Re: [RFC PATCH 06/12] KVM: TDX: Return -EIO, not -EINVAL, on a KVM_BUG_ON() condition

[Sean Christopherson <seanjc@google.com>]

On Thu, Aug 28, 2025, Rick P Edgecombe wrote:
> On Thu, 2025-08-28 at 14:00 -0700, Sean Christopherson wrote:
> > But that's not actually what the code does.  The lockdep assert won't trip because
> > KVM never removes S-EPT entries under read-lock:
> 
> Right
> 
> > 
> > 		if (is_mirror_sp(sp)) {
> > 			KVM_BUG_ON(shared, kvm);
> > 			remove_external_spte(kvm, gfn, old_spte, level);
> > 		}
> > 
> > Not because KVM actually guarantees -EBUSY is avoided.  So the current code is
> > flawed, it just doesn't cause problems.
> 
> Flawed, as in the lockdep should assert regardless of EBUSY?

Yep, exactly.

> Seems good to me.
> Probably if we wanted to try to call tdx_sept_remove_private_spte() under read
> lock with special plans to avoid EBUSY we should think twice anyway.

Heh, add a few zeros to "twice" :-D