linux-kernel - Re: [PATCH v3 07/22] checkpatch: Warn on page table access without accessors

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Message-ID: <1dfa1e3566cafbe43a1d4753defef9c82ddb3b64.camel@perches.com>
Date: Wed, 12 Nov 2025 18:21:01 -0800
From: Joe Perches <joe@...ches.com>
To: Samuel Holland <samuel.holland@...ive.com>, Palmer Dabbelt	
 <palmer@...belt.com>, Paul Walmsley <pjw@...nel.org>, 
	linux-riscv@...ts.infradead.org, Andrew Morton <akpm@...ux-foundation.org>,
  David Hildenbrand	 <david@...hat.com>, linux-mm@...ck.org
Cc: devicetree@...r.kernel.org, Suren Baghdasaryan <surenb@...gle.com>, 
	linux-kernel@...r.kernel.org, Mike Rapoport <rppt@...nel.org>, Michal Hocko
	 <mhocko@...e.com>, Conor Dooley <conor@...nel.org>, Lorenzo Stoakes	
 <lorenzo.stoakes@...cle.com>, Krzysztof Kozlowski <krzk+dt@...nel.org>, 
 Alexandre Ghiti	 <alex@...ti.fr>, Emil Renner Berthing <kernel@...il.dk>,
 Rob Herring	 <robh+dt@...nel.org>, Vlastimil Babka <vbabka@...e.cz>, "Liam
 R . Howlett"	 <Liam.Howlett@...cle.com>, Andy Whitcroft
 <apw@...onical.com>, Dwaipayan Ray	 <dwaipayanray1@...il.com>, Lukas
 Bulwahn <lukas.bulwahn@...il.com>
Subject: Re: [PATCH v3 07/22] checkpatch: Warn on page table access without
 accessors

On Wed, 2025-11-12 at 17:45 -0800, Samuel Holland wrote:
> Architectures may have special rules for accessing the hardware page
> tables (for example, atomicity/ordering requirements), so the generic MM
> code provides the pXXp_get() and set_pXX() hooks for architectures to
> implement. These accessor functions are often omitted where a raw
> pointer dereference is believed to be safe (i.e. race-free). However,
> RISC-V needs to use these hooks to rewrite the page table values at
> read/write time on some platforms. A raw pointer dereference will no
> longer produce the correct value on those platforms, so the generic code
> must always use the accessor functions.
[]
> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
[]
> @@ -7721,6 +7721,13 @@ sub process {
>  				ERROR("MISSING_SENTINEL", "missing sentinel in ID array\n" . "$here\n$stat\n");
>  			}
>  		}
> +
> +# check for raw dereferences of hardware page table pointers
> +		if ($realfile !~ m@...ch/@ &&
> +		    $line =~ /(?<!pte_t |p[mu4g]d_t |izeof\()\*\(?(vmf(\.|->))?(pte|p[mu4g]d)p?\b/) {
> +			WARN("PAGE_TABLE_ACCESSORS",
> +			     "Use $3p_get()/set_$3() instead of dereferencing page table pointers\n" . $herecurr);
> +		}
>  	}

Seems like a lot of matches

$ git grep -P '(?<!pte_t |p[mu4g]d_t |izeof\()\*\(?(vmf(\.|->))?(pte|p[mu4g]d)p?\b' | \
  grep -v '^arch/' | wc -l
766

Is this really appropriate?

trivia:

izeof is really odd looking.  I'd prefer sizeof.