linux-kernel - Re: [PATCH v4 0/5] Fix accurate exception reporting in SPARC assembly

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Message-ID: <8d32507a-dd01-4785-946d-00ad28b1fd58@gaisler.com>
Date: Fri, 19 Sep 2025 20:03:50 +0200
From: Andreas Larsson <andreas@...sler.com>
To: Michael Karcher <kernel@...rcher.dialup.fu-berlin.de>
Cc: sparclinux@...r.kernel.org, linux-kernel@...r.kernel.org,
 John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>,
 Anthony Yznaga <anthony.yznaga@...cle.com>, René Rebe
 <rene@...ctcode.com>, Jonathan 'theJPster' Pallant
 <kernel@...jpster.org.uk>, Magnus Lindholm <linmag7@...il.com>,
 Tony Rodriguez <unixpro1970@...il.com>
Subject: Re: [PATCH v4 0/5] Fix accurate exception reporting in SPARC assembly

On 2025-09-05 00:03, Michael Karcher wrote:
> In 2018, David Miller implemented accurate exception reporting in
> copy_from_user and copy_to_user by handling exceptions on each load
> or store instruction that accesses userspace memory and calculating
> the remaining bytes from the processor context. As issues with
> transparent huge page support and folio support in ext4 were due
> to a bogus return value from copy_from_user, I wrote a comprehensive
> testsuite for the generic variant, and the machine-specific variants
> for UltraSPARC I/II, UltraSPARC III, Niagara, Niagara 2/3,
> Niagara 4 and M7, see
> 
> https://github.com/karcherm/sparc-cfu-bug-reproducer
> 
> despite the name of the project, it does not only test copy_from_user,
> but also copy_to_user, and it also contains fixes to a very small amount
> of exception handler references that were calculating the result in
> a wrong way.
> 
> For UltraSPARC III, I chose to adjust the memcpy code itself instead of
> adding complexity to multiple exception handlers. That fix has already
> been tested to fix stability issues observed by Adrian Glaubitz which
> kicked off the investigation. On all other architectures, the changes
> are just to the exception handlers.
> 
> Kind regards,
>   Michael Karcher
> 
> Signed-off-by: Michael Karcher <kernel@...rcher.dialup.fu-berlin.de>
> ---
> Changes in v4:
> - Add further credit for running tests on machines with this patch applied
> - Link to v3: https://lore.kernel.org/r/20250904-memcpy_series-v3-0-906655a5a7ad@mkarcher.dialup.fu-berlin.de
> 
> Changes in v3:
> - Fix bad formatting in commit messages (missing line wrap,
>   extra empty line after Fixes:)
> - Consistently add hardware to Tested-By lines
> - Link to v2: https://lore.kernel.org/r/20250904-memcpy_series-v2-0-9806dd1784e7@mkarcher.dialup.fu-berlin.de
> 
> Changes in v2:
> - More verbose description on how these issues were found
> - Add M7 change, previously separate in
>   https://lore.kernel.org/r/20250828121844.2250-1-kernel@mkarcher.dialup.fu-berlin.de
> - Link to v1: https://lore.kernel.org/r/20250826160312.2070-1-kernel@mkarcher.dialup.fu-berlin.de
> 
> ---
> Michael Karcher (5):
>       sparc: fix accurate exception reporting in copy_{from_to}_user for UltraSPARC
>       sparc: fix accurate exception reporting in copy_{from_to}_user for UltraSPARC III
>       sparc: fix accurate exception reporting in copy_{from_to}_user for Niagara
>       sparc: fix accurate exception reporting in copy_to_user for Niagara 4
>       sparc: fix accurate exception reporting in copy_{from,to}_user for M7
> 
>  arch/sparc/lib/M7memcpy.S     | 20 ++++++++++----------
>  arch/sparc/lib/Memcpy_utils.S |  9 +++++++++
>  arch/sparc/lib/NG4memcpy.S    |  2 +-
>  arch/sparc/lib/NGmemcpy.S     | 29 ++++++++++++++++++-----------
>  arch/sparc/lib/U1memcpy.S     | 19 ++++++++++---------
>  arch/sparc/lib/U3memcpy.S     |  2 +-
>  6 files changed, 49 insertions(+), 32 deletions(-)
> ---
> base-commit: b320789d6883cc00ac78ce83bccbfe7ed58afcf0
> change-id: 20250902-memcpy_series-b3bdd5542ca7

Reviewed-by: Andreas Larsson <andreas@...sler.com>

Picking this up to my for-next.

Thanks,
Andreas