linux-kernel - Re: [PATCH] powerpc: Make virt_to

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Message-ID: <87y1icdaoq.fsf@mail.lhotse>
Date:   Tue, 15 Aug 2023 17:30:45 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Linus Walleij <linus.walleij@...aro.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, Linus Walleij <linus.walleij@...aro.org>
Subject: Re: [PATCH] powerpc: Make virt_to_pfn() a static inline

Linus Walleij <linus.walleij@...aro.org> writes:

> Making virt_to_pfn() a static inline taking a strongly typed
> (const void *) makes the contract of a passing a pointer of that
> type to the function explicit and exposes any misuse of the
> macro virt_to_pfn() acting polymorphic and accepting many types
> such as (void *), (unitptr_t) or (unsigned long) as arguments
> without warnings.
>
> Move the virt_to_pfn() and related functions below the
> declaration of __pa() so it compiles.
>
> For symmetry do the same with pfn_to_kaddr().
>
> As the file is included right into the linker file, we need
> to surround the functions with ifndef __ASSEMBLY__ so we
> don't cause compilation errors.
>
> The conversion moreover exposes the fact that pmd_page_vaddr()
> was returning an unsigned long rather than a const void * as
> could be expected, so all the sites defining pmd_page_vaddr()
> had to be augmented as well.
...
> diff --git a/arch/powerpc/include/asm/pgtable.h b/arch/powerpc/include/asm/pgtable.h
> index 6a88bfdaa69b..a9515d3d7831 100644
> --- a/arch/powerpc/include/asm/pgtable.h
> +++ b/arch/powerpc/include/asm/pgtable.h
> @@ -60,9 +60,9 @@ static inline pgprot_t pte_pgprot(pte_t pte)
>  }
>  
>  #ifndef pmd_page_vaddr
> -static inline unsigned long pmd_page_vaddr(pmd_t pmd)
> +static inline const void *pmd_page_vaddr(pmd_t pmd)
>  {
> -	return ((unsigned long)__va(pmd_val(pmd) & ~PMD_MASKED_BITS));
> +	return (const void *)((unsigned long)__va(pmd_val(pmd) & ~PMD_MASKED_BITS));

This can also just be:

	return __va(pmd_val(pmd) & ~PMD_MASKED_BITS);

I've squashed that in.

cheers