[RFC PATCH] powerpc/fsl: Add barrier_nospec implementation for NXP PowerPC Book E

[Michael Ellerman]

Scott Wood <oss at buserror.net> writes:
> On Tue, 2018-05-29 at 15:22 +0000, Diana Madalina Craciun wrote:
>> On 05/22/2018 11:31 PM, Scott Wood wrote:
>
>> > Should there be a way for the user to choose not to enable this (editing
>> > the
>> > device tree doesn't count), for a use case that is not sufficiently
>> > security
>> > sensitive to justify the performance loss?  What is the performance impact
>> > of
>> > this patch?
>> 
>> My reason was that on the other architectures Spectre variant 1
>> mitigations are not disabled either. But I think that it might be a good
>> idea to add a bootarg parameter to disable the barrier.
>
> Is there a specific policy reason why they allow spectre v2 to be disabled but
> not v1,

No.

> or just a matter of not having a mechanism to disable it,

Yes and no. Some of the v1 mitigation is done via masking which can't be
easily patched. eg. array_index_nospec()

> or the parts which could practically be disabled not impacting
> performance much?

That's the mean reason AIUI.

We can add a nospectre_v1 command line option if necessary.

cheers