Re: [PATCH 4/6] powerpc/64s: Enable barrier_nospec based on firmware settings

[Michael Ellerman]

Michal SuchÃnek <msuchanek@xxxxxxx> writes:
> Hello,
>
> On Tue, 24 Apr 2018 14:15:57 +1000
> Michael Ellerman <mpe@xxxxxxxxxxxxxx> wrote:
>
>> From: Michal Suchanek <msuchanek@xxxxxxx>
>> 
>> Check what firmware told us and enable/disable the barrier_nospec as
>> appropriate.
>> 
>> We err on the side of enabling the barrier, as it's no-op on older
>> systems, see the comment for more detail.
>> 
>> Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
...
>
> I am missing the option for the barrier to be disabled by a kernel
> commandline argument here.
>
> It does make sense to add a kernel parameter that is checked on boot to
> be compatible with other platforms that implement one.

No other platforms have an option to disable variant 1 mitigations, so
there isn't an existing parameter we can use.

Which is not to say we can't add one, but I wasn't sure if it was really
worth it.

But I guess we should add one, I might do it as a follow-up patch.

cheers