linux-kernel - Re: [PATCH 2/3] arm64: pageattr: Use walk_page_range

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Message-ID: <58d53c0a-1b61-4276-bdd5-9eb2e583f865@arm.com>
Date: Mon, 9 Jun 2025 15:11:59 +0530
From: Dev Jain <dev.jain@....com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: akpm@...ux-foundation.org, david@...hat.com, catalin.marinas@....com,
 will@...nel.org, Liam.Howlett@...cle.com, vbabka@...e.cz, rppt@...nel.org,
 surenb@...gle.com, mhocko@...e.com, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, suzuki.poulose@....com, steven.price@....com,
 gshan@...hat.com, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 2/3] arm64: pageattr: Use walk_page_range_novma() to
 change memory permissions


On 06/06/25 3:19 pm, Lorenzo Stoakes wrote:
> On Fri, May 30, 2025 at 02:34:06PM +0530, Dev Jain wrote:
>> Move away from apply_to_page_range(), which does not honour leaf mappings,
>> to walk_page_range_novma(). The callbacks emit a warning and return EINVAL
>> if a partial range is detected.
> Hm a follow up question here - why not just improve apply_to_page_range() to
> honour leaf mappings?
>
> What does honouring leaf mappings actually mean? You mean handling huge pages?
>
> Would it be all that difficult to implement?
>
> It seems like you're pushing a bunch of the 'applying' logic over from there to
> a walker that isn't maybe best suited to it and having to introduce an iffy new
> form of locking...
>
> Can we go vice-versa? :)
>
> Also obviously walk_page_range_novma() doesn't exist any more :P
> walk_kernel_page_table_range() is the preferred solution.

I cannot see this function in mm-unstable. Also, mm-unstable is broken - I get
some RCU message in dmesg, and after some 20-30 second delay the kernel boots.
So on which branch do I base my work on...

>