linux-kernel - Re: [PATCH v9 2/2] lib: checksum: Use aligned accesses for ip_fast_csum and csum_ipv6

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Date: Fri, 23 Feb 2024 06:49:41 -0800
From: Guenter Roeck <linux@...ck-us.net>
To: David Laight <David.Laight@...LAB.COM>,
 'Christophe Leroy' <christophe.leroy@...roup.eu>,
 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>,
 "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
 "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH v9 2/2] lib: checksum: Use aligned accesses for
 ip_fast_csum and csum_ipv6_magic tests

On 2/23/24 02:28, David Laight wrote:
> From: Christophe Leroy
>> Sent: 23 February 2024 10:07
> ...
>>> +/* Ethernet headers are 14 bytes and NET_IP_ALIGN is used to align them */
>>> +#define IP_ALIGNMENT (14 + NET_IP_ALIGN)
>>
>> Only if no VLAN.
>>
>> When using VLANs it is 4 bytes more. But why do you mind that at all ?
> 
> Wasn't one architecture faulting on a double-register read?
> Where that had to be aligned (probably 8 bytes) but a normal
> memory read could be misaligned?
> 

That was hppa64, and the problem was with its qemu emulation,
not with this code.

Guenter