Re: [RFC PATCH 08/21] KVM: TDX: Increase/decrease folio ref for huge pages

[Edgecombe, Rick P]

On Tue, 2025-07-01 at 07:02 -0700, Vishal Annapurve wrote:
> > guest_memfd will have to ensure that pages are unmapped from secure
> > IOMMU pagetables before allowing them to be used by the host.
> > 
> > If secure IOMMU pagetables unmapping fails, I would assume it fails in
> > the similar category of rare "KVM/TDX module/IOMMUFD" bug and I think
> > it makes sense to do the same tdx_buggy_shutdown() with such failures
> > as well.
> 
> In addition we will need a way to fail all further Secure IOMMU table
> walks or some way to stop the active secure DMA by unbinding all the
> TDIs. Maybe such scenarios warrant a BUG_ON() if recovery is not
> possible as possibly any or all of the KVM/IOMMUFD/TDX module can't be
> trusted for reliable functionality anymore.

I mentioned this on another thread. Normal kernel BUG_ON()'s need extreme
justification. As long as the system might survive, they shouldn't be used.