linux-kernel - Re: [patch V5 01/12] ARM: uaccess: Implement missing __get_user_asm

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Message-ID: <afc2d92c-bace-4128-b3c8-106e81cfd420@efficios.com>
Date: Tue, 28 Oct 2025 09:35:03 -0400
From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To: Thomas Gleixner <tglx@...utronix.de>, LKML <linux-kernel@...r.kernel.org>
Cc: kernel test robot <lkp@...el.com>, Russell King <linux@...linux.org.uk>,
 linux-arm-kernel@...ts.infradead.org,
 Linus Torvalds <torvalds@...ux-foundation.org>, x86@...nel.org,
 Madhavan Srinivasan <maddy@...ux.ibm.com>,
 Michael Ellerman <mpe@...erman.id.au>, Nicholas Piggin <npiggin@...il.com>,
 Christophe Leroy <christophe.leroy@...roup.eu>,
 linuxppc-dev@...ts.ozlabs.org, Paul Walmsley <pjw@...nel.org>,
 Palmer Dabbelt <palmer@...belt.com>, linux-riscv@...ts.infradead.org,
 Heiko Carstens <hca@...ux.ibm.com>,
 Christian Borntraeger <borntraeger@...ux.ibm.com>,
 Sven Schnelle <svens@...ux.ibm.com>, linux-s390@...r.kernel.org,
 Andrew Cooper <andrew.cooper3@...rix.com>,
 David Laight <david.laight.linux@...il.com>,
 Julia Lawall <Julia.Lawall@...ia.fr>, Nicolas Palix <nicolas.palix@...g.fr>,
 Peter Zijlstra <peterz@...radead.org>, Darren Hart <dvhart@...radead.org>,
 Davidlohr Bueso <dave@...olabs.net>, André Almeida
 <andrealmeid@...lia.com>, Alexander Viro <viro@...iv.linux.org.uk>,
 Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
 linux-fsdevel@...r.kernel.org
Subject: Re: [patch V5 01/12] ARM: uaccess: Implement missing
 __get_user_asm_dword()

On 2025-10-27 04:43, Thomas Gleixner wrote:
> When CONFIG_CPU_SPECTRE=n then get_user() is missing the 8 byte ASM variant
> for no real good reason. This prevents using get_user(u64) in generic code.
> 
> Implement it as a sequence of two 4-byte reads with LE/BE awareness and
> make the unsigned long (or long long) type for the intermediate variable to
> read into dependend on the the target type.
> 
> The __long_type() macro and idea was lifted from PowerPC. Thanks to
> Christophe for pointing it out.

[...]

Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>


-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com