linux-kernel - Re: [PATCH 1/3] x86/cpu: Actually turn off mitigations by default for SPECULATION

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Message-ID: <CAMuHMdWD+UKZAkiUQUJOeRkOoyT4cH1o8=Gu465=K-Ub7O4y9A@mail.gmail.com>
Date: Mon, 15 Apr 2024 13:16:50 +0200
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Michael Ellerman <mpe@...erman.id.au>
Cc: Stephen Rothwell <sfr@...b.auug.org.au>, Sean Christopherson <seanjc@...gle.com>, 
	Jonathan Corbet <corbet@....net>, 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, 
	Peter Zijlstra <peterz@...radead.org>, Josh Poimboeuf <jpoimboe@...nel.org>, linux-doc@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>, 
	Daniel Sneddon <daniel.sneddon@...ux.intel.com>, linuxppc-dev@...ts.ozlabs.org, 
	linux-arch@...r.kernel.org, Catalin Marinas <catalin.marinas@....com>, 
	Will Deacon <will@...nel.org>, Heiko Carstens <hca@...ux.ibm.com>, 
	Linux-Renesas <linux-renesas-soc@...r.kernel.org>
Subject: Re: [PATCH 1/3] x86/cpu: Actually turn off mitigations by default for SPECULATION_MITIGATIONS=n

Hi Michael,

On Sat, Apr 13, 2024 at 11:38 AM Michael Ellerman <mpe@...erman.id.au> wrote:
> Michael Ellerman <mpe@...erman.id.au> writes:
> > Stephen Rothwell <sfr@...b.auug.org.au> writes:
> ...
> >> On Tue,  9 Apr 2024 10:51:05 -0700 Sean Christopherson <seanjc@...gle.com> wrote:
> ...
> >>> diff --git a/kernel/cpu.c b/kernel/cpu.c
> >>> index 8f6affd051f7..07ad53b7f119 100644
> >>> --- a/kernel/cpu.c
> >>> +++ b/kernel/cpu.c
> >>> @@ -3207,7 +3207,8 @@ enum cpu_mitigations {
> >>>  };
> >>>
> >>>  static enum cpu_mitigations cpu_mitigations __ro_after_init =
> >>> -   CPU_MITIGATIONS_AUTO;
> >>> +   IS_ENABLED(CONFIG_SPECULATION_MITIGATIONS) ? CPU_MITIGATIONS_AUTO :
> >>> +                                                CPU_MITIGATIONS_OFF;
> >>>
> >>>  static int __init mitigations_parse_cmdline(char *arg)
> >>>  {
>
> I think a minimal workaround/fix would be:
>
> diff --git a/drivers/base/Kconfig b/drivers/base/Kconfig
> index 2b8fd6bb7da0..290be2f9e909 100644
> --- a/drivers/base/Kconfig
> +++ b/drivers/base/Kconfig
> @@ -191,6 +191,10 @@ config GENERIC_CPU_AUTOPROBE
>  config GENERIC_CPU_VULNERABILITIES
>         bool
>
> +config SPECULATION_MITIGATIONS
> +       def_bool y
> +       depends on !X86
> +
>  config SOC_BUS
>         bool
>         select GLOB

Thanks, that works for me (on arm64), so
Tested-by: Geert Uytterhoeven <geert+renesas@...der.be>

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68korg

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds