v4.19.13 snapshot.
diff --git a/arch/x86/mm/ident_map.c b/arch/x86/mm/ident_map.c
new file mode 100644
index 0000000..fe7a125
--- /dev/null
+++ b/arch/x86/mm/ident_map.c
@@ -0,0 +1,139 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Helper routines for building identity mapping page tables. This is
+ * included by both the compressed kernel and the regular kernel.
+ */
+
+static void ident_pmd_init(struct x86_mapping_info *info, pmd_t *pmd_page,
+ unsigned long addr, unsigned long end)
+{
+ addr &= PMD_MASK;
+ for (; addr < end; addr += PMD_SIZE) {
+ pmd_t *pmd = pmd_page + pmd_index(addr);
+
+ if (pmd_present(*pmd))
+ continue;
+
+ set_pmd(pmd, __pmd((addr - info->offset) | info->page_flag));
+ }
+}
+
+static int ident_pud_init(struct x86_mapping_info *info, pud_t *pud_page,
+ unsigned long addr, unsigned long end)
+{
+ unsigned long next;
+
+ for (; addr < end; addr = next) {
+ pud_t *pud = pud_page + pud_index(addr);
+ pmd_t *pmd;
+
+ next = (addr & PUD_MASK) + PUD_SIZE;
+ if (next > end)
+ next = end;
+
+ if (info->direct_gbpages) {
+ pud_t pudval;
+
+ if (pud_present(*pud))
+ continue;
+
+ addr &= PUD_MASK;
+ pudval = __pud((addr - info->offset) | info->page_flag);
+ set_pud(pud, pudval);
+ continue;
+ }
+
+ if (pud_present(*pud)) {
+ pmd = pmd_offset(pud, 0);
+ ident_pmd_init(info, pmd, addr, next);
+ continue;
+ }
+ pmd = (pmd_t *)info->alloc_pgt_page(info->context);
+ if (!pmd)
+ return -ENOMEM;
+ ident_pmd_init(info, pmd, addr, next);
+ set_pud(pud, __pud(__pa(pmd) | info->kernpg_flag));
+ }
+
+ return 0;
+}
+
+static int ident_p4d_init(struct x86_mapping_info *info, p4d_t *p4d_page,
+ unsigned long addr, unsigned long end)
+{
+ unsigned long next;
+
+ for (; addr < end; addr = next) {
+ p4d_t *p4d = p4d_page + p4d_index(addr);
+ pud_t *pud;
+
+ next = (addr & P4D_MASK) + P4D_SIZE;
+ if (next > end)
+ next = end;
+
+ if (p4d_present(*p4d)) {
+ pud = pud_offset(p4d, 0);
+ ident_pud_init(info, pud, addr, next);
+ continue;
+ }
+ pud = (pud_t *)info->alloc_pgt_page(info->context);
+ if (!pud)
+ return -ENOMEM;
+ ident_pud_init(info, pud, addr, next);
+ set_p4d(p4d, __p4d(__pa(pud) | info->kernpg_flag));
+ }
+
+ return 0;
+}
+
+int kernel_ident_mapping_init(struct x86_mapping_info *info, pgd_t *pgd_page,
+ unsigned long pstart, unsigned long pend)
+{
+ unsigned long addr = pstart + info->offset;
+ unsigned long end = pend + info->offset;
+ unsigned long next;
+ int result;
+
+ /* Set the default pagetable flags if not supplied */
+ if (!info->kernpg_flag)
+ info->kernpg_flag = _KERNPG_TABLE;
+
+ /* Filter out unsupported __PAGE_KERNEL_* bits: */
+ info->kernpg_flag &= __default_kernel_pte_mask;
+
+ for (; addr < end; addr = next) {
+ pgd_t *pgd = pgd_page + pgd_index(addr);
+ p4d_t *p4d;
+
+ next = (addr & PGDIR_MASK) + PGDIR_SIZE;
+ if (next > end)
+ next = end;
+
+ if (pgd_present(*pgd)) {
+ p4d = p4d_offset(pgd, 0);
+ result = ident_p4d_init(info, p4d, addr, next);
+ if (result)
+ return result;
+ continue;
+ }
+
+ p4d = (p4d_t *)info->alloc_pgt_page(info->context);
+ if (!p4d)
+ return -ENOMEM;
+ result = ident_p4d_init(info, p4d, addr, next);
+ if (result)
+ return result;
+ if (pgtable_l5_enabled()) {
+ set_pgd(pgd, __pgd(__pa(p4d) | info->kernpg_flag));
+ } else {
+ /*
+ * With p4d folded, pgd is equal to p4d.
+ * The pgd entry has to point to the pud page table in this case.
+ */
+ pud_t *pud = pud_offset(p4d, 0);
+ set_pgd(pgd, __pgd(__pa(pud) | info->kernpg_flag));
+ }
+ }
+
+ return 0;
+}