linux-kernel - Re: [PATCH] ALSA: pcm: Convert multiple {get/put}_user to user_access_begin/user_access

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Message-ID: <20250610205358.07b1cc05@pumpkin>
Date: Tue, 10 Jun 2025 20:53:58 +0100
From: David Laight <david.laight.linux@...il.com>
To: Christophe Leroy <christophe.leroy@...roup.eu>
Cc: Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>,
 linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
 linux-sound@...r.kernel.org, Herve Codina <herve.codina@...tlin.com>, Mark
 Brown <broonie@...nel.org>
Subject: Re: [PATCH] ALSA: pcm: Convert multiple {get/put}_user to
 user_access_begin/user_access_end()

On Sat,  7 Jun 2025 13:37:42 +0200
Christophe Leroy <christophe.leroy@...roup.eu> wrote:

> With user access protection (Called SMAP on x86 or KUAP on powerpc)
> each and every call to get_user() or put_user() performs heavy
> operations to unlock and lock kernel access to userspace.
> 
> To avoid that, perform user accesses by blocks using
> user_access_begin/user_access_end() and unsafe_get_user()/
> unsafe_put_user() and alike.

Did you consider using masked_user_access_begin() ?
It removes a conditional branch and lfence as well.

	David