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

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Message-ID: <20240415084250.7b00ea63@canb.auug.org.au>
Date: Mon, 15 Apr 2024 08:42:50 +1000
From: Stephen Rothwell <sfr@...b.auug.org.au>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Michael Ellerman <mpe@...erman.id.au>, 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>
Subject: Re: [PATCH 1/3] x86/cpu: Actually turn off mitigations by default
 for SPECULATION_MITIGATIONS=n

Hi all,

On Sat, 13 Apr 2024 19:38:47 +1000 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

The original commit is now in Linus' tree.

-- 
Cheers,
Stephen Rothwell

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