On Wed, May 14, 2025 at 07:06:48AM +0800, Edgecombe, Rick P wrote:
> On Thu, 2025-04-24 at 11:07 +0800, Yan Zhao wrote:
> > +static int split_external_spt(struct kvm *kvm, gfn_t gfn, u64 old_spte,
> > + u64 new_spte, int level)
> > +{
> > + void *external_spt = get_external_spt(gfn, new_spte, level);
> > + int ret;
> > +
> > + KVM_BUG_ON(!external_spt, kvm);
> > +
> > + ret = static_call(kvm_x86_split_external_spt)(kvm, gfn, level, external_spt);
> > + KVM_BUG_ON(ret, kvm);
>
> Shouldn't this BUG_ON be handled in the split_external_spt implementation? I
> don't think we need another one.
Ok. But kvm_x86_split_external_spt() is not for TDX only.
Is it good for KVM MMU core to rely on each implementation to trigger BUG_ON?
> > + return ret;
> > +}
> > /**
> > * handle_removed_pt() - handle a page table removed from the TDP structure
> > *
> > @@ -764,13 +778,13 @@ static u64 tdp_mmu_set_spte(struct kvm *kvm, int as_id, tdp_ptep_t sptep,
> >
> > handle_changed_spte(kvm, as_id, gfn, old_spte, new_spte, level, false);
> >
> > - /*
> > - * Users that do non-atomic setting of PTEs don't operate on mirror
> > - * roots, so don't handle it and bug the VM if it's seen.
> > - */
> > if (is_mirror_sptep(sptep)) {
> > - KVM_BUG_ON(is_shadow_present_pte(new_spte), kvm);
> > - remove_external_spte(kvm, gfn, old_spte, level);
> > + if (!is_shadow_present_pte(new_spte))
> > + remove_external_spte(kvm, gfn, old_spte, level);
> > + else if (is_last_spte(old_spte, level) && !is_last_spte(new_spte, level))
> > + split_external_spt(kvm, gfn, old_spte, new_spte, level);
> > + else
> > + KVM_BUG_ON(1, kvm);
>
> It might be worth a comment what this is looking for at this point. I think it's
> that external EPT only support certain operations, so bug if any unsupported
> operations are seen.
Will do.
> > }
> >
> > return old_spte;
>
