Re: [PATCH v2 1/2] arch/Kconfig: Make CONFIG_CPU_SPECTRE available for all architectures

From: Mark Rutland <mark.rutland@arm.com>
To: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Cc: "Russell King" <linux@armlinux.org.uk>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Ingo Molnar" <mingo@redhat.com>,
	"Borislav Petkov" <bp@alien8.de>,
	"Dave Hansen" <dave.hansen@linux.intel.com>,
	x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
	"Kees Cook" <keescook@chromium.org>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Masahiro Yamada" <masahiroy@kernel.org>,
	"Peter Zijlstra (Intel)" <peterz@infradead.org>,
	"Sami Tolvanen" <samitolvanen@google.com>,
	"Colin Ian King" <colin.king@canonical.com>,
	"Frederic Weisbecker" <frederic@kernel.org>,
	"Mike Rapoport" <rppt@kernel.org>,
	"YiFei Zhu" <yifeifz2@illinois.edu>,
	"Steven Rostedt (VMware)" <rostedt@goodmis.org>,
	"Viresh Kumar" <viresh.kumar@linaro.org>,
	"Andrey Konovalov" <andreyknvl@gmail.com>,
	"Wang Kefeng" <wangkefeng.wang@huawei.com>,
	"Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>,
	"Nathan Chancellor" <nathan@kernel.org>,
	"Nick Desaulniers" <ndesaulniers@google.com>,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v2 1/2] arch/Kconfig: Make CONFIG_CPU_SPECTRE available for all architectures
Date: Thu, 28 Oct 2021 14:49:18 +0100	[thread overview]
Message-ID: <20211028134918.GB48435@lakrids.cambridge.arm.com> (raw)
In-Reply-To: <232b692cd79e4f6e4c3ee7055b5f02792a28d2c4.1635383031.git.pawan.kumar.gupta@linux.intel.com>

On Wed, Oct 27, 2021 at 06:33:22PM -0700, Pawan Gupta wrote:
> Borrow CONFIG_CPU_SPECTRE from ARM to be available for all
> architectures. This will help in configuration of features that depend
> on CPU being affected by spectre class of vulnerabilities.
> 
> Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>

Given that spectre isn't one specific issue, biut rather a blanket term
for a bunch of things that can have variable overlap, I don't think this
makes much sense unless we're going to add finer-grained options for all
the variants, and IMO it'd make more sene for the architectures to
directly select the things that'd otherwise be dependent on this.

Thanks,
Mark.

> ---
>  arch/Kconfig        | 3 +++
>  arch/arm/mm/Kconfig | 3 ---
>  arch/x86/Kconfig    | 1 +
>  3 files changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/Kconfig b/arch/Kconfig
> index 8df1c7102643..6aa856d51cb7 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -1091,6 +1091,9 @@ config ARCH_SUPPORTS_RT
>  config CPU_NO_EFFICIENT_FFS
>  	def_bool n
>  
> +config CPU_SPECTRE
> +	bool
> +
>  config HAVE_ARCH_VMAP_STACK
>  	def_bool n
>  	help
> diff --git a/arch/arm/mm/Kconfig b/arch/arm/mm/Kconfig
> index 8355c3895894..44551465fd03 100644
> --- a/arch/arm/mm/Kconfig
> +++ b/arch/arm/mm/Kconfig
> @@ -828,9 +828,6 @@ config CPU_BPREDICT_DISABLE
>  	help
>  	  Say Y here to disable branch prediction.  If unsure, say N.
>  
> -config CPU_SPECTRE
> -	bool
> -
>  config HARDEN_BRANCH_PREDICTOR
>  	bool "Harden the branch predictor against aliasing attacks" if EXPERT
>  	depends on CPU_SPECTRE
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index d9830e7e1060..769739da67c6 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -124,6 +124,7 @@ config X86
>  	select CLKEVT_I8253
>  	select CLOCKSOURCE_VALIDATE_LAST_CYCLE
>  	select CLOCKSOURCE_WATCHDOG
> +	select CPU_SPECTRE
>  	select DCACHE_WORD_ACCESS
>  	select EDAC_ATOMIC_SCRUB
>  	select EDAC_SUPPORT
> -- 
> 2.31.1
> 