linux-kernel - Re: [PATCH v10] lib: checksum: Use aligned accesses for ip_fast_csum and csum_ipv6

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Date: Tue, 27 Feb 2024 21:19:03 -0800
From: Guenter Roeck <linux@...ck-us.net>
To: David Laight <David.Laight@...LAB.COM>,
 Charlie Jenkins <charlie@...osinc.com>,
 Christophe Leroy <christophe.leroy@...roup.eu>
Cc: "Russell King (Oracle)" <linux@...linux.org.uk>,
 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>, Arnd Bergmann <arnd@...db.de>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 Palmer Dabbelt <palmer@...osinc.com>,
 Linux ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v10] lib: checksum: Use aligned accesses for ip_fast_csum
 and csum_ipv6_magic tests

On 2/27/24 14:44, David Laight wrote:
> ..
>> This is the "known" list of failures. I don't currently run kunit tests
>> on nios2 or riscv32, for example, nor on any architectures with no qemu
>> support.
> 
> nios2 is definitely going to 'crash and burn' if you do a misaligned access.
> 

Curiously enough, it doesn't. I get lots of

kernel unaligned access @ 0xc848eb78; BADADDR 0xc86f1d01; cause=6, isn=0x20800017

but a checksum test with unaligned data does pass, so the kernel
somehow handles it. It does crash, later, though, if CONFIG_NET_TEST
is enabled. Apparently the gso tests trigger lots of unaligned
accesses, and those are just too much for the kernel to handle.

Guenter

> Although Intel (aka the Altera bit) are claiming current version
> of their Quartus fpga build software is the last one the will
> support the nios2.
> They are expecting everyone to move to a risc-v soft cpu instead.
> We aren't happy about that, I doubt some of the big telco's are
> either - I believe some mobile base stations have fpga with a
> lot of nios2 in them - almost certainly running with a few kB
> of code and data memory and running small control tasks.
> If you want to run Linux, find an fpga with an ARM core.
> 
> There are some solutions - like writing a compatible soft cpu.
> 
> 	David
> 
> -
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