linux-kernel - Re: [PATCH 5/6] mm: Kconfig: make config SECRETMEM visible with EXPERT

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Date:   Thu, 8 Sep 2022 14:24:15 +0300
From:   Mike Rapoport <rppt@...ux.ibm.com>
To:     Lukas Bulwahn <lukas.bulwahn@...il.com>
Cc:     Russell King <linux@...linux.org.uk>,
        linux-arm-kernel@...ts.infradead.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media@...r.kernel.org, Peter Chen <peter.chen@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        Masahiro Yamada <masahiroy@...nel.org>,
        linux-kbuild@...r.kernel.org, kernel-janitors@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/6] mm: Kconfig: make config SECRETMEM visible with
 EXPERT

On Thu, Sep 08, 2022 at 12:43:36PM +0200, Lukas Bulwahn wrote:
> Commit 6a108a14fa35 ("kconfig: rename CONFIG_EMBEDDED to CONFIG_EXPERT")
> introduces CONFIG_EXPERT to carry the previous intent of CONFIG_EMBEDDED
> and just gives that intent a much better name. That has been clearly a good
> and long overdue renaming, and it is clearly an improvement to the kernel
> build configuration that has shown to help managing the kernel build
> configuration in the last decade.
> 
> However, rather than bravely and radically just deleting CONFIG_EMBEDDED,
> this commit gives CONFIG_EMBEDDED a new intended semantics, but keeps it
> open for future contributors to implement that intended semantics:
> 
>     A new CONFIG_EMBEDDED option is added that automatically selects
>     CONFIG_EXPERT when enabled and can be used in the future to isolate
>     options that should only be considered for embedded systems (RISC
>     architectures, SLOB, etc).
> 
> Since then, this CONFIG_EMBEDDED implicitly had two purposes:
> 
>   - It can make even more options visible beyond what CONFIG_EXPERT makes
>     visible. In other words, it may introduce another level of enabling the
>     visibility of configuration options: always visible, visible with
>     CONFIG_EXPERT and visible with CONFIG_EMBEDDED.
> 
>   - Set certain default values of some configurations differently,
>     following the assumption that configuring a kernel build for an
>     embedded system generally starts with a different set of default values
>     compared to kernel builds for all other kind of systems.
> 
> Considering the second purpose, note that already probably arguing that a
> kernel build for an embedded system would choose some values differently is
> already tricky: the set of embedded systems with Linux kernels is already
> quite diverse. Many embedded system have powerful CPUs and it would not be
> clear that all embedded systems just optimize towards one specific aspect,
> e.g., a smaller kernel image size. So, it is unclear if starting with "one
> set of default configuration" that is induced by CONFIG_EMBEDDED is a good
> offer for developers configuring their kernels.
> 
> Also, the differences of needed user-space features in an embedded system
> compared to a non-embedded system are probably difficult or even impossible
> to name in some generic way.
> 
> So it is not surprising that in the last decade hardly anyone has
> contributed changes to make something default differently in case of
> CONFIG_EMBEDDED=y.
> 
> Currently, in v6.0-rc4, SECRETMEM is the only config switched off if
> CONFIG_EMBEDDED=y.
> 
> As long as that is actually the only option that currently is selected or
> deselected, it is better to just make SECRETMEM configurable at build time
> by experts using menuconfig instead.
> 
> Make SECRETMEM configurable when EXPERT is set and otherwise default to
> yes. Further, SECRETMEM needs ARCH_HAS_SET_DIRECT_MAP.
> 
> This allows us to remove CONFIG_EMBEDDED in the close future.
> 
> Signed-off-by: Lukas Bulwahn <lukas.bulwahn@...il.com>

Acked-by: Mike Rapoport <rppt@...ux.ibm.com>

> ---
>  mm/Kconfig | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/Kconfig b/mm/Kconfig
> index ceec438c0741..aa154c20b129 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -1068,7 +1068,13 @@ config IO_MAPPING
>  	bool
>  
>  config SECRETMEM
> -	def_bool ARCH_HAS_SET_DIRECT_MAP && !EMBEDDED
> +	default y
> +	bool "Enable memfd_secret() system call" if EXPERT
> +	depends on ARCH_HAS_SET_DIRECT_MAP
> +	help
> +	  Enable the memfd_secret() system call with the ability to create
> +	  memory areas visible only in the context of the owning process and
> +	  not mapped to other processes and other kernel page tables.
>  
>  config ANON_VMA_NAME
>  	bool "Anonymous VMA name support"
> -- 
> 2.17.1
> 

-- 
Sincerely yours,
Mike.