linux-kernel - RE: [PATCH v8 2/2] lib: checksum: Use aligned accesses for ip_fast_csum and csum_ipv6

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Message-ID: <a7e9691432374000b9566a0201d004e6@AcuMS.aculab.com>
Date: Thu, 15 Feb 2024 10:27:13 +0000
From: David Laight <David.Laight@...LAB.COM>
To: 'Guenter Roeck' <linux@...ck-us.net>, Charlie Jenkins
	<charlie@...osinc.com>, Palmer Dabbelt <palmer@...belt.com>, Andrew Morton
	<akpm@...ux-foundation.org>, Helge Deller <deller@....de>, "James E.J.
 Bottomley" <James.Bottomley@...senpartnership.com>, Parisc List
	<linux-parisc@...r.kernel.org>, Al Viro <viro@...iv.linux.org.uk>
CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v8 2/2] lib: checksum: Use aligned accesses for
 ip_fast_csum and csum_ipv6_magic tests

...
> It would be worthwhile tracking this down since there are
> lots of unaligned data accesses (8-byte accesses on 4-byte aligned addresses)
> when running the kernel in 64-bit mode.

Hmmm....
For performance reasons you really don't want any of them.
The misaligned 64bit fields need an __attribute((aligned(4)) marker.

If the checksum code can do them it really needs to detect
and handle the misalignment.

The misaligned trap handler probably ought to contain a
warn_on_once() to dump stack on the first such error.
They can then be fixed one at a time.

	David

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