.2