kselftest/arm64: Add SME2 coverage to syscall-abi

Verify that ZT0 is preserved over syscalls when it is present and
PSTATE.ZA is set.

Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20221208-arm64-sme2-v4-19-f2fa0aef982f@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

kselftest/arm64: Verify SME only ABI in syscall-abi

Currently syscall-abi only covers SME in the case where the system supports
SVE however it is architecturally valid to support SME without SVE. Update
the program to cover this case, this requires adjustments in the code to
check for SVCR.SM being set when deciding if we're handling the FPSIMD or
SVE registers and the addition of new test cases for the SME only case.

Note that in the SME only case we should not save the SVE registers after a
syscall since even if we were in streaming mode and therefore set them the
syscall should have exited streaming mode, we check that we have done so by
looking at SVCR.

Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20221223-arm64-syscall-abi-sme-only-v1-3-4fabfbd62087@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

kselftest/arm64: Use preferred form for predicate load/stores

The preferred form of the str/ldr for predicate registers with an immediate
of zero is to omit the zero, and the clang built in assembler rejects the
zero immediate. Drop the immediate.

Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20221117114130.687261-1-broonie@kernel.org
Signed-off-by: Will Deacon <will@kernel.org>

kselftest/arm64: Add SME support to syscall ABI test

For every possible combination of SVE and SME vector length verify that for
each possible value of SVCR after a syscall we leave streaming mode and ZA
is preserved. We don't need to take account of any streaming/non streaming
SVE vector length changes in the assembler code since the store instructions
will handle the vector length for us. We log if the system supports FA64 and
only try to set FFR in streaming mode if it does.

Signed-off-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Shuah Khan <skhan@linuxfoundation.org>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20220419112247.711548-39-broonie@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

kselftest/arm64: Add a test program to exercise the syscall ABI

Currently we don't have any coverage of the syscall ABI so let's add a very
dumb test program which sets up register patterns, does a sysscall and then
checks that the register state after the syscall matches what we expect.
The program is written in an extremely simplistic fashion with the goal of
making it easy to verify that it's doing what it thinks it's doing, it is
not a model of how one should write actual code.

Currently we validate the general purpose, FPSIMD and SVE registers. There
are other thing things that could be covered like FPCR and flags registers,
these can be covered incrementally - my main focus at the minute is
covering the ABI for the SVE registers.

The program repeats the tests for all possible SVE vector lengths in case
some vector length specific optimisation causes issues, as well as testing
FPSIMD only. It tries two syscalls, getpid() and sched_yield(), in an
effort to cover both immediate return to userspace and scheduling another
task though there are no guarantees which cases will be hit.

A new test directory "abi" is added to hold the test, it doesn't seem to
fit well into any of the existing directories.

Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20211210184133.320748-7-broonie@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>