KVM: arm64: Count pKVM stage-2 usage in secondary pagetable stats

Count the pages used by pKVM for the guest stage-2 in memory stats under
secondary pagetable, similarly to what the VHE mode does.

Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
Acked-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20250313114038.1502357-4-vdonnefort@google.com
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>

arch/arm64/include/asm/kvm_host.h

@@ -86,6 +86,8 @@ struct kvm_hyp_memcache {
 	phys_addr_t head;
 	unsigned long nr_pages;
 	struct pkvm_mapping *mapping; /* only used from EL1 */
+
+#define	HYP_MEMCACHE_ACCOUNT_STAGE2	BIT(1)
 	unsigned long flags;
 };
 

arch/arm64/kvm/mmu.c

@@ -1088,12 +1088,24 @@ void kvm_free_stage2_pgd(struct kvm_s2_mmu *mmu)
 
 static void hyp_mc_free_fn(void *addr, void *mc)
 {
+	struct kvm_hyp_memcache *memcache = mc;
+
+	if (memcache->flags & HYP_MEMCACHE_ACCOUNT_STAGE2)
+		kvm_account_pgtable_pages(addr, -1);
+
 	free_page((unsigned long)addr);
 }
 
 static void *hyp_mc_alloc_fn(void *mc)
 {
-	return (void *)__get_free_page(GFP_KERNEL_ACCOUNT);
+	struct kvm_hyp_memcache *memcache = mc;
+	void *addr;
+
+	addr = (void *)__get_free_page(GFP_KERNEL_ACCOUNT);
+	if (addr && memcache->flags & HYP_MEMCACHE_ACCOUNT_STAGE2)
+		kvm_account_pgtable_pages(addr, 1);
+
+	return addr;
 }
 
 void free_hyp_memcache(struct kvm_hyp_memcache *mc)

arch/arm64/kvm/pkvm.c

@@ -165,12 +165,16 @@ static int __pkvm_create_hyp_vm(struct kvm *host_kvm)
 	handle = ret;
 
 	host_kvm->arch.pkvm.handle = handle;
+	host_kvm->arch.pkvm.stage2_teardown_mc.flags |= HYP_MEMCACHE_ACCOUNT_STAGE2;
+	kvm_account_pgtable_pages(pgd, pgd_sz / PAGE_SIZE);
 
 	/* Donate memory for the vcpus at hyp and initialize it. */
 	hyp_vcpu_sz = PAGE_ALIGN(PKVM_HYP_VCPU_SIZE);
 	kvm_for_each_vcpu(idx, host_vcpu, host_kvm) {
 		void *hyp_vcpu;
 
+		host_vcpu->arch.pkvm_memcache.flags |= HYP_MEMCACHE_ACCOUNT_STAGE2;
+
 		/* Indexing of the vcpus to be sequential starting at 0. */
 		if (WARN_ON(host_vcpu->vcpu_idx != idx)) {
 			ret = -EINVAL;