On Wed, Jan 3, 2024 at 8:14 PM Liang Chen <liangchen.linux@xxxxxxxxx> wrote:
>
> On Wed, Jan 3, 2024 at 11:25 PM Sean Christopherson <seanjc@xxxxxxxxxx> wrote:
> >
> > +David
> >
> > On Wed, Jan 03, 2024, Liang Chen wrote:
> > > Count the number of zapped pages of tdp_mmu for vm stat.
> >
> > Why? I don't necessarily disagree with the change, but it's also not obvious
> > that this information is all that useful for the TDP MMU, e.g. the pf_fixed/taken
> > stats largely capture the same information.
> >
>
> We are attempting to make zapping specific to a particular memory
> slot, something like below.
>
> void kvm_tdp_zap_pages_in_memslot(struct kvm *kvm, struct kvm_memory_slot *slot)
> {
> struct kvm_mmu_page *root;
> bool shared = false;
> struct tdp_iter iter;
>
> gfn_t end = slot->base_gfn + slot->npages;
> gfn_t start = slot->base_gfn;
>
> write_lock(&kvm->mmu_lock);
> rcu_read_lock();
>
> for_each_tdp_mmu_root_yield_safe(kvm, root, false) {
>
> for_each_tdp_pte_min_level(iter, root,
> root->role.level, start, end) {
> if (tdp_mmu_iter_cond_resched(kvm, &iter, false, false))
> continue;
>
> if (!is_shadow_present_pte(iter.old_spte))
> continue;
>
> tdp_mmu_set_spte(kvm, &iter, 0);
> }
> }
>
> kvm_flush_remote_tlbs(kvm);
>
> rcu_read_unlock();
> write_unlock(&kvm->mmu_lock);
> }
>
> I noticed that it was previously done to the legacy MMU, but
> encountered some subtle issues with VFIO. I'm not sure if the issue is
> still there with TDP_MMU. So we are trying to do more tests and
> analyses before submitting a patch. This provides me a convenient way
> to observe the number of pages being zapped.
Note you could also use the existing tracepoint to observe the number
of pages being zapped in a given test run. e.g.
perf stat -e kvmmmu:kvm_mmu_prepare_zap_page -- <cmd>
