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Message-ID: <1dfa1e3566cafbe43a1d4753defef9c82ddb3b64.camel@perches.com>
Subject: Re: [PATCH v3 07/22] checkpatch: Warn on page table access without
 accessors
From: Joe Perches <joe@perches.com>
To: Samuel Holland <samuel.holland@sifive.com>, Palmer Dabbelt	
 <palmer@dabbelt.com>, Paul Walmsley <pjw@kernel.org>, 
	linux-riscv@lists.infradead.org, Andrew Morton <akpm@linux-foundation.org>,
  David Hildenbrand	 <david@redhat.com>, linux-mm@kvack.org
Cc: devicetree@vger.kernel.org, Suren Baghdasaryan <surenb@google.com>, 
	linux-kernel@vger.kernel.org, Mike Rapoport <rppt@kernel.org>, Michal Hocko
	 <mhocko@suse.com>, Conor Dooley <conor@kernel.org>, Lorenzo Stoakes	
 <lorenzo.stoakes@oracle.com>, Krzysztof Kozlowski <krzk+dt@kernel.org>, 
 Alexandre Ghiti	 <alex@ghiti.fr>, Emil Renner Berthing <kernel@esmil.dk>,
 Rob Herring	 <robh+dt@kernel.org>, Vlastimil Babka <vbabka@suse.cz>, "Liam
 R . Howlett"	 <Liam.Howlett@oracle.com>, Andy Whitcroft
 <apw@canonical.com>, Dwaipayan Ray	 <dwaipayanray1@gmail.com>, Lukas
 Bulwahn <lukas.bulwahn@gmail.com>
Date: Wed, 12 Nov 2025 18:21:01 -0800
In-Reply-To: <20251113014656.2605447-8-samuel.holland@sifive.com>
References: <20251113014656.2605447-1-samuel.holland@sifive.com>
	 <20251113014656.2605447-8-samuel.holland@sifive.com>
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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@^arch/@ &&
> +		    $line =3D~ /(?<!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 poin=
ters\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.