linux-kernel - Re: [PATCH v8 0/5] arm64: support FEAT_BBM level 2 and large block mapping when rodata=full

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Message-ID: <9b2d3ddd-ffee-4b54-ae38-6412516c3f07@os.amperecomputing.com>
Date: Fri, 19 Sep 2025 07:55:56 -0700
From: Yang Shi <yang@...amperecomputing.com>
To: Will Deacon <will@...nel.org>, catalin.marinas@....com,
 ryan.roberts@....com, akpm@...ux-foundation.org, david@...hat.com,
 lorenzo.stoakes@...cle.com, ardb@...nel.org, dev.jain@....com,
 scott@...amperecomputing.com, cl@...two.org
Cc: kernel-team@...roid.com, linux-arm-kernel@...ts.infradead.org,
 linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v8 0/5] arm64: support FEAT_BBM level 2 and large block
 mapping when rodata=full



On 9/18/25 2:10 PM, Will Deacon wrote:
> On Wed, 17 Sep 2025 12:02:06 -0700, Yang Shi wrote:
>> On systems with BBML2_NOABORT support, it causes the linear map to be mapped
>> with large blocks, even when rodata=full, and leads to some nice performance
>> improvements.
>>
>> Ryan tested v7 on an AmpereOne system (a VM with 12G RAM) in all 3 possible
>> modes by hacking the BBML2 feature detection code:
>>
>> [...]
> Applied patches 1 and 3 to arm64 (for-next/mm), thanks!
>
> [1/5] arm64: Enable permission change on arm64 kernel block mappings
>        https://git.kernel.org/arm64/c/a660194dd101
> [3/5] arm64: mm: support large block mapping when rodata=full
>        https://git.kernel.org/arm64/c/a166563e7ec3
>
> I also picked up the BBML allow-list addition (second patch) on
> for-next/cpufeature.

Hi Will,

Thank you so much!

>
> The fourth patch ("arm64: mm: split linear mapping if BBML2 unsupported
> on secondary CPUs") has some really horrible conflicts. These are partly
> due to some of the type cleanups on for-next/mm but I think mainly due
> to Kevin's kpti rework that landed after -rc1.
>
> So I think the best bet might be to leave that one for next time, if
> that's ok?

I saw you and Ryan just figured out how to move forward. You guys are 
definitely more knowledgeable than me regarding the asymmetric systems.

Thanks,
Yang

>
> Cheers,