linux-kernel - Re: [PATCH] arm64/mm: Add a fallback stub for pgd_page

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Message-ID: <aQuDdE_Tj3di7q3P@willie-the-truck>
Date: Wed, 5 Nov 2025 17:03:48 +0000
From: Will Deacon <will@...nel.org>
To: Anshuman Khandual <anshuman.khandual@....com>
Cc: linux-arm-kernel@...ts.infradead.org, ryan.roberts@....com,
	Catalin Marinas <catalin.marinas@....com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64/mm: Add a fallback stub for pgd_page_paddr()

On Wed, Nov 05, 2025 at 08:24:40AM +0530, Anshuman Khandual wrote:
> On 04/11/25 8:01 PM, Will Deacon wrote:
> > On Tue, Oct 14, 2025 at 12:06:33PM +0100, Anshuman Khandual wrote:
> >> Add a fallback stub for pgd_page_paddr() when (PGTBALE_LEVELS <= 4) which
> > 
> > typo
> 
> Sure will change - s/Add/Adds
> > 
> >> helps in intercepting any unintended usage and which is also in line with
> >> existing stubs for similar [pud|p4d]_page_paddr() helpers.
> > 
> > Are you saying the kernel compiles in this case without your patch? Which
> > definition of pgd_page_paddr() does it end up using?
> 
> Kernel compiles for PGTBALE_LEVELS <= 4 just fine without this patch as both
> its current users p4d_offset_phys() and p4d_offset_lockless() are wrapped in
> with PGTBALE_LEVELS > 4.

Ok, but your patch is trying to catch broken users of the macro, right?
So my question is, would such a user compile today? If not, then your
patch is pointless.

Will