Re: [PATCH v2 4/6] KVM: x86/mmu: Track the number of TDP MMU pages, but not the actual pages

Yan Zhao
2022-07-27T03:02:30Z

On Sat, Jul 23, 2022 at 01:23:23AM +0000, Sean Christopherson wrote:

<snip>

> @@ -386,16 +385,18 @@ static void handle_changed_spte_dirty_log(struct kvm *kvm, int as_id, gfn_t gfn,
> static void tdp_mmu_unlink_sp(struct kvm *kvm, struct kvm_mmu_page *sp,
> bool shared)
> {
> + atomic64_dec(&kvm->arch.tdp_mmu_pages);
> +
> + if (!sp->nx_huge_page_disallowed)
> + return;
> +
Does this read of sp->nx_huge_page_disallowed also need to be protected by
tdp_mmu_pages_lock in shared path?

Thanks
Yan

> if (shared)
> spin_lock(&kvm->arch.tdp_mmu_pages_lock);
> else
> lockdep_assert_held_write(&kvm->mmu_lock);
>
> - list_del(&sp->link);
> - if (sp->nx_huge_page_disallowed) {
> - sp->nx_huge_page_disallowed = false;
> - untrack_possible_nx_huge_page(kvm, sp);
> - }
> + sp->nx_huge_page_disallowed = false;
> + untrack_possible_nx_huge_page(kvm, sp);
>
> if (shared)
> spin_unlock(&kvm->arch.tdp_mmu_pages_lock);
> @@ -1132,9 +1133,7 @@ static int tdp_mmu_link_sp(struct kvm *kvm, struct tdp_iter *iter,
> tdp_mmu_set_spte(kvm, iter, spte);
> }
>
> - spin_lock(&kvm->arch.tdp_mmu_pages_lock);
> - list_add(&sp->link, &kvm->arch.tdp_mmu_pages);
> - spin_unlock(&kvm->arch.tdp_mmu_pages_lock);
> + atomic64_inc(&kvm->arch.tdp_mmu_pages);
>
> return 0;
> }
> --
> 2.37.1.359.gd136c6c3e2-goog
>