KVM: x86/mmu: Commit zap of remaining invalid pages when recovering lpages

Call kvm_mmu_commit_zap_page() after exiting the "prepare zap" loop in
kvm_recover_nx_lpages() to finish zapping pages in the unlikely event
that the loop exited due to lpage_disallowed_mmu_pages being empty.
Because the recovery thread drops mmu_lock() when rescheduling, it's
possible that lpage_disallowed_mmu_pages could be emptied by a different
thread without to_zap reaching zero despite to_zap being derived from
the number of disallowed lpages.

Fixes: 1aa9b957 ("kvm: x86: mmu: Recovery of shattered NX large pages")
Cc: Junaid Shahid <junaids@google.com>
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Message-Id: <20200923183735.584-2-sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/mmu/mmu.c

@@ -6394,6 +6394,7 @@ static void kvm_recover_nx_lpages(struct kvm *kvm)
 				cond_resched_lock(&kvm->mmu_lock);
 		}
 	}
+	kvm_mmu_commit_zap_page(kvm, &invalid_list);
 
 	spin_unlock(&kvm->mmu_lock);
 	srcu_read_unlock(&kvm->srcu, rcu_idx);