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Implement support for a new note type NT_ARM64_ZT providing access to ZT0 when implemented. Since ZT0 is a register with constant size this is much simpler than for other SME state. As ZT0 is only accessible when PSTATE.ZA is set writes to ZT0 cause PSTATE.ZA to be set, the main alternative would be to return -EBUSY in this case but this seemed more constructive. Practical users are also going to be working with ZA anyway and have some understanding of the state. Signed-off-by: Mark Brown <broonie@kernel.org> Link: https://lore.kernel.org/r/20221208-arm64-sme2-v4-12-f2fa0aef982f@kernel.org Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>