KVM: x86/mmu: add missing update to max_mmu_rmap_size

The update to statistic max_mmu_rmap_size is unintentionally removed by
commit 4293ddb7 ("KVM: x86/mmu: Remove redundant spte present check
in mmu_set_spte"). Add missing update to it or max_mmu_rmap_size will
always be nonsensical 0.

Fixes: 4293ddb7 ("KVM: x86/mmu: Remove redundant spte present check in mmu_set_spte")
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Message-Id: <20220907080657.42898-1-linmiaohe@huawei.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/mmu/mmu.c

@@ -1596,6 +1596,8 @@ static void __rmap_add(struct kvm *kvm,
 	rmap_head = gfn_to_rmap(gfn, sp->role.level, slot);
 	rmap_count = pte_list_add(cache, spte, rmap_head);
 
+	if (rmap_count > kvm->stat.max_mmu_rmap_size)
+		kvm->stat.max_mmu_rmap_size = rmap_count;
 	if (rmap_count > RMAP_RECYCLE_THRESHOLD) {
 		kvm_zap_all_rmap_sptes(kvm, rmap_head);
 		kvm_flush_remote_tlbs_with_address(