Begin implementation of paging

5 files changed, 173 insertions, 5 deletions

diff --git a/kernel/Makefile b/kernel/Makefile
index 572bb3a..dec8686 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -3,7 +3,7 @@ AS = nasm
 ASFLAGS = -felf -g
 
 CC = i586-elf-gcc
-CFLAGS = -ffreestanding -O2 -std=gnu99 -Wall -Wextra -I . -I ./include -g
+CFLAGS = -ffreestanding -O2 -std=gnu99 -Wall -Wextra -I . -I ./include -g -Wno-unused-parameter
 # CXX = i586-elf-g++
 # CXFLAGS = -ffreestanding -O3 -Wall -Wextra -I . -I ./include -fno-exceptions -fno-rtti
 LD = i586-elf-gcc
@@ -12,7 +12,7 @@ LDFLAGS = -T linker.ld -ffreestanding -O2 -nostdlib -lgcc
 OBJ = lib/string.o lib/printf.o \
 	l0/loader.o l0/kmain.o l0/dbglog.o l0/sys.o \
 	l0/gdt.o l0/idt.o l0/interrupt.o \
-	l0/frame.o
+	l0/frame.o l0/paging.o
 OUT = kernel.bin
 
 all: $(OUT)
diff --git a/kernel/include/paging.h b/kernel/include/paging.h
new file mode 100644
index 0000000..5766e65
--- /dev/null
+++ b/kernel/include/paging.h
@@ -0,0 +1,25 @@
+#pragma once
+
+#include <sys.h>
+
+struct page_directory;
+typedef struct page_directory pagedir_t;
+
+
+void paging_setup(void* kernel_data_end);
+
+pagedir_t *get_current_pagedir();
+pagedir_t *get_kernel_pagedir();
+
+void switch_pagedir(pagedir_t *pd);
+
+uint32_t pd_get_frame(pagedir_t *pd, size_t vaddr);		// get physical frame for virtual address
+int pd_map_page(pagedir_t *pd,
+				size_t vaddr, uint32_t frame_id,
+				uint32_t rw);		// returns nonzero on error
+void pd_unmap_page(pagedir_t *pd, size_t vaddr);	// does nothing if page wasn't mapped
+
+pagedir_t *create_pagedir();		// returns zero on error
+void delete_pagedir(pagedir_t *pd);
+
+/* vim: set ts=4 sw=4 tw=0 noet :*/
diff --git a/kernel/l0/kmain.c b/kernel/l0/kmain.c
index b4e2ef1..f6cda4e 100644
--- a/kernel/l0/kmain.c
+++ b/kernel/l0/kmain.c
@@ -6,6 +6,7 @@
 #include <gdt.h>
 #include <idt.h>
 #include <frame.h>
+#include <paging.h>
 
 void breakpoint_handler(registers_t *regs) {
 	dbg_printf("Breakpoint! (int3)\n");
@@ -34,10 +35,14 @@ void kmain(struct multiboot_info_t *mbd, int32_t mb_magic) {
 	// a pointer to this pointer is passed to the functions that might have
 	// to allocate memory ; they just increment it of the allocated quantity
 	void* kernel_data_end = (void*)K_END_ADDR;
+
 	frame_init_allocator(total_ram, &kernel_data_end);
 	dbg_printf("kernel_data_end: 0x%p\n", kernel_data_end);
 	dbg_print_frame_stats();
 
+	paging_setup(kernel_data_end);
+	dbg_printf("Paging seems to be working!\n");
+
 	// TODO:
 	// - setup allocator for physical pages (eg: buddy allocator, see OSDev wiki)
 	// - setup allocator for virtual memory space
diff --git a/kernel/l0/loader.s b/kernel/l0/loader.s
index 0f57549..e4c4611 100644
--- a/kernel/l0/loader.s
+++ b/kernel/l0/loader.s
@@ -1,5 +1,6 @@
 [EXTERN kmain]            ; kmain is defined in kmain.c
 [GLOBAL loader]           ; making entry point visible to linker
+[GLOBAL kernel_pagedir]   ; make kernel page directory visible
 
 ; higher-half kernel setup
 K_HIGHHALF_ADDR     equ 0xC0000000
@@ -24,7 +25,8 @@ multiboot_header:
 
 loader:	
 	; setup the boot page directory used for higher-half
-	mov ecx, boot_pagedir
+	mov ecx, kernel_pagedir
+	sub ecx, K_HIGHHALF_ADDR	; access its lower-half address
 	mov cr3, ecx
 
 	; Set PSE bit in CR4 to enable 4MB pages.
@@ -41,8 +43,9 @@ loader:
 	lea ecx, [higherhalf]
 	jmp ecx
 
+[section .data]
 align 0x1000
-boot_pagedir:
+kernel_pagedir:
 	; uses 4MB pages
 	; identity-maps the first 4Mb of RAM, and also maps them with offset += k_highhalf_addr
 	dd 0x00000083
@@ -53,7 +56,7 @@ boot_pagedir:
 [section .text]
 higherhalf:		; now we're running in higher half
 	; unmap first 4Mb
-	mov dword [boot_pagedir], 0
+	mov dword [kernel_pagedir], 0
 	invlpg [0]
 
 	mov esp, stack_top          ; set up the stack
diff --git a/kernel/l0/paging.c b/kernel/l0/paging.c
new file mode 100644
index 0000000..9e9df6b
--- /dev/null
+++ b/kernel/l0/paging.c
@@ -0,0 +1,135 @@
+#include <paging.h>
+#include <frame.h>
+
+typedef union page {
+	struct {
+		uint32_t present		: 1;
+		uint32_t rw				: 1;
+		uint32_t user			: 1;
+		uint32_t write_through  : 1;
+		uint32_t disable_cache	: 1;
+		uint32_t accessed		: 1;
+		uint32_t dirty			: 1;	// only PTE
+		uint32_t size_4m		: 1;	// only PDE
+		uint32_t global			: 1;	// only PTE
+		uint32_t rsvd			: 3;
+		uint32_t frame			: 20;
+	};
+	uint32_t as_int32;
+} page_t;
+
+typedef struct page_table {
+	page_t page[1024];
+} pagetable_t;
+
+struct page_directory {
+	pagetable_t *pt[1024];	// virtual addresses of each page table
+	pagetable_t *dir;		// virtual address of page directory
+	size_t phys_addr;		// physical address of page directory
+};
+
+
+// access kernel page directory page defined in loader.s
+// (this is a correct higher-half address)
+extern pagetable_t kernel_pagedir;
+
+static pagetable_t __attribute__((aligned(PAGE_SIZE))) kernel_pt768;
+static pagedir_t kernel_pd;
+
+static pagedir_t *current_pd;
+
+void paging_setup(void* kernel_data_end) {
+	size_t n_kernel_pages =
+		PAGE_ALIGN_UP((size_t)kernel_data_end - K_HIGHHALF_ADDR)/PAGE_SIZE;
+
+	ASSERT(n_kernel_pages <= 1024);
+
+	// setup kernel_pd structure
+	kernel_pd.dir = &kernel_pagedir;
+	kernel_pd.phys_addr = (size_t)kernel_pd.dir - K_HIGHHALF_ADDR;
+	for (size_t i = 0; i < 1024; i++) kernel_pd.pt[i] = 0;
+
+	// setup kernel_pt768
+	for (size_t i = 0; i < n_kernel_pages; i++) {
+		kernel_pt768.page[i].as_int32 = 0;	// clear any junk
+		kernel_pt768.page[i].present = 1;
+		kernel_pt768.page[i].user = 0;
+		kernel_pt768.page[i].rw = 1;
+		kernel_pt768.page[i].frame = i;
+	}
+	for (size_t i = n_kernel_pages; i < 1024; i++){
+		kernel_pt768.page[i].as_int32 = 0;
+	}
+
+	// replace 4M mapping by kernel_pt768
+	kernel_pd.pt[768] = &kernel_pt768;
+	kernel_pd.dir->page[768].as_int32 =
+		(((size_t)&kernel_pt768 - K_HIGHHALF_ADDR) & PAGE_MASK) | 0x07;
+
+	current_pd = &kernel_pd;
+
+	// paging already enabled in loader, nothing to do.
+
+	// disable 4M pages (remove PSE bit in CR4)
+	uint32_t cr4;
+	asm volatile("movl %%cr4, %0": "=r"(cr4));
+	cr4 &= ~0x00000010;
+	asm volatile("movl %0, %%cr4":: "r"(cr4));
+
+	// TODO : setup page fault handler
+}
+
+pagedir_t *get_current_pagedir() {
+	return current_pd;
+}
+
+pagedir_t *get_kernel_pagedir() {
+	return &kernel_pd;
+}
+
+void switch_pagedir(pagedir_t *pd) {
+    asm volatile("movl %0, %%cr3":: "r"(pd->phys_addr));
+}
+
+// ============================== //
+// Mapping and unmapping of pages //
+// ============================== //
+
+uint32_t pd_get_frame(pagedir_t *pd, size_t vaddr) {
+	uint32_t page = vaddr / PAGE_SIZE;
+	uint32_t pt = page / PAGE_SIZE;
+	uint32_t pt_page = page % PAGE_SIZE;
+
+	if (pd == 0) return 0;
+	if (pd->pt[pt] == 0) return 0;
+	if (!pd->pt[pt]->page[pt_page].present) return 0;
+	return pd->pt[pt]->page[pt_page].frame;
+}
+
+int pd_map_page(pagedir_t *pd, size_t vaddr, uint32_t frame_id, uint32_t rw) {
+	return 1; 	// TODO
+} 
+
+void pd_unmap_page(pagedir_t *pd, size_t vaddr) {
+	uint32_t page = vaddr / PAGE_SIZE;
+	uint32_t pt = page / PAGE_SIZE;
+	uint32_t pt_page = page % PAGE_SIZE;
+
+	if (pd == 0) return;
+	if (pd->pt[pt] == 0) return;
+	if (!pd->pt[pt]->page[pt_page].present) return;
+	pd->pt[pt]->page[pt_page].as_int32 = 0;
+
+	// TODO (?) : if pagetable is completely empty, free it
+}
+
+// Creation and deletion of page directories
+
+pagedir_t *create_pagedir() {
+	return 0;	// TODO
+}
+void delete_pagedir(pagedir_t *pd) {
+	return;		// TODO
+}
+
+/* vim: set ts=4 sw=4 tw=0 noet :*/