linux-kernel - Re: kernel BUG at arch/arm64/mm/mmu.c:185!

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Message-ID: <b39a37c8-c9b5-406d-a97a-24fa67622b49@arm.com>
Date: Tue, 25 Feb 2025 09:47:30 +0000
From: Ryan Roberts <ryan.roberts@....com>
To: Luiz Capitulino <luizcap@...hat.com>, LKML
 <linux-kernel@...r.kernel.org>, linux-mm@...ck.org
Cc: ardb@...nel.org,
 "linux-arm-kernel@...ts.infradead.org"
 <linux-arm-kernel@...ts.infradead.org>,
 Catalin Marinas <Catalin.Marinas@....com>, Will Deacon <will@...nel.org>
Subject: Re: kernel BUG at arch/arm64/mm/mmu.c:185!

(Adding arm folks for visibility)

See original report here for context:
https://lore.kernel.org/all/a3d9acbe-07c2-43b6-9ba9-a7585f770e83@redhat.com/

TL;DR is that 6.14 doesn't boot on Ampere Altra when kaslr is enabled.

On 20/02/2025 20:08, Luiz Capitulino wrote:
> On 2025-02-19 09:40, Luiz Capitulino wrote:
> 
>>>> Btw, I'll try to bisect again and will also try to update the system's firmware
>>>> just in case.
> 
> I tried to bisect it and again, got nowhere.
> 
> Git bisect says the first bad commit is 8883957b3c9de2087fb6cf9691c1188cccf1ac9c .
> But I'm able to boot that tree...
> 

OK, think I've found the dodgy commit:

Commit 62cffa496aac ("arm64/mm: Override PARange for !LPA2 and use it consistently")

Based on the changes it certainly looks like it could be the issue, but I
haven't spotted exactly what the problem is yet. Ard, could you take a look?

I managed to hack multi ram bank support into kvmtool, so I can now repro the
issue in virtualization. Then was able to bisect to get to the above commit.

I'll keep digging to see if I can get to the root cause, but I suspect Ard is
best placed to hypothesise at this point.

Thanks,
Ryan