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

Scott Wood [off-list ref] writes:

On Tue, 2018-05-29 at 15:22 +0000, Diana Madalina Craciun wrote:

quoted

On 05/22/2018 11:31 PM, Scott Wood wrote:

quoted

quoted

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