Re: [PATCH] mm/ptdump: Drop GENERIC_PTDUMP

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

Le 17/12/2024 à 04:48, Anshuman Khandual a écrit :
> GENERIC_PTDUMP does not guard any code but instead just used for platform's
> subscription into core ptdump defined under PTDUMP_CORE, which is selected.
> Instead use PTDUMP_CORE for platform subscription and drop GENERIC_PTDUMP.
> 
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Will Deacon <will@kernel.org>
> Cc: Jonathan Corbet <corbet@lwn.net>
> Cc: Marc Zyngier <maz@kernel.org>
> Cc: Michael Ellerman <mpe@ellerman.id.au>
> Cc: Nicholas Piggin <npiggin@gmail.com>
> Cc: Paul Walmsley <paul.walmsley@sifive.com>
> Cc: Palmer Dabbelt <palmer@dabbelt.com>
> Cc: Heiko Carstens <hca@linux.ibm.com>
> Cc: Vasily Gorbik <gor@linux.ibm.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: linux-arm-kernel@lists.infradead.org
> Cc: linux-doc@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> Cc: kvmarm@lists.linux.dev
> Cc: linuxppc-dev@lists.ozlabs.org
> Cc: linux-riscv@lists.infradead.org
> Cc: linux-s390@vger.kernel.org
> Cc: linux-mm@kvack.org
> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
> ---
> This patch applies on v6.13-rc3 and has been tested on arm64, although it
> also clears build tests on impacted platforms.
> 
>   Documentation/arch/arm64/ptdump.rst       | 1 -
>   arch/arm64/Kconfig                        | 2 +-
>   arch/arm64/kvm/Kconfig                    | 3 +--
>   arch/powerpc/Kconfig                      | 2 +-
>   arch/powerpc/configs/mpc885_ads_defconfig | 1 -
>   arch/riscv/Kconfig                        | 2 +-
>   arch/s390/Kconfig                         | 2 +-
>   arch/x86/Kconfig                          | 2 +-
>   arch/x86/Kconfig.debug                    | 2 +-
>   kernel/configs/debug.config               | 1 -
>   mm/Kconfig.debug                          | 8 ++------
>   11 files changed, 9 insertions(+), 17 deletions(-)
> 

> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index a0ce777f9706..c716f8df10de 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -203,7 +203,7 @@ config PPC
>   	select GENERIC_IRQ_SHOW
>   	select GENERIC_IRQ_SHOW_LEVEL
>   	select GENERIC_PCI_IOMAP		if PCI
> -	select GENERIC_PTDUMP
> +	select PTDUMP_CORE

Please keep alphabetical order.

>   	select GENERIC_SMP_IDLE_THREAD
>   	select GENERIC_TIME_VSYSCALL
>   	select GENERIC_VDSO_TIME_NS

> diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
> index 41a58536531d..b206e5a11f96 100644
> --- a/mm/Kconfig.debug
> +++ b/mm/Kconfig.debug
> @@ -187,7 +187,7 @@ config DEBUG_WX
>   	bool "Warn on W+X mappings at boot"
>   	depends on ARCH_HAS_DEBUG_WX
>   	depends on MMU
> -	select PTDUMP_CORE
> +	depends on PTDUMP_CORE

This change is unclear to me. It works because all arch selecting 
ARCH_HAS_DEBUG_WX also select GENERIC_PTDUMP. For riscv it's even more 
tricking, Riscv only selects GENERIC_PTDUMP when MMU is set, so it works 
because here it also depends on MMU.

But what happens if in the future an architecture selects 
ARCH_HAS_DEBUG_WX without selecting PTDUMP_CORE ?


>   	help
>   	  Generate a warning if any W+X mappings are found at boot.
>   
> @@ -212,9 +212,6 @@ config DEBUG_WX
>   
>   	  If in doubt, say "Y".
>   
> -config GENERIC_PTDUMP
> -	bool
> -
>   config PTDUMP_CORE
>   	bool
>   
> @@ -222,8 +219,7 @@ config PTDUMP_DEBUGFS
>   	bool "Export kernel pagetable layout to userspace via debugfs"
>   	depends on DEBUG_KERNEL
>   	depends on DEBUG_FS
> -	depends on GENERIC_PTDUMP
> -	select PTDUMP_CORE
> +	depends on PTDUMP_CORE
>   	help
>   	  Say Y here if you want to show the kernel pagetable layout in a
>   	  debugfs file. This information is only useful for kernel developers