Re: [PATCH v3 1/6] x86/sme: Use percpu boolean to control wbinvd during kexec

["Huang, Kai" <kai.huang@intel.com>]

(I'll address all wording comments, as always.)

> > Today the first WBINVD in the stop_this_cpu() is performed when SME is
> > *supported* by the platform, and the second WBINVD is done in
> > relocate_kernel() when SME is *activated* by the kernel.  Make things
> > simple by changing to do the second WBINVD when the platform supports
> > SME.  This allows the kernel to simply turn on this percpu boolean when
> > bringing up a CPU by checking whether the platform supports SME.
> 
> Since the race is related to stop_this_cpu() it doesn't affect it. But it does
> mean that the bring up CPU may not flush the cache if takes a kdump kexec before
> the per-cpu var is set? Of course the existing logic doesn't trigger until
> cpuinfo_x86 is populated. What is the consequence?

See another reply.

> 
> Arguably the supported/enabled part could be moved to a separate earlier patch.
> The code change would just get immediately replaced, but the benefit would be
> that a bisect would show which part of the change was responsible.

I am not a fan of splitting the new variable and the user into different
patches, as long as the patch isn't too big to review.  You need to review
them together anyway I think, so arguably putting them together is easier to
review.