[PATCH v3 20/28] arm64/sve: Add prctl controls for userspace vector length management

[Catalin Marinas]

On Tue, Oct 10, 2017 at 07:38:37PM +0100, Dave P Martin wrote:
> This patch adds two arm64-specific prctls, to permit userspace to
> control its vector length:
> 
>  * PR_SVE_SET_VL: set the thread's SVE vector length and vector
>    length inheritance mode.
> 
>  * PR_SVE_GET_VL: get the same information.
> 
> Although these calls shadow instruction set features in the SVE
> architecture, these prctls provide additional control: the vector
> length inheritance mode is Linux-specific and nothing to do with
> the architecture, and the architecture does not permit EL0 to set
> its own vector length directly.  Both can be used in portable tools
> without requiring the use of SVE instructions.
> 
> Signed-off-by: Dave Martin <Dave.Martin at arm.com>
> Cc: Alex Bennée <alex.bennee at linaro.org>

Reviewed-by: Catalin Marinas <catalin.marinas at arm.com>