1 files changed, 55 insertions, 0 deletions
diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
new file mode 100644
index 0000000..28fc4c5
--- /dev/null
+++ b/arch/riscv/include/asm/pgtable.h
@@ -0,0 +1,55 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/* Copyright (C) 2026 Richard Qin */
+
+#ifndef _ASM_RISCV_PGTABLE_H
+#define _ASM_RISCV_PGTABLE_H
+
+/*
+ * Early page-table construction API used by arch/riscv/mm/init.cc::setup_vm.
+ *
+ * Mirrors the create_pgd_mapping interface from Linux's
+ * arch/riscv/mm/init.c — same name, same semantics:
+ *
+ *   create_pgd_mapping(pgdir, va, pa, sz, prot)
+ *
+ *     pgdir : root of the page table to populate
+ *     va    : virtual address to map
+ *     pa    : physical address to map to
+ *     sz    : mapping size — must be a supported leaf size (PAGE_SIZE,
+ *             2 MiB megapage, or 1 GiB gigapage)
+ *     prot  : PTE flag bits (PAGE_KERNEL_EXEC etc., from <asm/page.h>)
+ *
+ * The boot-time variant in this file only supports gigapage (1 GiB)
+ * mappings — that is all setup_vm needs for the early_pg_dir / trampoline_pg_dir
+ * built before the slab allocator exists.  Finer-grained mappings come
+ * later via vmm_init().
+ */
+
+#include <lume/types.h>
+#include <asm/page.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+typedef struct { unsigned long pgd; } pgd_t;
+
+/* Linker-provided early page-table storage (defined in lumeos.lds.S
+ * ARCH_BSS_EXTRA, lives in .bss so it's zero-initialized).  Allocating
+ * them in the linker script — not in C — mirrors Linux and keeps the
+ * symbols visible from head.S without a forward C decl mismatch. */
+extern pgd_t early_pg_dir[PTRS_PER_PGD];
+extern pgd_t trampoline_pg_dir[PTRS_PER_PGD];
+extern pgd_t fixmap_pg_dir[PTRS_PER_PGD];
+
+/* Install a single PGD entry mapping `va` → `pa` with size `sz` and PTE
+ * flags `prot`.  Only sz == PGDIR_SIZE (1 GiB) is supported in this early
+ * variant — vmm_init() takes over with create_pgd_mapping_pmd later. */
+void create_pgd_mapping(pgd_t *pgdir, unsigned long va, unsigned long pa,
+                        unsigned long sz, unsigned long prot);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* _ASM_RISCV_PGTABLE_H */