[MODERATED] Re: [PATCH 3/4] V7 more sampling fun 3

[Josh Poimboeuf <jpoimboe@redhat.com>]

On Tue, Apr 14, 2020 at 02:03:02PM -0700, speck for mark gross wrote:
> > > +	[SRBDS_MITIGATION_NOT_AFFECTED_TSX_OFF]	= "Not affected (TSX disabled)",
> > 
> > The CPU *is* affected, it just happens to be mitigated, right?
> This depends on perspective.
> The only mitigation to SRBS is for the uCode to serialize access to the off
> core hwRNG and to do a ghost transfer of a through away random number such that
> if it leaks you don't get the right random number.  I think there may be some
> buffer clearing in there too.
> 
> Disabling TSX from that point of view is not mitigating the issue so much as
> hiding exposure to it.
> 
> I can see it either way.  Not sure which is better.  After reading my logic do
> you still think it would make more sence to change "Not affected (TSX
> disabled)" to "Mitigated: TSX disabled"?

From a user's perspective, "hiding exposure" is the same as a
mitigation.  So I think it makes sense to call it a mitigation.

> > > +		 */
> > > +		if ((ia32_cap & ARCH_CAP_MDS_NO) &&
> > > +		    !((ia32_cap & ARCH_CAP_TSX_CTRL_MSR) ||
> > > +		      cpu_has(c, X86_FEATURE_RTM)))
> > > +			goto srbds_not_affected;
> > > +
> > > +		setup_force_cpu_bug(X86_BUG_SRBDS);
> > > +	}
> > > +srbds_not_affected:
> > > +
> > >  	if (cpu_matches(NO_MELTDOWN, cpu_vuln_whitelist))
> > >  		return;
> > 
> > I'm thinking it would be more readable to have the newline between the
> > bracket and the 'if', instead of between the label and the 'if'.
> so, lose the newline between the label and the if?

Yes, and add one between the '}' and the label.

-- 
Josh