lkm: add is2mb, no usage yet

code/lkm.c

@@ -1,9 +1,11 @@
+#include <asm/pgtable_64.h>
 #include <linux/device.h>
 #include <linux/fs.h>
 #include <linux/init.h>
 #include <linux/module.h>
 #include <linux/proc_fs.h>
 #include <linux/uaccess.h>
+#include <stddef.h>
 
 #define DEVICE_NAME "lkm"
 #define CLASS_NAME  "lkmclass"
@@ -25,6 +27,48 @@ static struct file_operations lkm_fops = {
 	.unlocked_ioctl = lkm_ioctl,
 };
 
+void
+is2mb(size_t addr)
+{
+	unsigned long above = ((long)addr) >> __VIRTUAL_MASK_SHIFT;
+	pgd_t *pgd;
+	p4d_t *p4d;
+	pud_t *pud;
+	pmd_t *pmd;
+	pte_t *pte;
+
+	if (above != 0 && above != -1UL)
+		return 0;
+
+	pgd = pgd_offset_pgd(_init_top_pgt, addr);
+	if (pgd_none(*pgd))
+		return 0;
+
+	p4d = p4d_offset(pgd, addr);
+	if (!p4d_present(*p4d))
+		return 0;
+
+	pud = pud_offset(p4d, addr);
+	if (!pud_present(*pud))
+		return 0;
+
+	if (pud_large(*pud))
+		return 0;
+
+	pmd = pmd_offset(pud, addr);
+	if (!pmd_present(*pmd))
+		return 0;
+
+	if (pmd_large(*pmd))
+		return 1;
+
+	pte = pte_offset_kernel(pmd, addr);
+	if (pte_none(*pte))
+		return 0;
+
+	return 0;
+}
+
 static int
 lkm_init(void)
 {