Re: [patch V5 09/14] MDS basics 9

On Fri, 1 Mar 2019, speck for Josh Poimboeuf wrote:
> On Fri, Mar 01, 2019 at 10:40:22AM -0600, Josh Poimboeuf wrote:
> > On Fri, Mar 01, 2019 at 05:03:39PM +0100, speck for Thomas Gleixner wrote:
> > > On Fri, 1 Mar 2019, speck for Josh Poimboeuf wrote:
> > > > Andrea brought up a good question privately -- this patch mitigates
> > > > MSBDS for HT, but HT will still be susceptible to the other two MDS
> > > > issues.  So what's the point?  It seems this patch only protects people
> > > > who don't care about MDS in the first place.
> > > 
> > > Indeed for most CPU models it's pointless.
> > > 
> > > The ones which are only affected by MSBDS are Atom Silvermont/Airmont which
> > > are all single threaded and the XEON PHIs.
> > > 
> > > For XEON PHI it actually makes sense because XEON PHI does not have L1TF
> > > either.
> > > 
> > > But yes, for everything else it's just window dressing.
> > 
> > Makes sense.  I didn't realize that some CPUs were affected by MSBDS and
> > not other MDSes.
> > 
> > Can you add that justification to the documentation and/or patch
> > description?
> 
> Or even better, can we only do the idle clearing on XEON PHI?
> 
> Also it sounds like the mds vulnerabilities file shouldn't ever show
> "SMT vulnerable" for XEON PHI.

Yeah.

So I was looking at that table again and found the following stepping
related info:

06_8EH,06_9EH	<=B	Kaby/Coffe Lake		Yes Yes Yes Yes
06_9E		0xC	Coffee Lake		No  Yes Yes Yes
06_8E		0xB	Whiskey Lake(ULT)	No  Yes	Yes Yes

06_8E		0xC	Whiskey L (ULT refresh) No  No  No  No
06_9E		0xD	Whiskey Lake (Deskto)   No  No  No  No


06_55H		5	Cascade Lake		No  Yes Yes Yes

06_55H		6	Cascade Lake		No  No  No  No

Will these 'fixed' steppings have MDS_NO set?

Thanks,

	tglx