Re: GPZv4

[Thomas Gleixner <tglx@linutronix.de>]

On Tue, 17 Apr 2018, speck for Konrad Rzeszutek Wilk wrote:
> 2). SBB vs MDD vs SBBD.
> 
> MDD = Memory Disambiguation Disable
> SBB = Speculative Store Bypass
> SBBD = Speculative Store Bypass Disable
> 
> Thomas likes 'MDD', Jon likes 'SBB', but he is also fine with 'SBBD'.

I'm fine with SBBD as well. It's the same semantics as the other knobs as
it controls the mitigation.

> 3). Semantics of SBBD or MDD boot time knob. I followed the way spectre_v2 did it.
> 
> That is this is knob is to disable something and they are:
> 'auto' - follow what the platform recommends. This being linux upstream
>          discussion means following:
> 		on AMD - enable memory disambiguation.
> 		on Intel - no clue. For testing purposes I've left it
>                            as disable memory disambiguation.
> 
> 'off' - ignore what the vendor/distro recommends.
> 'force' - disable it, even if the platform says enable it (like on AMD).

'on' is what spectre_v2 uses.

> And then two more to figure out when to apply the security glue:
> 'boot' or 'userspace'.
> 
> This ties in to 1) - that is if we are not going to provide a 'userspace'
> option then there is no need to even provide the 'boot' option
> so then this sub-discussion becomes moot.
> 
> Thomas (and Linus if you are skulking in the background) - you are the
> top-dog(s) here, can you give the guidance please so I can redo the
> patches on Thursday/Friday?

Linus is not yet lurking. He'll be on the list soon and I'll replay the
discussion to him so he's on the same page.

So can we for now just start with the minimal set of auto, off, on and then
hash out the prctl or not question. The big hammer is the most important
piece we need to have ready for merging when the embargo is lifted.

> P.S.
> I know the AMD secret sauce bits and can do the patches for this, but
> are other folks authorized for this?

Groan. I do not know whether I am or not.

This needs to stop. At some point we need to queue and stage the damned
patches for both Intel and AMD. So AMD should get their act together and
clarify the situation. Borislav can you please reach out to AMD?

Thanks,

	tglx