Re: [PATCH v12 07/22] x86/virt/tdx: Add skeleton to enable TDX on demand

[Peter Zijlstra]

On Fri, Jun 30, 2023 at 09:55:32AM +0000, Huang, Kai wrote:
> On Fri, 2023-06-30 at 11:26 +0200, Peter Zijlstra wrote:
> > On Thu, Jun 29, 2023 at 12:10:00AM +0000, Huang, Kai wrote:
> > > On Wed, 2023-06-28 at 15:17 +0200, Peter Zijlstra wrote:
> > > > On Tue, Jun 27, 2023 at 02:12:37AM +1200, Kai Huang wrote:
> > > > > +EXPORT_SYMBOL_GPL(tdx_cpu_enable);
> > > > 
> > > > I can't find a single caller of this.. why is this exported?
> > > 
> > > It's for KVM TDX patch to use, which isn't in this series.
> > > 
> > > I'll remove the export.  KVM TDX series can export it.
> > 
> > Fair enough; where will the KVM TDX series call this? Earlier there was
> > talk about doing it at kvm module load time -- but I objected (and still
> > do object) to that.
> > 
> > What's the current plan?
> > 
> 
> The direction is still doing it during module load (not my series anyway).  But
> this can be a separate discussion with KVM maintainers involved.

They all on Cc afaict.

> I understand you have concern that you don't want to have the memory & cpu time
> wasted on enabling TDX by default.  For that we can have a kernel command line
> to disable TDX once for all (we can even make it default).

That's insane, I don't want to totally disable it. I want it done at
guard creation. Do the whole TDX setup the moment you actually create a
TDX guast.

Totally killing TDX is stupid, just about as stupid as doing it on
module load (which equates to always doing it).

> Also, KVM will have a module parameter 'enable_tdx'.  I am hoping this could
> reduce your concern too.

I don't get this obsession with doing at module load time :/