[v2,0/3] arm64/sve: Document our actual SVE syscall ABI

Message

Mark Brown Aug. 15, 2022, 1:26 p.m. UTC

Currently our SVE syscall ABI documentation does not reflect the actual
implemented ABI, it says that register state not shared with FPSIMD
becomes undefined on syscall when in reality we always clear it. Since
changing this would cause a change in the observed kernel behaviour
there is a substantial desire to avoid taking advantage of the
documented ABI so instead let's document what we actually do so it's
clear that it is in reality an ABI.

There has been some pushback on tightening the documentation in the past
but it is hard to see who that helps, it makes the implementation
decisions less clear and makes it harder for people to discover and make
use of the actual ABI. The main practical concern is that qemu's user
mode does not currently flush the registers.

v2:
 - Rebase onto v6.0-rc1.

Mark Brown (3):
  kselftest/arm64: Correct buffer allocation for SVE Z registers
  arm64/sve: Document our actual ABI for clearing registers on syscall
  kselftest/arm64: Enforce actual ABI for SVE syscalls

 Documentation/arm64/sve.rst                   |  2 +-
 .../testing/selftests/arm64/abi/syscall-abi.c | 61 ++++++++++++-------
 2 files changed, 41 insertions(+), 22 deletions(-)


base-commit: 568035b01cfb107af8d2e4bd2fb9aea22cf5b868