Re: [PATCH v2 5/8] x86/speculation: Add basic support for IBPB

[David Woodhouse]

On Sun, 2018-01-21 at 20:01 +0100, Borislav Petkov wrote:
> 
> so execution runs directly into the MSR write and the JMP is gone.
> 
> So I don't see indirect branches anywhere...

Wait until the wind changes.

Congratulations, you've just turned a potential GCC missed optimisation
into a kernel bug. We don't *care* that it's unlikely that GCC will
miss that optimisation. The point is that it doesn't *have* to do it,
and we don't *check*.

cf.Âhttps://lkml.org/lkml/2018/1/12/176


... after which Peter went off and implemented that check, which is all
fine and dandy but let's not rely on backporting that too.

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