1 files changed, 298 insertions, 0 deletions
diff --git a/src/kernel/core/paging.c b/src/kernel/core/paging.c
new file mode 100644
index 0000000..e60ca53
--- /dev/null
+++ b/src/kernel/core/paging.c
@@ -0,0 +1,298 @@
+#include <paging.h>
+#include <frame.h>
+#include <idt.h>
+#include <dbglog.h>
+#include <region.h>
+#include <mutex.h>
+#include <thread.h>
+#include <malloc.h>
+
+#define PAGE_OF_ADDR(x)		(((size_t)x >> PAGE_SHIFT) % N_PAGES_IN_PT)
+#define PT_OF_ADDR(x)		((size_t)x >> (PAGE_SHIFT + PT_SHIFT))
+
+#define PTE_PRESENT			(1<<0)
+#define PTE_RW				(1<<1)
+#define PTE_USER			(1<<2)
+#define PTE_WRITE_THROUGH	(1<<3)
+#define PTE_DISABLE_CACHE	(1<<4)
+#define PTE_ACCESSED		(1<<5)
+#define PTE_DIRTY			(1<<6)		// only PTE
+#define PTE_SIZE_4M			(1<<7)		// only PDE
+#define PTE_GLOBAL			(1<<8)		// only PTE
+#define PTE_FRAME_SHIFT		12
+
+typedef struct page_table {
+	uint32_t page[1024];
+} pagetable_t;
+
+struct page_directory {
+	uint32_t phys_addr;		// physical address of page directory
+	// to modify a page directory, we first map it
+	// then we can use mirroring to edit it
+	// (the last 4M of the address space are mapped to the PD itself)
+
+	mutex_t mutex;
+};
+
+
+// access kernel page directory page defined in loader.s
+// (this is a correct higher-half address)
+extern pagetable_t kernel_pd;
+
+// pre-allocate a page table so that we can map the first 4M of kernel memory
+static pagetable_t __attribute__((aligned(PAGE_SIZE))) kernel_pt0;
+
+extern char kernel_stack_protector;
+
+static pagedir_t kernel_pd_d;
+
+#define current_pt ((pagetable_t*)PD_MIRROR_ADDR)
+#define current_pd ((pagetable_t*)(PD_MIRROR_ADDR + (N_PAGES_IN_PT-1)*PAGE_SIZE))
+
+void page_fault_handler(registers_t *regs) {
+	void* vaddr;
+	asm volatile("movl %%cr2, %0":"=r"(vaddr));
+
+	if ((size_t)vaddr >= K_HIGHHALF_ADDR) {
+		uint32_t pt = PT_OF_ADDR(vaddr);
+
+		if (current_pd != &kernel_pd && current_pd->page[pt] != kernel_pd.page[pt]) {
+			current_pd->page[pt] = kernel_pd.page[pt];
+			invlpg(&current_pt[pt]);
+			return;
+		}
+		if (regs->eflags & EFLAGS_IF) asm volatile("sti");	// from now on we are preemptible
+
+		if (vaddr >= (void*)&kernel_stack_protector && vaddr < (void*)&kernel_stack_protector + PAGE_SIZE) {
+			dbg_printf("Kernel stack overflow at 0x%p\n", vaddr);
+			PANIC("Kernel stack overflow.");
+		}
+
+		if ((size_t)vaddr >= PD_MIRROR_ADDR) {
+			dbg_printf("Fault on access to mirrorred PD at 0x%p\n", vaddr);
+			dbg_print_region_info();
+			PANIC("Unhandled kernel space page fault");
+		}
+
+		region_info_t *i = find_region(vaddr);
+		if (i == 0) {
+			dbg_printf("Kernel pagefault in non-existing region at 0x%p\n", vaddr);
+			dbg_dump_registers(regs);
+			PANIC("Unhandled kernel space page fault");
+		}
+		if (i->pf == 0) {
+			dbg_printf("Kernel pagefault in region with no handler at 0x%p\n", vaddr);
+			dbg_dump_registers(regs);
+			dbg_print_region_info();
+			PANIC("Unhandled kernel space page fault");
+		}
+		i->pf(get_current_pagedir(), i, vaddr);
+	} else {
+		if (regs->eflags & EFLAGS_IF) asm volatile("sti");	// userspace PF handlers should always be preemptible
+
+		dbg_printf("Userspace page fault at 0x%p\n", vaddr);
+		PANIC("Unhandled userspace page fault");
+		// not handled yet
+		// TODO
+	}
+}
+
+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);	// we use less than 4M for kernel
+
+	// setup kernel_pd_d structure
+	kernel_pd_d.phys_addr = (size_t)&kernel_pd - K_HIGHHALF_ADDR;
+	kernel_pd_d.mutex = MUTEX_UNLOCKED;
+
+	// setup kernel_pt0
+	ASSERT(PAGE_OF_ADDR(K_HIGHHALF_ADDR) == 0);	// kernel is 4M-aligned
+	ASSERT(FIRST_KERNEL_PT == 768);
+	for (size_t i = 0; i < n_kernel_pages; i++) {
+		if ((i * PAGE_SIZE) + K_HIGHHALF_ADDR == (size_t)&kernel_stack_protector) {
+			kernel_pt0.page[i] = 0;	// don't map kernel stack protector page
+			frame_free(i, 1);
+		} else {
+			kernel_pt0.page[i] = (i << PTE_FRAME_SHIFT) | PTE_PRESENT | PTE_RW | PTE_GLOBAL;
+		}
+	}
+	for (size_t i = n_kernel_pages; i < 1024; i++){
+		kernel_pt0.page[i] = 0;
+	}
+
+	// replace 4M mapping by kernel_pt0
+	kernel_pd.page[FIRST_KERNEL_PT] =
+		(((size_t)&kernel_pt0 - K_HIGHHALF_ADDR) & PAGE_MASK) | PTE_PRESENT | PTE_RW;
+	// set up mirroring
+	kernel_pd.page[N_PAGES_IN_PT-1] =
+		(((size_t)&kernel_pd - K_HIGHHALF_ADDR) & PAGE_MASK) | PTE_PRESENT | PTE_RW;
+
+	invlpg((void*)K_HIGHHALF_ADDR);
+
+	// 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));
+
+	idt_set_ex_handler(EX_PAGE_FAULT, page_fault_handler);
+}
+
+pagedir_t *get_current_pagedir() {
+	if (current_thread == 0) return &kernel_pd_d;
+	return current_thread->current_pd_d;
+}
+
+pagedir_t *get_kernel_pagedir() {
+	return &kernel_pd_d;
+}
+
+void switch_pagedir(pagedir_t *pd) {
+	asm volatile("movl %0, %%cr3":: "r"(pd->phys_addr));
+	if (current_thread != 0) current_thread->current_pd_d = pd;
+}
+
+// ============================== //
+// Mapping and unmapping of pages //
+// ============================== //
+
+uint32_t pd_get_frame(void* vaddr) {
+	uint32_t pt = PT_OF_ADDR(vaddr);
+	uint32_t page = PAGE_OF_ADDR(vaddr);
+
+	pagetable_t *pd = ((size_t)vaddr >= K_HIGHHALF_ADDR ? &kernel_pd : current_pd);
+
+	if (!pd->page[pt] & PTE_PRESENT) return 0;
+	if (!current_pt[pt].page[page] & PTE_PRESENT) return 0;
+	return current_pt[pt].page[page] >> PTE_FRAME_SHIFT;
+}
+
+int pd_map_page(void* vaddr, uint32_t frame_id, bool rw) {
+	uint32_t pt = PT_OF_ADDR(vaddr);
+	uint32_t page = PAGE_OF_ADDR(vaddr);
+
+	ASSERT((size_t)vaddr < PD_MIRROR_ADDR);
+	
+	pagedir_t *pdd = ((size_t)vaddr >= K_HIGHHALF_ADDR || current_thread == 0
+							? &kernel_pd_d : current_thread->current_pd_d);
+	pagetable_t *pd = ((size_t)vaddr >= K_HIGHHALF_ADDR ? &kernel_pd : current_pd);
+	mutex_lock(&pdd->mutex);
+
+	if (!pd->page[pt] & PTE_PRESENT) {
+		uint32_t new_pt_frame = frame_alloc(1);
+		if (new_pt_frame == 0) {
+			mutex_unlock(&pdd->mutex);
+			return 1;	// OOM
+		}
+
+		current_pd->page[pt] = pd->page[pt] =
+			(new_pt_frame << PTE_FRAME_SHIFT) | PTE_PRESENT | PTE_RW;
+		invlpg(&current_pt[pt]);
+	}
+	current_pt[pt].page[page] =
+		(frame_id << PTE_FRAME_SHIFT)
+			| PTE_PRESENT
+			| ((size_t)vaddr < K_HIGHHALF_ADDR ? PTE_USER : PTE_GLOBAL)
+			| (rw ? PTE_RW : 0);
+	invlpg(vaddr);
+
+	mutex_unlock(&pdd->mutex);
+	return 0;
+} 
+
+void pd_unmap_page(void* vaddr) {
+	uint32_t pt = PT_OF_ADDR(vaddr);
+	uint32_t page = PAGE_OF_ADDR(vaddr);
+
+	pagetable_t *pd = ((size_t)vaddr >= K_HIGHHALF_ADDR ? &kernel_pd : current_pd);
+	// no need to lock the PD's mutex
+
+	if (!pd->page[pt] & PTE_PRESENT) return;
+	if (!current_pt[pt].page[page] & PTE_PRESENT) return;
+
+	current_pt[pt].page[page] = 0;
+	invlpg(vaddr);
+
+	// If the page table is completely empty we might want to free
+	// it, but we would actually lose a lot of time checking if
+	// the PT is really empty (since we don't store the
+	// number of used pages in each PT), so it's probably not worth it
+}
+
+// Creation and deletion of page directories
+
+pagedir_t *create_pagedir() {
+	uint32_t pd_phys = 0;
+	pagedir_t *pd = 0;
+	void* temp = 0;
+
+	pd_phys = frame_alloc(1);
+	if (pd_phys == 0) goto error;
+
+	pd = (pagedir_t*)malloc(sizeof(pagedir_t));
+	if (pd == 0) goto error;
+
+	temp = region_alloc(PAGE_SIZE, 0, 0);
+	if (temp == 0) goto error;
+
+	int error = pd_map_page(temp, pd_phys, true);
+	if (error) goto error;
+
+	pd->phys_addr = pd_phys * PAGE_SIZE;
+	pd->mutex = MUTEX_UNLOCKED;
+
+	// initialize PD with zeroes
+	pagetable_t *pt = (pagetable_t*)temp;
+	for (size_t i = 0; i < N_PAGES_IN_PT; i++) {
+		pt->page[i] = 0;
+	}
+	// use kernel page tables
+	for(size_t i = FIRST_KERNEL_PT; i < N_PAGES_IN_PT-1; i++) {
+		pt->page[i] = kernel_pd.page[i];
+	}
+	// set up mirroring
+	pt->page[N_PAGES_IN_PT-1] = pd->phys_addr | PTE_PRESENT | PTE_RW;
+
+	region_free_unmap(temp);
+
+	return pd;
+
+	error:
+	if (pd_phys != 0) frame_free(pd_phys, 1);
+	if (pd != 0) free(pd);
+	if (temp != 0) region_free(temp);
+	return 0;
+}
+
+void delete_pagedir(pagedir_t *pd) {
+	pagedir_t *restore_pd = get_current_pagedir();
+	if (restore_pd == pd) restore_pd = &kernel_pd_d;
+
+	// make a copy of page directory on the stack
+	switch_pagedir(pd);
+	pagetable_t backup;
+	for (size_t i = 0; i < N_PAGES_IN_PT; i++) {
+		backup.page[i] = current_pd->page[i];
+	}
+	switch_pagedir(restore_pd);
+	
+	// free the page tables
+	for (size_t i = 0; i < FIRST_KERNEL_PT; i++) {
+		if (backup.page[i] & PTE_PRESENT)
+			frame_free(backup.page[i] >> PTE_FRAME_SHIFT, 1);
+	}
+	// free the page directory page
+	uint32_t pd_phys = pd->phys_addr / PAGE_SIZE;
+	ASSERT(pd_phys == (backup.page[N_PAGES_IN_PT-1] >> PTE_FRAME_SHIFT));
+	frame_free(pd_phys, 1);
+	// free the pagedir_t structure
+	free(pd);
+
+	return;
+}
+
+/* vim: set ts=4 sw=4 tw=0 noet :*/