Re: [PATCH v2 22/24] KVM: TDX: Finalize VM initialization

[Yan Zhao <yan.y.zhao@intel.com>]

On Tue, Jan 07, 2025 at 03:02:28PM +0100, Paolo Bonzini wrote:
> On Tue, Jan 7, 2025 at 8:45 AM Yan Zhao <yan.y.zhao@intel.com> wrote:
> > > @@ -1715,8 +1715,8 @@ static int tdx_gmem_post_populate(struct kvm *kvm, gfn_t gfn, kvm_pfn_t pfn,
> > >               goto out;
> > >       }
> > > -     WARN_ON_ONCE(!atomic64_read(&kvm_tdx->nr_premapped));
> > > -     atomic64_dec(&kvm_tdx->nr_premapped);
> > > +     if (!WARN_ON_ONCE(!atomic64_read(&kvm_tdx->nr_premapped)))
> > > +             atomic64_dec(&kvm_tdx->nr_premapped);
> > One concern here.
> > If tdx_gmem_post_populate() is called when kvm_tdx->nr_premapped is 0, it will
> > trigger the WARN_ON here, indicating that something has gone wrong.
> > Should KVM refuse to start the TD in this case?
> >
> > If we don't decrease kvm_tdx->nr_premapped in that case, it will remain 0,
> > allowing it to pass the check in tdx_td_finalize().
> 
> Let's make it a KVM_BUG_ON then.

Ok. Fair enough.