Re: [PATCH 1/4] arch: consolidate existing CONFIG_PAGE_SIZE_*KB definitions

[Christophe Leroy <christophe.leroy@csgroup.eu>]

Le 26/02/2024 à 17:14, Arnd Bergmann a écrit :
> From: Arnd Bergmann <arnd@arndb.de>
> 
> These four architectures define the same Kconfig symbols for configuring
> the page size. Move the logic into a common place where it can be shared
> with all other architectures.
> 
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>   arch/Kconfig                      | 58 +++++++++++++++++++++++++++++--
>   arch/hexagon/Kconfig              | 25 +++----------
>   arch/hexagon/include/asm/page.h   |  6 +---
>   arch/loongarch/Kconfig            | 21 ++++-------
>   arch/loongarch/include/asm/page.h | 10 +-----
>   arch/mips/Kconfig                 | 58 +++----------------------------
>   arch/mips/include/asm/page.h      | 16 +--------
>   arch/sh/include/asm/page.h        | 13 +------
>   arch/sh/mm/Kconfig                | 42 +++++++---------------
>   9 files changed, 88 insertions(+), 161 deletions(-)
> 
> diff --git a/arch/Kconfig b/arch/Kconfig
> index a5af0edd3eb8..237cea01ed9b 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -1078,17 +1078,71 @@ config HAVE_ARCH_COMPAT_MMAP_BASES
>   	  and vice-versa 32-bit applications to call 64-bit mmap().
>   	  Required for applications doing different bitness syscalls.
>   
> +config HAVE_PAGE_SIZE_4KB
> +	bool
> +
> +config HAVE_PAGE_SIZE_8KB
> +	bool
> +
> +config HAVE_PAGE_SIZE_16KB
> +	bool
> +
> +config HAVE_PAGE_SIZE_32KB
> +	bool
> +
> +config HAVE_PAGE_SIZE_64KB
> +	bool
> +
> +config HAVE_PAGE_SIZE_256KB
> +	bool
> +
> +choice
> +	prompt "MMU page size"
> +

That's a nice re-factor.

The only drawback I see is that we are loosing several interesting 
arch-specific comments/help text. Don't know if there could be an easy 
way to keep them.


> +config PAGE_SIZE_4KB
> +	bool "4KB pages"
> +	depends on HAVE_PAGE_SIZE_4KB
> +
> +config PAGE_SIZE_8KB
> +	bool "8KB pages"
> +	depends on HAVE_PAGE_SIZE_8KB
> +
> +config PAGE_SIZE_16KB
> +	bool "16KB pages"
> +	depends on HAVE_PAGE_SIZE_16KB
> +
> +config PAGE_SIZE_32KB
> +	bool "32KB pages"
> +	depends on HAVE_PAGE_SIZE_32KB
> +
> +config PAGE_SIZE_64KB
> +	bool "64KB pages"
> +	depends on HAVE_PAGE_SIZE_64KB
> +
> +config PAGE_SIZE_256KB
> +	bool "256KB pages"
> +	depends on HAVE_PAGE_SIZE_256KB

Hexagon seem to also use CONFIG_PAGE_SIZE_1MB ?

> +
> +endchoice
> +
>   config PAGE_SIZE_LESS_THAN_64KB
>   	def_bool y
> -	depends on !ARM64_64K_PAGES
>   	depends on !PAGE_SIZE_64KB
> -	depends on !PARISC_PAGE_SIZE_64KB
>   	depends on PAGE_SIZE_LESS_THAN_256KB
>   
>   config PAGE_SIZE_LESS_THAN_256KB
>   	def_bool y
>   	depends on !PAGE_SIZE_256KB
>   
> +config PAGE_SHIFT
> +	int
> +	default 12 if PAGE_SIZE_4KB
> +	default 13 if PAGE_SIZE_8KB
> +	default 14 if PAGE_SIZE_16KB
> +	default 15 if PAGE_SIZE_32KB
> +	default 16 if PAGE_SIZE_64KB
> +	default 18 if PAGE_SIZE_256KB
> +
>   # This allows to use a set of generic functions to determine mmap base
>   # address by giving priority to top-down scheme only if the process
>   # is not in legacy mode (compat task, unlimited stack size or
> diff --git a/arch/hexagon/Kconfig b/arch/hexagon/Kconfig
> index a880ee067d2e..aac46ee1a000 100644
> --- a/arch/hexagon/Kconfig
> +++ b/arch/hexagon/Kconfig
> @@ -8,6 +8,11 @@ config HEXAGON
>   	select ARCH_HAS_SYNC_DMA_FOR_DEVICE
>   	select ARCH_NO_PREEMPT
>   	select DMA_GLOBAL_POOL
> +	select FRAME_POINTER
> +	select HAVE_PAGE_SIZE_4KB
> +	select HAVE_PAGE_SIZE_16KB
> +	select HAVE_PAGE_SIZE_64KB
> +	select HAVE_PAGE_SIZE_256KB
>   	# Other pending projects/to-do items.
>   	# select HAVE_REGS_AND_STACK_ACCESS_API
>   	# select HAVE_HW_BREAKPOINT if PERF_EVENTS
> @@ -120,26 +125,6 @@ config NR_CPUS
>   	  This is purely to save memory - each supported CPU adds
>   	  approximately eight kilobytes to the kernel image.
>   
> -choice
> -	prompt "Kernel page size"
> -	default PAGE_SIZE_4KB
> -	help
> -	  Changes the default page size; use with caution.
> -
> -config PAGE_SIZE_4KB
> -	bool "4KB"
> -
> -config PAGE_SIZE_16KB
> -	bool "16KB"
> -
> -config PAGE_SIZE_64KB
> -	bool "64KB"
> -
> -config PAGE_SIZE_256KB
> -	bool "256KB"
> -
> -endchoice
> -
>   source "kernel/Kconfig.hz"
>   
>   endmenu
> diff --git a/arch/hexagon/include/asm/page.h b/arch/hexagon/include/asm/page.h
> index 10f1bc07423c..65c9bac639fa 100644
> --- a/arch/hexagon/include/asm/page.h
> +++ b/arch/hexagon/include/asm/page.h
> @@ -13,27 +13,22 @@
>   /*  This is probably not the most graceful way to handle this.  */
>   
>   #ifdef CONFIG_PAGE_SIZE_4KB
> -#define PAGE_SHIFT 12
>   #define HEXAGON_L1_PTE_SIZE __HVM_PDE_S_4KB
>   #endif
>   
>   #ifdef CONFIG_PAGE_SIZE_16KB
> -#define PAGE_SHIFT 14
>   #define HEXAGON_L1_PTE_SIZE __HVM_PDE_S_16KB
>   #endif
>   
>   #ifdef CONFIG_PAGE_SIZE_64KB
> -#define PAGE_SHIFT 16
>   #define HEXAGON_L1_PTE_SIZE __HVM_PDE_S_64KB
>   #endif
>   
>   #ifdef CONFIG_PAGE_SIZE_256KB
> -#define PAGE_SHIFT 18
>   #define HEXAGON_L1_PTE_SIZE __HVM_PDE_S_256KB
>   #endif
>   
>   #ifdef CONFIG_PAGE_SIZE_1MB
> -#define PAGE_SHIFT 20
>   #define HEXAGON_L1_PTE_SIZE __HVM_PDE_S_1MB
>   #endif
>   
> @@ -50,6 +45,7 @@
>   #define HVM_HUGEPAGE_SIZE 0x5
>   #endif
>   
> +#define PAGE_SHIFT CONFIG_PAGE_SHIFT
>   #define PAGE_SIZE  (1UL << PAGE_SHIFT)
>   #define PAGE_MASK  (~((1 << PAGE_SHIFT) - 1))
>   

Could we move PAGE_SIZE and PAGE_MASK in a generic/core header instead 
of having it duplicated for each arch ?

Christophe