On Fri, Feb 25, 2022 at 04:59:01PM +0000, Mark Brown wrote: > By default all SME operations in userspace will trap. When this happens > we allocate storage space for the SME register state, set up the SVE > registers and disable traps. We do not need to initialize ZA since the > architecture guarantees that it will be zeroed when enabled and when we > trap ZA is disabled. > > On syscall we exit streaming mode if we were previously in it and ensure > that all but the lower 128 bits of the registers are zeroed while > preserving the state of ZA. This follows the aarch64 PCS for SME, ZA > state is preserved over a function call and streaming mode is exited. > Since the traps for SME do not distinguish between streaming mode SVE > and ZA usage if ZA is in use rather than reenabling traps we instead > zero the parts of the SVE registers not shared with FPSIMD and leave SME > enabled, this simplifies handling SME traps. If ZA is not in use then we > reenable SME traps and fall through to normal handling of SVE. > > Signed-off-by: Mark Brown <broonie@xxxxxxxxxx> Reviewed-by: Catalin Marinas <catalin.marinas@xxxxxxx>
