[MODERATED] Re: [PATCH v5 08/11] TAAv5 8

[Ben Hutchings <ben@decadent.org.uk>]

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On Tue, 2019-10-15 at 18:12 -0500, speck for Josh Poimboeuf wrote:
> On Tue, Oct 15, 2019 at 11:14:03PM +0200, speck for Jiri Kosina wrote:
[...]
> > OK, that piece of information finally made it to make sense again :)
> > 
> > So I believe distros still want the option (Michal's patch) to default to 
> > 'auto', so that actual heavy users of TSX will get the right thing once 
> > they update their CPUs to !TAA_BUG ones, but it's less urgent that I 
> > originally thought.
> 
> So if I understand correctly, you're postulating that distros want:
> 
> a) TAA_BUG && MDS_NO=0 => TSX on
> b) TAA_BUG && MDS_NO=1 => TSX off
> c) !TAA_BUG            => TSX on
[...]

I think this should be:

a) TAA_BUG && MD_CLEAR=1 => TSX on
b) TAA_BUG && MD_CLEAR=0 => TSX off
c) !TAA_BUG              => TSX on

As I understand it, with currently released microcode, no CPUs have
both MDS_NO and MD_CLEAR set.  But with the pending microcode updates,
CPUs with MDS_NO=1 will also get MD_CLEAR=1 and we can use VERW to
mitigate against TAA.

Ben.

-- 
Ben Hutchings
It's easier to fight for one's principles than to live up to them.


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