Re: [RFC v1 05/26] x86/traps: Add #VE support for TDX guest

[Andi Kleen]

> Which is supposedly then set up to avoid #VE during the syscall gap,
> yes? Which then results in #VE not having to be IST.

Yes that is currently true because all memory is pre-accepted.

If we ever do lazy accept we would need to make sure the memory accessed in
the syscall gap is already accepted, or move over to an IST.

> > +#ifdef CONFIG_INTEL_TDX_GUEST
> > +DEFINE_IDTENTRY(exc_virtualization_exception)
> > +{
> > +	struct ve_info ve;
> > +	int ret;
> > +
> > +	RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU");
> > +
> > +	/* Consume #VE info before re-enabling interrupts */
> 
> So what happens if NMI happens here, and triggers a nested #VE ?

Yes that's a gap. We should probably bail out and reexecute the original
instruction. The VE handler would need to set a flag for that.

Or alternatively the NMI always gets the VE information and puts
it on some internal stack, but that would seem clunkier.


-Andi