Re: x86, microcode: BUG: microcode update that changes x86_capability

[Borislav Petkov <bp@alien8.de>]

On Fri, Sep 19, 2014 at 07:54:14AM -0500, Chuck Ebbert wrote:
> Assuming we can identify all the affected models and steppings, maybe
> something like this would work:
> 
> 1) Refuse to finish booting if a microcode update that disables TSX
> isn't applied before userspace starts running on those CPUs.

Well, I think when we're booting, we would have already applied the
early microcode, no? Because then it is a non-issue.

> 2) Don't allow a late update if TSX is still enabled on those
> processors.

Yeah, so the use case I have in mind is when a long-running machine
wants to apply microcode and this microcode disables CPUID bits and
instructions. And the machine cannot be rebooted.

I guess in that case we would have to issue a warning only on the
affected processors that a rebooted is mandatory and fail the update...
Maybe something like that.

> (1) could be overridden by a command line option for people who want
> to develop TSX code.

The way I understand it, those people shouldn't apply the microcode
patch at all.

-- 
Regards/Gruss,
    Boris.
--