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Re: [PATCH v3 20/28] arm64/sve: Add prctl controls for userspace vector length management
- From: Catalin Marinas <catalin dot marinas at arm dot com>
- To: Dave Martin <Dave dot Martin at arm dot com>
- Cc: linux-arm-kernel at lists dot infradead dot org, linux-arch at vger dot kernel dot org, Okamoto Takayuki <tokamoto at jp dot fujitsu dot com>, libc-alpha at sourceware dot org, Ard Biesheuvel <ard dot biesheuvel at linaro dot org>, Szabolcs Nagy <szabolcs dot nagy at arm dot com>, Will Deacon <will dot deacon at arm dot com>, Richard Sandiford <richard dot sandiford at arm dot com>, Alex Bennée <alex dot bennee at linaro dot org>, kvmarm at lists dot cs dot columbia dot edu
- Date: Thu, 12 Oct 2017 18:11:17 +0100
- Subject: Re: [PATCH v3 20/28] arm64/sve: Add prctl controls for userspace vector length management
- Authentication-results: sourceware.org; auth=none
- References: <1507660725-7986-1-git-send-email-Dave.Martin@arm.com> <1507660725-7986-21-git-send-email-Dave.Martin@arm.com>
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@arm.com>
> Cc: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>