arch: i386: paging: add a proper paging API

Add a proper page control API. These functions allow the kernel to
directly map and unmap pages in the logical address space.

Signed-off-by: Danny Holman <dholman@gymli.org>

2 files changed, 140 insertions, 0 deletions

diff --git a/arch/i386/include/kernel/paging.h b/arch/i386/include/kernel/paging.h
new file mode 100644
index 0000000..c65718f
--- /dev/null
+++ b/arch/i386/include/kernel/paging.h
@@ -0,0 +1,52 @@
+#ifndef I386_PAGING_H
+#define I386_PAGING_H
+
+#include <kernel/isr.h>
+#include <stdint.h>
+
+#define PD_PRES         0x0001
+#define PD_RW           0x0002
+#define PD_USR          0x0004
+#define PD_PWT          0x0008
+#define PD_PCD          0x0010
+#define PD_ACC          0x0020
+#define PD_DIRTY        0x0040
+#define PD_PS           0x0080
+#define PD_GLOB         0x0100
+#define PD_PAT          0x1000
+
+#define ERR_PRESENT     0x1
+#define ERR_RW          0x2
+#define ERR_USER        0x4
+#define ERR_RESERVED    0x8
+#define ERR_INST        0x10
+
+#define BLOCK_SIZE 4096
+#define BLOCKS_PER_BUCKET 8
+#define BLOCK_ALIGN(addr) (((addr) & 0xFFFFF000) + 0x1000)
+
+#define SETBIT(x,i)     x[i/BLOCKS_PER_BUCKET] = x[i/BLOCKS_PER_BUCKET] | (1 << (i % BLOCKS_PER_BUCKET))
+#define CLEARBIT(x,i)   x[i/BLOCKS_PER_BUCKET] = x[i/BLOCKS_PER_BUCKET] & (~(1 << (i % BLOCKS_PER_BUCKET)))
+#define ISSET(x,i)      ((x[i/BLOCKS_PER_BUCKET] >> (i % BLOCKS_PER_BUCKET)) & 0x1)
+#define GETBUCKET(x,i)  (*((uint32_t*)&x[i/32]))
+
+#define PAGE_SIZE 4096
+
+struct page_frame {
+        int used;
+        uint32_t addr;
+};
+
+void load_page_dir(uint32_t pd_addr);
+void enable_paging(void);
+
+void paging_init();
+void page_fault_handler(struct isr_frame *frame);
+
+uint32_t get_paddr(uint32_t vaddr);
+uint32_t get_vaddr(uint32_t paddr);
+
+void map_page(uint32_t paddr, uint32_t vaddr, uint32_t flags);
+void unmap_page(uint32_t vaddr);
+
+#endif
diff --git a/arch/i386/kernel/paging.c b/arch/i386/kernel/paging.c
new file mode 100644
index 0000000..d8f72a3
--- /dev/null
+++ b/arch/i386/kernel/paging.c
@@ -0,0 +1,88 @@
+#include <kernel/paging.h>
+#include <kernel/io.h>
+#include <kernel/syscall.h>
+#include <kernel/string.h>
+#include <kernel/alloc.h>
+#include <stddef.h>
+
+extern int halt_catch_fire();
+extern uint32_t _kernel_start;
+extern uint32_t _kernel_end;
+static uint32_t *kstart = &_kernel_start;
+static uint32_t *kend = (uint32_t)(&_kernel_end) - 0xC0000000;
+
+static uint32_t page_directory[1024] __attribute__((aligned(PAGE_SIZE)));
+static uint32_t first_page_table[1024] __attribute__((aligned(PAGE_SIZE)));
+
+static int paging_enabled = 0;
+
+void paging_init(void) {
+        for (int i = 0; i < 1024; i++)
+                page_directory[i] = 0x00000002;
+
+        page_directory[1023] = ((uint32_t)&page_directory - 0xC0000000) | 3;
+        page_directory[0] = ((uint32_t)&first_page_table - 0xC0000000) | 3;
+        page_directory[768] = ((uint32_t)&first_page_table - 0xC0000000) | 3;
+        for (uint32_t i = kstart; i < kend; i += 4096) {
+                map_page(i, get_vaddr(i), 0x003);
+                mark_bitmap(i, 1);
+        }
+
+        map_page(0xB8000, 0xC03FF000, 0x003);
+        mark_bitmap(0xB8000, 1);
+
+        load_page_dir(((uint32_t)&page_directory) - 0xC0000000);
+        enable_paging();
+        paging_enabled = 1;
+        return;
+}
+
+void page_fault_handler(struct isr_frame *frame) {
+        kprintf("Page fault detected\n");
+        uint32_t errno = frame->errno;
+
+        uint32_t fault_addr;
+        __asm__ volatile("movl %%cr2, %0" : "=r"(fault_addr));
+        kprintf("Fault occured at address %x\n", fault_addr);
+        uint32_t present = errno & ERR_PRESENT;
+        uint32_t rw = errno & ERR_RW;
+        uint32_t user = errno & ERR_USER;
+        uint32_t reserved = errno & ERR_RESERVED;
+        uint32_t ifetch = errno & ERR_INST;
+        kprintf("Possible causes:\n");
+        if (!present) kprintf("\tPage not present\n");
+        if (rw || user) kprintf("\tPage is read only\n");
+        if (reserved) kprintf("\tOverwrote reserved bits\n");
+        if (ifetch) kprintf("\tInstruction fetch\n");
+        halt_catch_fire(frame);
+}
+
+uint32_t get_paddr(uint32_t vaddr) {
+        uint32_t pdindex = vaddr >> 22;
+        uint32_t ptindex = vaddr >> 12 & 0x03FF;
+
+        uint32_t *page_table = (page_directory[pdindex] + 0xC0000000 & 0xFFFFF000);
+        return (page_table[ptindex] & 0xFFFFF000) | (vaddr & 0x00000FFF);
+}
+
+uint32_t get_vaddr(uint32_t paddr) {
+        return paddr + 0xC0000000;
+}
+
+void map_page(uint32_t paddr, uint32_t vaddr, uint32_t flags) {
+        uint32_t pdindex = vaddr >> 22;
+        uint32_t ptindex = vaddr >> 12 & 0x03FF;
+
+        uint32_t *page_table = (page_directory[pdindex] + 0xC0000000 & 0xFFFFF000);
+        uint32_t *pte = (uint32_t*)(&page_table[ptindex]);
+        *pte |= paddr | (flags & 0xFFF) | 0x01;
+}
+
+void unmap_page(uint32_t vaddr) {
+        uint32_t pdindex = vaddr >> 22;
+        uint32_t ptindex = vaddr >> 12 & 0x03FF;
+
+        uint32_t *page_table = (page_directory[pdindex] + 0xC0000000 & 0xFFFFF000);
+        uint32_t *pte = (uint32_t*)(&page_table[ptindex]);
+        *pte &= 0;
+}