linux-kernel - Re: [PATCH v2 00/20] arm64: Move kernel mode FPSIMD buffer to the stack

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Message-ID: <20251003202849.GB24598@quark>
Date: Fri, 3 Oct 2025 13:28:49 -0700
From: Eric Biggers <ebiggers@...nel.org>
To: Ard Biesheuvel <ardb+git@...gle.com>
Cc: linux-arm-kernel@...ts.infradead.org, linux-crypto@...r.kernel.org,
	linux-kernel@...r.kernel.org, herbert@...dor.apana.org.au,
	linux@...linux.org.uk, Ard Biesheuvel <ardb@...nel.org>,
	Marc Zyngier <maz@...nel.org>, Will Deacon <will@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Kees Cook <keescook@...omium.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Mark Brown <broonie@...nel.org>
Subject: Re: [PATCH v2 00/20] arm64: Move kernel mode FPSIMD buffer to the
 stack

On Wed, Oct 01, 2025 at 11:02:02PM +0200, Ard Biesheuvel wrote:
> From: Ard Biesheuvel <ardb@...nel.org>
> 
> Move the buffer for preserving/restoring the kernel mode FPSIMD state on a
> context switch out of struct thread_struct, and onto the stack, so that
> the memory cost is not imposed needlessly on all tasks in the system.
> 
> Changes since v1:
> - Add a patch reverting the arm64 support for the generic
>   kernel_fpu_begin()/end() API, which is problematic on arm64.
> 
> - Introduce a new 'ksimd' scoped guard that encapsulates the calls the
>   kernel_neon_begin() and kernel_neon_end() at a higher level of
>   abstraction. This makes it straight-forward to plumb in the stack
>   buffer without complicating the callers.
> 
> - Move all kernel mode NEON users on arm64 (and some on ARM) over to the
>   new API.
> 
> - Add Mark's ack to patches #6 - #8
> 
> Cc: Marc Zyngier <maz@...nel.org>
> Cc: Will Deacon <will@...nel.org>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Mark Brown <broonie@...nel.org>
> Cc: Eric Biggers <ebiggers@...nel.org>
> 
> Ard Biesheuvel (20):
>   arm64: Revert support for generic kernel mode FPU
>   arm64/simd: Add scoped guard API for kernel mode SIMD
>   ARM/simd: Add scoped guard API for kernel mode SIMD
>   crypto: aegis128-neon - Move to more abstract 'ksimd' guard API
>   raid6: Move to more abstract 'ksimd' guard API
>   crypto/arm64: aes-ce-ccm - Avoid pointless yield of the NEON unit
>   crypto/arm64: sm4-ce-ccm - Avoid pointless yield of the NEON unit
>   crypto/arm64: sm4-ce-gcm - Avoid pointless yield of the NEON unit
>   lib/crc: Switch ARM and arm64 to 'ksimd' scoped guard API
>   lib/crypto: Switch ARM and arm64 to 'ksimd' scoped guard API
>   crypto/arm64: aes-ccm - Switch to 'ksimd' scoped guard API
>   crypto/arm64: aes-blk - Switch to 'ksimd' scoped guard API
>   crypto/arm64: aes-gcm - Switch to 'ksimd' scoped guard API
>   crypto/arm64: nhpoly1305 - Switch to 'ksimd' scoped guard API
>   crypto/arm64: polyval - Switch to 'ksimd' scoped guard API
>   crypto/arm64: sha3 - Switch to 'ksimd' scoped guard API
>   crypto/arm64: sm3 - Switch to 'ksimd' scoped guard API
>   crypto/arm64: sm4 - Switch to 'ksimd' scoped guard API
>   arm64/xorblocks:  Switch to 'ksimd' scoped guard API
>   arm64/fpsimd: Allocate kernel mode FP/SIMD buffers on the stack

Reviewed-by: Eric Biggers <ebiggers@...nel.org>

- Eric