Subject: Re: [PATCH 1/3] x86/cpu: Actually turn off mitigations by default for SPECULATION_MITIGATIONS=n

From: Michael Ellerman <[email-masked]>
Date: Sat, 13 Apr 2024 19:38:47 +1000

Michael Ellerman <[email-masked]> writes:
> Stephen Rothwell <[email-masked]> writes:
...
>> On Tue,  9 Apr 2024 10:51:05 -0700 Sean Christopherson <[email-masked]> 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