linux-kernel - Re: [PATCH 2/2] asm-generic: add an optional pfn_valid check to page_to

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Message-ID: <9ee9c21b-179f-49aa-8c65-304c8ef2c9a7@csgroup.eu>
Date: Tue, 5 Nov 2024 10:56:42 +0100
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: Christoph Hellwig <hch@....de>, Arnd Bergmann <arnd@...db.de>
Cc: linux-alpha@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-snps-arc@...ts.infradead.org, linux-arm-kernel@...ts.infradead.org,
 linux-csky@...r.kernel.org, linux-hexagon@...r.kernel.org,
 loongarch@...ts.linux.dev, linux-m68k@...ts.linux-m68k.org,
 linux-mips@...r.kernel.org, linux-openrisc@...r.kernel.org,
 linux-parisc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
 linux-riscv@...ts.infradead.org, linux-s390@...r.kernel.org,
 linux-sh@...r.kernel.org, sparclinux@...r.kernel.org,
 linux-um@...ts.infradead.org, linux-arch@...r.kernel.org
Subject: Re: [PATCH 2/2] asm-generic: add an optional pfn_valid check to
 page_to_phys



Le 23/10/2024 à 07:36, Christoph Hellwig a écrit :
> page_to_pfn is usually implemented by pointer arithmetics on the memory
> map, which means that bogus input can lead to even more bogus output.
> 
> Powerpc had a pfn_valid check on the intermediate pfn in the page_to_phys
> implementation when CONFIG_DEBUG_VIRTUAL is defined, which seems
> generally useful, so add that to the generic version.
> 
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
>   include/asm-generic/memory_model.h | 10 ++++++++++
>   1 file changed, 10 insertions(+)
> 
> diff --git a/include/asm-generic/memory_model.h b/include/asm-generic/memory_model.h
> index a73a140cbecd..6d1fb6162ac1 100644
> --- a/include/asm-generic/memory_model.h
> +++ b/include/asm-generic/memory_model.h
> @@ -64,7 +64,17 @@ static inline int pfn_valid(unsigned long pfn)
>   #define page_to_pfn __page_to_pfn
>   #define pfn_to_page __pfn_to_page
>   
> +#ifdef CONFIG_DEBUG_VIRTUAL
> +#define page_to_phys(page)						\
> +({									\
> +	unsigned long __pfn = page_to_pfn(page);			\
> +									\
> +	WARN_ON_ONCE(!pfn_valid(__pfn));				\

On powerpc I think it was a WARN_ON().

Will a WARN_ON_ONCE() be enough ?

> +	PFN_PHYS(__pfn);						\
> +})
> +#else
>   #define page_to_phys(page)	PFN_PHYS(page_to_pfn(page))
> +#endif /* CONFIG_DEBUG_VIRTUAL */
>   #define phys_to_page(phys)	pfn_to_page(PHYS_PFN(phys))
>   
>   #endif /* __ASSEMBLY__ */