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From:   Linus Walleij <linus.walleij@linaro.org>
Date:   Thu, 15 Dec 2022 11:26:58 +0100
Message-ID: <CACRpkdYiHQQtw2=iPKos3sXEkeErTNxR7T0FPBrCqhQxtxhCkA@mail.gmail.com>
Subject: Re: [PATCH v2 2/2] ARM: permit non-nested kernel mode NEON in softirq context
To:     Ard Biesheuvel <ardb@kernel.org>
Cc:     linux-arm-kernel@lists.infradead.org, linux@armlinux.org.uk,
        linux-crypto@vger.kernel.org, Arnd Bergmann <arnd@arndb.de>
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On Wed, Dec 7, 2022 at 11:39 AM Ard Biesheuvel <ardb@kernel.org> wrote:

> We currently only permit kernel mode NEON in process context, to avoid
> the need to preserve/restore the NEON register file when taking an
> exception while running in the kernel.
>
> Like we did on arm64, we can relax this restriction substantially, by
> permitting kernel mode NEON from softirq context, while ensuring that
> softirq processing is disabled when the NEON is being used in task
> context. This guarantees that only NEON context belonging to user space
> needs to be preserved and restored, which is already taken care of.
>
> This is especially relevant for network encryption, where incoming
> frames are typically handled in softirq context, and deferring software
> decryption to a kernel thread or falling back to C code are both
> undesirable from a performance PoV.
>
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

So boosting WireGuard as primary SW network encryption user?
This is really neat, BTW:
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>

Yours,
Linus Walleij