KVM: arm64/mmu: count KVM s2 mmu usage in secondary pagetable stats

Count the pages used by KVM in arm64 for stage2 mmu in memory stats
under secondary pagetable stats (e.g. "SecPageTables" in /proc/meminfo)
to give better visibility into the memory consumption of KVM mmu in a
similar way to how normal user page tables are accounted.
Signed-off-by: Yosry Ahmed <yosryahmed@google.com>
Reviewed-by: Oliver Upton <oliver.upton@linux.dev>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220823004639.2387269-5-yosryahmed@google.comSigned-off-by: Sean Christopherson <seanjc@google.com>

arch/arm64/kvm/mmu.c

@@ -92,9 +92,13 @@ static bool kvm_is_device_pfn(unsigned long pfn)
 static void *stage2_memcache_zalloc_page(void *arg)
 {
 	struct kvm_mmu_memory_cache *mc = arg;
+	void *virt;
 
 	/* Allocated with __GFP_ZERO, so no need to zero */
-	return kvm_mmu_memory_cache_alloc(mc);
+	virt = kvm_mmu_memory_cache_alloc(mc);
+	if (virt)
+		kvm_account_pgtable_pages(virt, 1);
+	return virt;
 }
 
 static void *kvm_host_zalloc_pages_exact(size_t size)
@@ -102,6 +106,21 @@ static void *kvm_host_zalloc_pages_exact(size_t size)
 	return alloc_pages_exact(size, GFP_KERNEL_ACCOUNT | __GFP_ZERO);
 }
 
+static void *kvm_s2_zalloc_pages_exact(size_t size)
+{
+	void *virt = kvm_host_zalloc_pages_exact(size);
+
+	if (virt)
+		kvm_account_pgtable_pages(virt, (size >> PAGE_SHIFT));
+	return virt;
+}
+
+static void kvm_s2_free_pages_exact(void *virt, size_t size)
+{
+	kvm_account_pgtable_pages(virt, -(size >> PAGE_SHIFT));
+	free_pages_exact(virt, size);
+}
+
 static void kvm_host_get_page(void *addr)
 {
 	get_page(virt_to_page(addr));
@@ -112,6 +131,15 @@ static void kvm_host_put_page(void *addr)
 	put_page(virt_to_page(addr));
 }
 
+static void kvm_s2_put_page(void *addr)
+{
+	struct page *p = virt_to_page(addr);
+	/* Dropping last refcount, the page will be freed */
+	if (page_count(p) == 1)
+		kvm_account_pgtable_pages(addr, -1);
+	put_page(p);
+}
+
 static int kvm_host_page_count(void *addr)
 {
 	return page_count(virt_to_page(addr));
@@ -625,10 +653,10 @@ static int get_user_mapping_size(struct kvm *kvm, u64 addr)
 
 static struct kvm_pgtable_mm_ops kvm_s2_mm_ops = {
 	.zalloc_page		= stage2_memcache_zalloc_page,
-	.zalloc_pages_exact	= kvm_host_zalloc_pages_exact,
-	.free_pages_exact	= free_pages_exact,
+	.zalloc_pages_exact	= kvm_s2_zalloc_pages_exact,
+	.free_pages_exact	= kvm_s2_free_pages_exact,
 	.get_page		= kvm_host_get_page,
-	.put_page		= kvm_host_put_page,
+	.put_page		= kvm_s2_put_page,
 	.page_count		= kvm_host_page_count,
 	.phys_to_virt		= kvm_host_va,
 	.virt_to_phys		= kvm_host_pa,