linux-kernel - Re: [PATCH] s390/uaccess: introduce bit field for OAC specifier

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Date:   Fri, 14 Jan 2022 14:58:48 +0100
From:   Heiko Carstens <hca@...ux.ibm.com>
To:     Janis Schoetterl-Glausch <scgl@...ux.ibm.com>
Cc:     Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Nico Boehr <nrb@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] s390/uaccess: introduce bit field for OAC specifier

On Tue, Jan 11, 2022 at 11:00:03AM +0100, Janis Schoetterl-Glausch wrote:
> From: Nico Boehr <nrb@...ux.ibm.com>
> 
> Previously, we've used  magic values to specify the OAC
> (operand-access control) for mvcos.
> 
> Instead we introduce a bit field for it.
> 
> When using a bit field, we cannot use an immediate value with K
> constraint anymore, since GCC older than 10 doesn't recognize
> the bit field union as a compile time constant.
> To make things work with older compilers,
> load the OAC value through a register.
> 
> Bloat-o-meter reports a slight increase in kernel size with this change:
> Total: Before=15692135, After=15693015, chg +0.01%
> 
> Signed-off-by: Nico Boehr <nrb@...ux.ibm.com>
> Co-developed-by: Janis Schoetterl-Glausch <scgl@...ux.ibm.com>
> Signed-off-by: Janis Schoetterl-Glausch <scgl@...ux.ibm.com>
> ---
>  arch/s390/include/asm/uaccess.h | 120 ++++++++++++++++++++------------
>  arch/s390/lib/uaccess.c         |  24 +++++--
>  2 files changed, 95 insertions(+), 49 deletions(-)

Applied with a couple of indentation + whitespace fixes.

Thanks!