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-rw-r--r--na/arch/riscv/mm/init.cc241
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diff --git a/na/arch/riscv/mm/init.cc b/na/arch/riscv/mm/init.cc
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-/* SPDX-License-Identifier: GPL-2.0-or-later */
-/* Copyright (C) 2026 Richard Qin */
-
-/*
- * RISC-V early memory-management bootstrap.
- *
- * Mirrors Linux arch/riscv/mm/init.c — same file name, same C function
- * names (setup_vm / relocate_enable_mmu / relocate_kernel), same global
- * state (kernel_map, early_pg_dir, trampoline_pg_dir). head.S calls
- * setup_vm immediately after BSS-clear, then later calls
- * relocate_enable_mmu, which switches SATP, jumps to higher-half VA,
- * and finally calls relocate_kernel to apply .rela.dyn.
- *
- * Differences from Linux:
- * - KASLR offset is hard-wired to 0 for now (no pi/ subsystem) — the
- * code path that would consume kernel_map.virt_offset is in place
- * so adding pi/-based seed reading later only requires populating
- * that one field.
- * - Only 1 GiB superpages supported in create_pgd_mapping; sufficient
- * for the early page tables. Finer-grained mappings come from
- * vmm_init() once slab is up.
- */
-
-#include <lume/init.h>
-#include <lume/setup.h>
-#include <lume/elf.h>
-#include <lume/kernel_map.h>
-#include <lume/types.h>
-#include <asm/page.h>
-#include <asm/csr.h>
-#include <asm/pgtable.h>
-#include <asm/sections.h>
-
-/*
- * Global kernel mapping descriptor — single source of truth for the
- * runtime-vs-link address relationship. Lives in .data so its initial
- * zero contents survive the BSS-clear that runs before setup_vm fills
- * the fields. Read by VMM, page-fault handler, ptdump, etc.
- *
- * Linux equivalent: arch/riscv/mm/init.c::kernel_map
- */
-struct kernel_mapping kernel_map __attribute__((section(".data")));
-
-/*
- * create_pgd_mapping — install one PGD entry covering a 1 GiB region.
- *
- * Only 1 GiB superpages are supported in this early variant; setup_vm
- * needs nothing finer. Identical interface to Linux's same-named
- * function in arch/riscv/mm/init.c, restricted in arity.
- */
-extern "C" void create_pgd_mapping(pgd_t *pgdir, unsigned long va,
- unsigned long pa, unsigned long sz,
- unsigned long prot)
-{
- /* This early variant only supports 1 GiB superpages. */
- if (sz != PGDIR_SIZE) {
- return;
- }
-
- /* SV39 PGD index = (va >> 30) & 0x1FF — see Volume II, §4.4.1.
- * Each PGD entry is 8 bytes; pgdir[i] is the slot for that VPN[2]. */
- unsigned long idx = (va >> PGDIR_SHIFT) & (PTRS_PER_PGD - 1);
-
- /* PTE PPN field: physical page number shifted up by 10 (SV39 PTE
- * layout: bits [53:10] = PPN, bits [9:0] = flags). */
- unsigned long ppn = pa >> PAGE_SHIFT;
- pgdir[idx].pgd = (ppn << 10) | prot;
-}
-
-/*
- * setup_vm — fill kernel_map and build early_pg_dir + trampoline_pg_dir.
- *
- * Called from head.S after BSS is cleared, with:
- * load_pa = runtime physical address of _start
- * dtb_pa = physical address of the device tree blob (from a1)
- *
- * Mirrors Linux arch/riscv/mm/init.c::setup_vm. The actual SATP write
- * happens later in relocate_enable_mmu; here we only populate page
- * tables and the kernel_map descriptor.
- */
-extern "C" void __init setup_vm(uintptr_t load_pa, uintptr_t dtb_pa)
-{
- (void)dtb_pa; /* KASLR pi/ subsystem will consume this later. */
-
- /* --- 1. Fill kernel_map ----------------------------------------- */
-
- /* KASLR offset = 0 in this configuration. */
- kernel_map.virt_offset = 0;
- kernel_map.virt_addr = KERNEL_LINK_ADDR + kernel_map.virt_offset;
- kernel_map.phys_addr = load_pa;
- kernel_map.size = (uintptr_t)_end - (uintptr_t)_start;
- kernel_map.page_offset = PAGE_OFFSET;
-
- /* Mirrors Linux: va_pa_offset is the constant added to a physical
- * address to obtain its direct-map VA. */
- kernel_map.va_pa_offset = PAGE_OFFSET - load_pa;
-
- /* va_kernel_pa_offset is the constant added to a load PA to obtain
- * the kernel's link VA (used by relocate_enable_mmu to fix sp/ra). */
- kernel_map.va_kernel_pa_offset = kernel_map.virt_addr - load_pa;
-
- /* --- 2. Build early_pg_dir ------------------------------------- *
- *
- * SV39 root page table — 4 entries cover identity + higher-half for
- * both MMIO (PA 0x0000_0000, 1 GiB) and RAM (PA 0x8000_0000, 1 GiB):
- *
- * [0] identity PA 0x0000_0000 → VA 0x0000_0000
- * [2] identity PA 0x8000_0000 → VA 0x8000_0000
- * [256] high-half PA 0x0000_0000 → VA 0xFFFFFFC000000000
- * [258] high-half PA 0x8000_0000 → VA 0xFFFFFFC080000000
- *
- * Identity mappings keep PC valid right after csrw satp. High-half
- * mappings let the post-MMU `jr` to .Lhigher_half resolve. */
- create_pgd_mapping(early_pg_dir, 0x00000000UL, 0x00000000UL,
- PGDIR_SIZE, PAGE_KERNEL_EXEC);
- create_pgd_mapping(early_pg_dir, 0x80000000UL, 0x80000000UL,
- PGDIR_SIZE, PAGE_KERNEL_EXEC);
- create_pgd_mapping(early_pg_dir, PAGE_OFFSET + 0x00000000UL,
- 0x00000000UL, PGDIR_SIZE, PAGE_KERNEL_EXEC);
- create_pgd_mapping(early_pg_dir, PAGE_OFFSET + 0x80000000UL,
- 0x80000000UL, PGDIR_SIZE, PAGE_KERNEL_EXEC);
-
- /* --- 3. Build trampoline_pg_dir -------------------------------- *
- *
- * The trampoline maps just the gigapage containing _start, both at
- * its identity PA and at its higher-half VA. This is the page
- * table SATP holds during the single instruction window between
- * "MMU off" and "MMU on with early_pg_dir" — the PC must resolve
- * under both, so we re-use the same two entries above. */
- create_pgd_mapping(trampoline_pg_dir, load_pa & PGDIR_MASK,
- load_pa & PGDIR_MASK, PGDIR_SIZE, PAGE_KERNEL_EXEC);
- create_pgd_mapping(trampoline_pg_dir,
- (kernel_map.virt_addr) & PGDIR_MASK,
- load_pa & PGDIR_MASK, PGDIR_SIZE, PAGE_KERNEL_EXEC);
-}
-
-/*
- * relocate_kernel — walk .rela.dyn and apply R_RISCV_RELATIVE entries.
- *
- * Called from relocate_enable_mmu *after* the SATP switch and the jump
- * to higher-half VA — meaning __rela_dyn_start / __rela_dyn_end resolve
- * to valid higher-half pointers we can dereference directly.
- *
- * Mirrors Linux arch/riscv/mm/init.c::relocate_kernel. Key invariant:
- * even when kaslr_offset == 0, the slot store MUST still happen — the
- * linker leaves R_RISCV_RELATIVE slots zero-filled at link time, and
- * only relocate_kernel writes the link-time addend into them. Without
- * this pass, .init_array entries (and every other relocated symbol)
- * are NULL pointers.
- */
-void __init relocate_kernel(void)
-{
- auto *rela = (Elf64_Rela *)__rela_dyn_start;
- auto *rela_end = (Elf64_Rela *)__rela_dyn_end;
-
- const uint64 kaslr_offset = kernel_map.virt_offset;
-
- for (; rela < rela_end; ++rela) {
- if (ELF64_R_TYPE(rela->r_info) != R_RISCV_RELATIVE) {
- continue;
- }
- auto *slot = (Elf64_Addr *)(rela->r_offset + kaslr_offset);
- *slot = (Elf64_Addr)(rela->r_addend) + kaslr_offset;
- }
-}
-
-/*
- * relocate_enable_mmu — switch SATP, jump to higher-half, apply relocations.
- *
- * Called from head.S after setup_vm has filled kernel_map and built the
- * page tables. Equivalent to Linux's same-named asmlinkage routine but
- * written in C++ so it can share kernel_map / pgtable definitions with
- * setup_vm directly.
- *
- * Three logical steps:
- *
- * 1. csrw satp ← trampoline_pg_dir. PC continues running at the
- * identity PA, which the trampoline still maps; the high-half PA
- * mapping is now also live.
- *
- * 2. la t0, .Lvirt; add t0, t0, va_kernel_pa_offset; jr t0.
- * A PC-relative `la` under medany yields the runtime PA of the
- * label; adding va_kernel_pa_offset (= link_va - load_pa) converts
- * it to the link-time higher-half VA, which the trampoline maps.
- * The `jr` then atomically pushes PC into higher-half space.
- *
- * 3. csrw satp ← early_pg_dir. We're now executing at higher-half
- * VA, so the trampoline can be retired in favour of the full
- * early page table. sp / ra / gp must be slid to higher-half too,
- * otherwise the next ret-or-call uses physical-low addresses
- * whose mapping is about to disappear when vmm_init drops the
- * identity entries.
- *
- * 4. Call relocate_kernel — now safe, because all link-time VA
- * pointers in __rela_dyn_start[..] dereference correctly.
- */
-extern "C" void __init relocate_enable_mmu(pgd_t *pgdir)
-{
- (void)pgdir; /* head.S passes early_pg_dir for documentation; we
- * read the global symbol directly inside the asm. */
-
- const unsigned long va_kernel_pa_offset = kernel_map.va_kernel_pa_offset;
- const unsigned long satp_mode = SATP_MODE_SV39;
-
- asm volatile (
- /* Step 1: csrw satp <- trampoline */
- "la t0, trampoline_pg_dir\n"
- "srli t0, t0, 12\n"
- "or t0, t0, %[mode]\n"
- "csrw satp, t0\n"
- "sfence.vma\n"
-
- /* Step 2: jump to higher-half VA */
- "la t0, 1f\n"
- "add t0, t0, %[off]\n"
- "jr t0\n"
- "1:\n"
-
- /* Step 3a: csrw satp <- early_pg_dir (now in higher-half) */
- "la t0, early_pg_dir\n"
- "srli t0, t0, 12\n"
- "or t0, t0, %[mode]\n"
- "csrw satp, t0\n"
- "sfence.vma\n"
-
- /* Step 3b: slide sp / ra / gp to higher-half */
- "add sp, sp, %[off]\n"
- "add ra, ra, %[off]\n"
- ".option push\n"
- ".option norelax\n"
- "la gp, __global_pointer$\n"
- ".option pop\n"
- :
- : [off] "r"(va_kernel_pa_offset),
- [mode] "r"(satp_mode)
- : "t0", "memory"
- );
-
- /* Step 4: apply .rela.dyn now that VA dereferences work. */
- relocate_kernel();
-}
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