Re: [PATCH v11 17/40] arm64/sme: Implement ZA context switching

On Mon, Feb 07, 2022 at 03:20:46PM +0000, Mark Brown wrote:

Allocate space for storing ZA on first access to SME and use that to save and restore ZA state when context switching. We do this by using the vector form of the LDR and STR ZA instructions, these do not require streaming mode and have implementation recommendations that they avoid contention issues in shared SMCU implementations.

Since ZA is architecturally guaranteed to be zeroed when enabled we do not need to explicitly zero ZA, either we will be restoring from a saved copy or trapping on first use of SME so we know that ZA must be disabled.

Signed-off-by: Mark Brown broonie@kernel.org

Reviewed-by: Catalin Marinas catalin.marinas@arm.com