linux-kernel - Re: [PATCH v3 1/2] arm64: pageattr: Use pagewalk API to change memory permissions

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Message-ID: <1c7ba21a-7038-4edf-8734-fdba0c617c52@arm.com>
Date: Thu, 19 Jun 2025 09:33:29 +0530
From: Dev Jain <dev.jain@....com>
To: Karim Manaouil <kmanaouil.dev@...il.com>,
 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,
 yang@...amperecomputing.com, ryan.roberts@....com, anshuman.khandual@....com
Subject: Re: [PATCH v3 1/2] arm64: pageattr: Use pagewalk API to change memory
 permissions


On 14/06/25 8:20 pm, Karim Manaouil wrote:
> On Fri, Jun 13, 2025 at 05:27:27PM +0100, Lorenzo Stoakes wrote:
>> On Fri, Jun 13, 2025 at 07:13:51PM +0530, Dev Jain wrote:
>>> +		if (WARN_ON_ONCE((next - addr) != PGDIR_SIZE))
>>> +			return -EINVAL;
>> I guess the point here is to assert that the searched range _entirely
>> spans_ the folio that the higher order leaf page table entry describes.
>>
>> I'm guessing this is desired.
>>
>> But I'm not sure this should be a warning?
>>
>> What if you happen to walk a range that isn't aligned like this?
> My understandging is that the caller must ensure that addr is
> pud/pmd/pte-aligned. But, imho, since -EINVAL is returned, I don't think
> the WARN_ON_ONCE() is needed.

I don't really have a strong opinion on this. Ryan may be better fitted
to answer.

>