linux-kernel - Re: [PATCH 3/3] mm: Add p{g/4}d_leaf() in asm-generic/pgtable-nop{4/u}d.h

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Message-ID: <Zoa2Qnpzl97hmpHC@x1n>
Date: Thu, 4 Jul 2024 10:48:34 -0400
From: Peter Xu <peterx@...hat.com>
To: Christophe Leroy <christophe.leroy@...roup.eu>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, x86@...nel.org, linux-riscv@...ts.infradead.org,
	Oscar Salvador <osalvador@...e.de>
Subject: Re: [PATCH 3/3] mm: Add p{g/4}d_leaf() in
 asm-generic/pgtable-nop{4/u}d.h

On Thu, Jul 04, 2024 at 08:30:05AM +0200, Christophe Leroy wrote:
> Commit 2c8a81dc0cc5 ("riscv/mm: fix two page table check related
> issues") added pud_leaf() in include/asm-generic/pgtable-nopmd.h
> 
> Do the same for p4d_leaf() and pgd_leaf() to avoid getting them
> erroneously defined by architectures that do not implement the
> related page level.
> 
> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
> ---
>  include/asm-generic/pgtable-nop4d.h | 1 +
>  include/asm-generic/pgtable-nopud.h | 1 +
>  include/linux/pgtable.h             | 6 +++---
>  3 files changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/include/asm-generic/pgtable-nop4d.h b/include/asm-generic/pgtable-nop4d.h
> index 03b7dae47dd4..75c96bbc5a96 100644
> --- a/include/asm-generic/pgtable-nop4d.h
> +++ b/include/asm-generic/pgtable-nop4d.h
> @@ -21,6 +21,7 @@ typedef struct { pgd_t pgd; } p4d_t;
>  static inline int pgd_none(pgd_t pgd)		{ return 0; }
>  static inline int pgd_bad(pgd_t pgd)		{ return 0; }
>  static inline int pgd_present(pgd_t pgd)	{ return 1; }
> +static inline int pgd_leaf(pgd_t pgd)		{ return 0; }
>  static inline void pgd_clear(pgd_t *pgd)	{ }
>  #define p4d_ERROR(p4d)				(pgd_ERROR((p4d).pgd))
>  
> diff --git a/include/asm-generic/pgtable-nopud.h b/include/asm-generic/pgtable-nopud.h
> index eb70c6d7ceff..14aeb8ef2d8a 100644
> --- a/include/asm-generic/pgtable-nopud.h
> +++ b/include/asm-generic/pgtable-nopud.h
> @@ -28,6 +28,7 @@ typedef struct { p4d_t p4d; } pud_t;
>  static inline int p4d_none(p4d_t p4d)		{ return 0; }
>  static inline int p4d_bad(p4d_t p4d)		{ return 0; }
>  static inline int p4d_present(p4d_t p4d)	{ return 1; }
> +static inline int p4d_leaf(p4d_t p4d)		{ return 0; }
>  static inline void p4d_clear(p4d_t *p4d)	{ }
>  #define pud_ERROR(pud)				(p4d_ERROR((pud).p4d))
>  
> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
> index 2a6a3cccfc36..b27e66f542d6 100644
> --- a/include/linux/pgtable.h
> +++ b/include/linux/pgtable.h
> @@ -1882,13 +1882,13 @@ typedef unsigned int pgtbl_mod_mask;
>   * - It should cover all kinds of huge mappings (e.g., pXd_trans_huge(),
>   *   pXd_devmap(), or hugetlb mappings).
>   */
> -#ifndef pgd_leaf
> +#if !defined(__PAGETABLE_P4D_FOLDED) && !defined(pgd_leaf)
>  #define pgd_leaf(x)	false
>  #endif
> -#ifndef p4d_leaf
> +#if !defined(__PAGETABLE_PUD_FOLDED) && !defined(p4d_leaf)
>  #define p4d_leaf(x)	false
>  #endif
> -#ifndef pud_leaf
> +#if !defined(__PAGETABLE_PMD_FOLDED) && !defined(pud_leaf)
>  #define pud_leaf(x)	false
>  #endif
>  #ifndef pmd_leaf

Is it possible to do it the other way round, so that we can still rely on
"ifdef pxx_leaf" to decide whether to provide a fallback, and define them
properly when needed?

IMHO it was a neat way to avoid worrying on any macro defined; it'll be as
simple as "if function xxx not defined, let's define a fallback for xxx".
Per my limited experience it helped a lot on avoid compile issues here and
there..

Thanks,

-- 
Peter Xu