Re: [PATCH 5.1 51/55] bpf, arm64: use more scalable stadd over ldxr / stxr loop in xadd

[Sasha Levin]

On Tue, Jul 02, 2019 at 10:01:59AM +0200, Greg Kroah-Hartman wrote:
> From: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
>
> commit 34b8ab091f9ef57a2bb3c8c8359a0a03a8abf2f9 upstream.
>
> Since ARMv8.1 supplement introduced LSE atomic instructions back in 2016,
> lets add support for STADD and use that in favor of LDXR / STXR loop for
> the XADD mapping if available. STADD is encoded as an alias for LDADD with
> XZR as the destination register, therefore add LDADD to the instruction
> encoder along with STADD as special case and use it in the JIT for CPUs
> that advertise LSE atomics in CPUID register. If immediate offset in the
> BPF XADD insn is 0, then use dst register directly instead of temporary
> one.
>
> Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
> Acked-by: Jean-Philippe Brucker <jean-philippe.brucker@xxxxxxx>
> Acked-by: Will Deacon <will.deacon@xxxxxxx>
> Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

This one has a fix upstream: c5e2edeb01ae9ffbdde95bdcdb6d3614ba1eb195
("arm64: insn: Fix ldadd instruction encoding").

--
Thanks,
Sasha