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

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Message-ID: <20250614145021.7yve56wcxf3dlvwg@ed.ac.uk>
Date: Sat, 14 Jun 2025 15:50:21 +0100
From: Karim Manaouil <kmanaouil.dev@...il.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: Dev Jain <dev.jain@....com>, 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 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.

-- 
~karim