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From: Michael Ellerman <mpe@ellerman.id.au>
To: Stephen Rothwell <sfr@canb.auug.org.au>, Sean Christopherson
 <seanjc@google.com>
Cc: Jonathan Corbet <corbet@lwn.net>, 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, Peter Zijlstra
 <peterz@infradead.org>, Josh Poimboeuf <jpoimboe@kernel.org>,
 linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, Pawan Gupta
 <pawan.kumar.gupta@linux.intel.com>, Daniel Sneddon
 <daniel.sneddon@linux.intel.com>, linuxppc-dev@lists.ozlabs.org,
 linux-arch@vger.kernel.org, Catalin Marinas <catalin.marinas@arm.com>,
 Will Deacon <will@kernel.org>, Heiko Carstens <hca@linux.ibm.com>
Subject: Re: [PATCH 1/3] x86/cpu: Actually turn off mitigations by default
 for SPECULATION_MITIGATIONS=n
In-Reply-To: <87edb9d33r.fsf@mail.lhotse>
References: <20240409175108.1512861-1-seanjc@google.com>
 <20240409175108.1512861-2-seanjc@google.com>
 <20240413115324.53303a68@canb.auug.org.au> <87edb9d33r.fsf@mail.lhotse>
Date: Sat, 13 Apr 2024 19:38:47 +1000
Message-ID: <87bk6dd2l4.fsf@mail.lhotse>
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Michael Ellerman <mpe@ellerman.id.au> writes:
> Stephen Rothwell <sfr@canb.auug.org.au> writes:
..
>> On Tue,  9 Apr 2024 10:51:05 -0700 Sean Christopherson <seanjc@google.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

cheers