On Fri, 2024-06-07 at 12:10 +0200, Paolo Bonzini wrote:
> On Thu, May 30, 2024 at 11:07 PM Rick Edgecombe
> <rick.p.edgecombe@xxxxxxxxx> wrote:
> > + /* Update mirrored mapping with page table link */
> > + int (*reflect_link_spt)(struct kvm *kvm, gfn_t gfn, enum pg_level
> > level,
> > + void *mirrored_spt);
> > + /* Update the mirrored page table from spte getting set */
> > + int (*reflect_set_spte)(struct kvm *kvm, gfn_t gfn, enum pg_level
> > level,
> > + kvm_pfn_t pfn);
>
> Possibly link_external_spt and set_external_spte, since you'll have to
> s/mirrored/external/ in the comment. But not a hard request.
Definitely seems better now that we have the "external" nomenclature.
>
> > +static void *get_mirrored_spt(gfn_t gfn, u64 new_spte, int level)
> > +{
> > + if (is_shadow_present_pte(new_spte) && !is_last_spte(new_spte,
> > level)) {
> > + struct kvm_mmu_page *sp =
> > to_shadow_page(pfn_to_hpa(spte_to_pfn(new_spte)));
>
> I think this is spte_to_child_sp(new_spte)?
Yes, that seems much easier than all this.
[snip]
>
> > +static int __must_check reflect_set_spte_present(struct kvm *kvm,
> > tdp_ptep_t sptep,
>
> tdp_mmu_set_mirror_spte_atomic?
>
> > + /*
> > + * For mirrored page table, callbacks are needed to propagate SPTE
> > + * change into the mirrored page table. In order to atomically
> > update
> > + * both the SPTE and the mirrored page tables with callbacks,
> > utilize
> > + * freezing SPTE.
> > + * - Freeze the SPTE. Set entry to REMOVED_SPTE.
> > + * - Trigger callbacks for mirrored page tables.
> > + * - Unfreeze the SPTE. Set the entry to new_spte.
> > + */
>
> /*
> * We need to lock out other updates to the SPTE until the external
> * page table has been modified. Use REMOVED_SPTE similar to
> * the zapping case.
> */
>
> Easy peasy. :) We may want to rename REMOVED_SPTE to FROZEN_SPTE; feel
> free to do it at the head of this series, then it can be picked for
> 6.11.
Ok.
>
> > -static inline int __tdp_mmu_set_spte_atomic(struct tdp_iter *iter, u64
> > new_spte)
> > +static inline int __tdp_mmu_set_spte_atomic(struct kvm *kvm, struct
> > tdp_iter *iter, u64 new_spte)
> > {
> > u64 *sptep = rcu_dereference(iter->sptep);
> >
> > @@ -571,15 +629,36 @@ static inline int __tdp_mmu_set_spte_atomic(struct
> > tdp_iter *iter, u64 new_spte)
> > */
> > WARN_ON_ONCE(iter->yielded || is_removed_spte(iter->old_spte));
> >
> > - /*
> > - * Note, fast_pf_fix_direct_spte() can also modify TDP MMU SPTEs and
> > - * does not hold the mmu_lock. On failure, i.e. if a different
> > logical
> > - * CPU modified the SPTE, try_cmpxchg64() updates iter->old_spte
> > with
> > - * the current value, so the caller operates on fresh data, e.g. if
> > it
> > - * retries tdp_mmu_set_spte_atomic()
> > - */
> > - if (!try_cmpxchg64(sptep, &iter->old_spte, new_spte))
> > - return -EBUSY;
> > + if (is_mirror_sptep(iter->sptep) && !is_removed_spte(new_spte)) {
> > + int ret;
> > +
> > + /* Don't support atomic zapping for mirrored roots */
>
> The why is hidden in the commit message to patch 11. I wonder if it
> isn't clearer to simply squash together patches 10 and 11 (your call),
> and instead split out the addition of the new struct kvm parameters.
I actually split them in two for this v2. I thought the combined patch was too
big. Maybe I could just move this whole hunk to the next patch. I'll give it a
try.
>
> Anyway, this comment needs a bit more info:
>
> /*
> * Users of atomic zapping don't operate on mirror roots,
> * so only need to handle present new_spte.
> */
Ok.
>
> > + if (KVM_BUG_ON(!is_shadow_present_pte(new_spte), kvm))
> > + return -EBUSY;
> > + /*
> > + * Populating case.
> > + * - reflect_set_spte_present() implements
> > + * 1) Freeze SPTE
> > + * 2) call hooks to update mirrored page table,
> > + * 3) update SPTE to new_spte
> > + * - handle_changed_spte() only updates stats.
> > + */
>
> Comment not needed (weird I know).
Sure.
