KVM: X86: Add per-vm stat for max rmap list size

Add a new statistic max_mmu_rmap_size, which stores the maximum size of rmap
for the vm.
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20210625153214.43106-2-peterx@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/include/asm/kvm_host.h

@@ -1209,6 +1209,7 @@ struct kvm_vm_stat {
 	u64 lpages;
 	u64 nx_lpage_splits;
 	u64 max_mmu_page_hash_collisions;
+	u64 max_mmu_rmap_size;
 };
 
 struct kvm_vcpu_stat {

arch/x86/kvm/mmu/mmu.c

@@ -2698,6 +2698,8 @@ static int mmu_set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
 	if (is_shadow_present_pte(*sptep)) {
 		if (!was_rmapped) {
 			rmap_count = rmap_add(vcpu, sptep, gfn);
+			if (rmap_count > vcpu->kvm->stat.max_mmu_rmap_size)
+				vcpu->kvm->stat.max_mmu_rmap_size = rmap_count;
 			if (rmap_count > RMAP_RECYCLE_THRESHOLD)
 				rmap_recycle(vcpu, sptep, gfn);
 		}

arch/x86/kvm/x86.c

@@ -235,6 +235,7 @@ const struct _kvm_stats_desc kvm_vm_stats_desc[] = {
 	STATS_DESC_ICOUNTER(VM, mmu_unsync),
 	STATS_DESC_ICOUNTER(VM, lpages),
 	STATS_DESC_ICOUNTER(VM, nx_lpage_splits),
+	STATS_DESC_PCOUNTER(VM, max_mmu_rmap_size),
 	STATS_DESC_PCOUNTER(VM, max_mmu_page_hash_collisions)
 };
 static_assert(ARRAY_SIZE(kvm_vm_stats_desc) ==