Re: [patch V6 10/14] MDS basics 10

On Wed, 6 Mar 2019, speck for Thomas Gleixner wrote:

> On Wed, 6 Mar 2019, speck for Borislav Petkov wrote:
> > On Fri, Mar 01, 2019 at 10:47:48PM +0100, speck for Thomas Gleixner wrote:
> > > +/* Update the static key controlling the MDS CPU buffer clear in idle */
> > > +static void update_mds_branch_idle(void)
> > > +{
> > > +	/*
> > > +	 * Enable the idle clearing on CPUs which are affected only by
> > > +	 * MDBDS and not any other MDS variant. The other variants cannot
> > > +	 * be mitigated when SMT is enabled,
> > 
> > ... but we're not enabling the key when SMT on those is disabled,
> > AFAICT. Or is that coming later?
> 
> Five lines down ....

Following up on our conversation on IRC, I've reworded the comment:

 	/*
	 * Enable the idle clearing if SMT is active on CPUs which are
	 * affected only by MSBDS and not any other MDS variant.
	 *
	 * The other variants cannot be mitigated when SMT is enabled, so
	 * clearing the buffers on idle just to prevent the Store Buffer
	 * repartitioning leak would be a window dressing exercise.
 	 */
 	if (!boot_cpu_has_bug(X86_BUG_MSBDS_ONLY))
 		return;

Thanks,

	tglx