Re: ***UNCHECKED*** Re: Re: Re: [PATCH v5 08/11] TAAv5 8

On Wed, 16 Oct 2019, speck for Michal Hocko wrote:
> On Wed 16-10-19 09:54:34, speck for Michal Hocko wrote:
> [...]
> > +config X86_INTEL_TSX_MODE_OFF
> > +	bool "off"
> > +	help
> > +	  TSX is always disabled - equals tsx=off command line parameter.
> > +
> > +config X86_INTEL_TSX_MODE_ON
> > +	bool "on"
> > +	help
> > +	  TSX is always enabled on TSX capable HW - equals tsx=on command line
> > +	  parameter.
> > +
> > +config X86_INTEL_TSX_MODE_AUTO
> > +	bool "auto"
> > +	help
> > +	  TSX is enabled on TSX capable HW that is believed to be safe against
> > +	  side channel attacks- equals tsx=auto command line parameter.
> > +endchoice
> 
> I have just reread the discussion again and I have to say that there is
> more confusion and uncertainty than I would like to see. Can somebody
> from Intel give an authoritative answer to the following question
> please?
> 
> Is tsx=auto going to lead to any different state than tsx=on? In other
> words does auto mode make any sense at all?

Is it only my vacation induced spark of mental sanity or is this whole TAA
thing a complete trainwreck again?

We're at version 5 and more than 3 month since the first RFC got posted and
we are still debating which CPUs are affected and which migitations are
going to be deployed depending on the CPU advertized misfeatures and the
eventually surfacing microcode?

Can we please stop this complete waste of time right now and start over
with clarifying the situation? I.e. someone at Intel needs to sit down and
write up a matrix:

TAA-Affected | MDS_NO | VERW works | TSX_MSR | Resulting action
-------------|--------|------------|---------|-----------------
 No          |   X    |     X      |    Y    | ?
 No          |   X    |     X      |    N    | None
 Yes         |   0    |     0      |    0    | SNAFU
 ...         |        |            |         |

You surely can fill in the rest on your own, right?

And exactly that information wants to be in the admin documentation or in a
separate Documentation/x86/taa.rst as well.

Thanks,

	tglx