Re: [PATCH 1/2] cpu: Re-enable CPU mitigations by default for !X86 architectures

[Michael Ellerman]

Josh Poimboeuf <jpoimboe@xxxxxxxxxx> writes:
> On Tue, Apr 16, 2024 at 05:15:06PM -0700, Sean Christopherson wrote:
>> Add a generic Kconfig, CPU_MITIGATIONS, to control whether or not CPU
>> mitigations are enabled by default, and force it on for all architectures
>> except x86.  A recent commit to turn mitigations off by default if
>> SPECULATION_MITIGATIONS=n kinda sorta missed that "cpu_mitigations" is
>> completely generic, where as SPECULATION_MITIGATIONS is x86 specific.
>> 
>> Alternatively, SPECULATION_MITIGATIONS could simply be defined in common
>> code, but that creates weirdness for x86 because SPECULATION_MITIGATIONS
>> ends up being defined twice, and the default behavior would likely depend
>> on the arbitrary include order (if the two definitions diverged).
>> 
>> Ideally, CPU_MITIGATIONS would be unconditionally on by default for all
>> architectures, and manually turned off, but there is no way to unselect a
>> Kconfig.
>> 
>> Reported-by: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>
>> Reported-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
>> Reported-by: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
>> Closes: https://lkml.kernel.org/r/20240413115324.53303a68%40canb.auug.org.au
>> Fixes: f337a6a21e2f ("x86/cpu: Actually turn off mitigations by default for SPECULATION_MITIGATIONS=n")
>> Cc: stable@xxxxxxxxxxxxxxx
>> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
>
> It seems confusing to have two config options which have very similar
> names and similar purposes (with subtle differences depending on the
> arch).

I agree.

But can we please get Sean's fix into mainline before rc5.

cheers