From: Catalin Marinas <catalin.marinas@arm.com>

On Wed, 15 Oct 2025 18:56:35 +0100, Mark Brown wrote:

Currently it is not possible to disable streaming mode via ptrace on SME
only systems, the interface for doing this is to write via NT_ARM_SVE but
such writes will be rejected on a system without SVE support. Enable this
functionality by allowing userspace to write SVE_PT_REGS_FPSIMD format data
via NT_ARM_SVE with the vector length set to 0 on SME only systems. Such
writes currently error since we require that a vector length is specified
which should minimise the risk that existing software is relying on current
behaviour.

[...]

I don't think we'll get gdb feedback soon. Thanks David for the LLDB
ack.

Applied to arm64 (for-next/sme-ptrace-disable), thanks!

[1/3] arm64/sme: Support disabling streaming mode via ptrace on SME only systems
      https://git.kernel.org/arm64/c/472800cd5e38
[2/3] kselftst/arm64: Test NT_ARM_SVE FPSIMD format writes on non-SVE systems
      https://git.kernel.org/arm64/c/eb9df6d69a96
[3/3] kselftest/arm64: Cover disabling streaming mode without SVE in fp-ptrace
      https://git.kernel.org/arm64/c/a0245b42f881

-- 
Catalin