linux-kernel - Re: [PATCH 3/4] mm: Make GENERIC

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Message-ID: <fc4954d8-3ea6-4542-a5e8-17da2bb9650d@csgroup.eu>
Date: Thu, 13 Feb 2025 08:30:38 +0100
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: Anshuman Khandual <anshuman.khandual@....com>, linux-mm@...ck.org
Cc: steven.price@....com, Paul Walmsley <paul.walmsley@...ive.com>,
 Palmer Dabbelt <palmer@...belt.com>,
 Andrew Morton <akpm@...ux-foundation.org>, linux-riscv@...ts.infradead.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/4] mm: Make GENERIC_PTDUMP dependent on MMU



Le 13/02/2025 à 05:09, Anshuman Khandual a écrit :
> There is no page table dump without a MMU. Make this dependency at generic
> level and drop the same from riscv platform instead.
> 
> Cc: Paul Walmsley <paul.walmsley@...ive.com>
> Cc: Palmer Dabbelt <palmer@...belt.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: linux-riscv@...ts.infradead.org
> Cc: linux-kernel@...r.kernel.org
> Cc: linux-mm@...ck.org
> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
> ---
>   arch/riscv/Kconfig | 2 +-
>   mm/Kconfig.debug   | 1 +
>   2 files changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 7612c52e9b1e..c4cdba6460b8 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -112,7 +112,7 @@ config RISCV
>   	select GENERIC_IRQ_SHOW_LEVEL
>   	select GENERIC_LIB_DEVMEM_IS_ALLOWED
>   	select GENERIC_PCI_IOMAP
> -	select GENERIC_PTDUMP if MMU
> +	select GENERIC_PTDUMP

Are you sure this works as expected ?

See https://docs.kernel.org/kbuild/kconfig-language.html :

Note:
     select should be used with care. select will force a symbol to a 
value without visiting the dependencies. By abusing select you are able 
to select a symbol FOO even if FOO depends on BAR that is not set. In 
general use select only for non-visible symbols (no prompts anywhere) 
and for symbols with no dependencies.

>   	select GENERIC_SCHED_CLOCK
>   	select GENERIC_SMP_IDLE_THREAD
>   	select GENERIC_TIME_VSYSCALL if MMU && 64BIT
> diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
> index a51a1149909a..c08406760d29 100644
> --- a/mm/Kconfig.debug
> +++ b/mm/Kconfig.debug
> @@ -214,6 +214,7 @@ config DEBUG_WX
>   	  If in doubt, say "Y".
>   
>   config GENERIC_PTDUMP
> +	depends on MMU
>   	bool
>   
>   config PTDUMP_CORE