Re: [RFC v2 14/32] x86/tdx: Handle port I/O

[Andi Kleen]

On Mon, May 10, 2021 at 04:34:34PM -0700, Dan Williams wrote:
> > > Outside the boot decompression code isn't this branch of the "ifdef
> > > BOOT_COMPRESSED_MISC_H"  handled by #VE? I also don't see any usage of
> > > __{in,out}() in this patch.
> >
> > I thought it was all alternative after decompression, so the #VE code
> > shouldn't be called. We still have it for some reason though.
> 
> Right, I'm struggling to understand where these spurious in/out
> instructions are coming from that are not replaced by the
> alternative's code?

There should be nothing in the main tree at least.

> Shouldn't those be dropped on the floor and warned
> about rather than handled? 

It might be related to eventually handling them in ring 3, but
I believe we disallow that currently too and it's not all that useful
anyways.  So yes it could be forbidden.

> I.e. shouldn't port-io instruction escapes
> that would cause #VE be precluded at build-time?

You mean in objtool? That would seem like overkill for a more theoretical
problem.

> > There used to be SAVE_ALL/SAVE_REGS, but they have been all removed in
> > some past refactorings.
> 
> Not a huge deal, but at a minimum it seems a generic construct that
> deserves to be declared centrally rather than tdx-guest-port-io local.

Yes I agree. We should just bring SAVE_ALL/SAVE_REGS back.

-Andi