Begin implementation of paging

1 files changed, 135 insertions, 0 deletions

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 :*/