Basic MMU usage

core/main.c

@@ -7,12 +7,14 @@
 #include "klibc.h"
 #include "mem.h"
 #include "multiboot.h"
+#include "paging.h"
 #include "pit.h"
 #include "serial.h"
 #include "stdarg.h"
 #ifdef RUN_TEST
 #include "test.h"
 #endif
+#include "types.h"
 #include "vga.h"
 
 #define CHECK_FLAG(flags, bit) ((flags) & (1 << (bit)))
@@ -59,7 +61,9 @@ void kmain(unsigned long magic, unsigned long addr)
     }
 
     printf("Setting up Pagination\n");
-    memSetup(upper_mem);
+    paddr_t lastUserByMem;
+    memSetup(upper_mem, &lastUserByMem);
+    pagingSetup(lastUserByMem);
 
     printf("Setting up IRQ handlers\n");
     irqSetRoutine(IRQ_KEYBOARD, keyboard_handler);

core/mem.c

@@ -9,22 +9,23 @@ static struct mem_desc *used_page;
 static unsigned long bottom_mem;
 static unsigned long top_mem;
 
-int memSetup(unsigned long upper_mem)
+int memSetup(paddr_t upperMem, paddr_t * lastUsedOut)
 {
 	// Align upper mem (in kB) on page size even if it does loose a page
-	upper_mem = ALIGN_DOWN(upper_mem, PAGE_SIZE / 1024);
+	upperMem = ALIGN_DOWN(upperMem, PAGE_SIZE / 1024);
 
-	printf("Available Mem from %d to %d \n", &__ld_kernel_end, upper_mem * 1024);
+	printf("Available Mem from %d to %d \n", &__ld_kernel_end, upperMem * 1024);
 	// Memory description is stored after the kernel. We need some place to store it
 	unsigned long memdesc_end =
 	    (unsigned long)page_desc +
-	    ((upper_mem) / (PAGE_SIZE / 1024)) * sizeof(struct mem_desc);
+	    ((upperMem) / (PAGE_SIZE / 1024)) * sizeof(struct mem_desc);
 	uint lastUsed = (memdesc_end >> PAGE_SHIFT) + 1;
 	list_init(free_page);
 	list_init(used_page);
 	bottom_mem = lastUsed;
-	top_mem    = upper_mem * 1024;
-	for (uint i = 0; i < (upper_mem / (PAGE_SIZE / 1024)); i++) {
+	*lastUsedOut = memdesc_end;
+	top_mem    = upperMem * 1024;
+	for (uint i = 0; i < (upperMem / (PAGE_SIZE / 1024)); i++) {
 		struct mem_desc *mem = &page_desc[i];
 		if (i < lastUsed) {
 			mem->ref = 1;

core/mem.h

@@ -17,7 +17,7 @@ struct mem_desc{
 };
 
 
-int memSetup(unsigned long upper_mem);
+int memSetup(paddr_t upperMem, paddr_t *lastUsed);
 paddr_t allocPhyPage(void);
 int unrefPhyPage(paddr_t addr);
 int refPhyPage(paddr_t addr);

core/paging.c

@@ -0,0 +1,118 @@
+#include "klibc.h"
+#include "mem.h"
+#include "stdarg.h"
+
+// In a Vaddr, 10 first bit (MSB) are the index in the Page Directory. A Page Directory Entry point to a Page Table.
+// The 10 next bits are then an index in this Page Table. A Page Table Entry then point to a physical address at which is added the remaining 12 bits.
+// So they are 1024 entry in the PD, each of them pointing to a PT of 1024 entry. Each PTE pointing to 4K page.
+// First address (up to page_desc from mem.c) are mapped such as Paddr == Vaddr.
+// To make PD always accessible a (x86?) trick is used : The mirroring. A given entry N in the PD point to the PD (this is possible because PDE very looks like PTE in x86).
+// So N << (10 + 12 = 4Mo) point to the Paddr of PD. Then, accessing N * 4Mo + I * 4Ko is accessing the PT of the Ieme entry in the PD (as MMU take the PD pointed by the PDE number N like a PT).
+// More particularly, accessing N * 4Mo + N * 4ko is accessing the PD.
+//
+// PD is at Vaddr N * 4Mo and take 4ko. Each PT are allocated dynamically.
+// Just make sure that N have not been used by identity mapping
+
+#define PT_SHIFT 12
+#define PTE_MASK 0x3ff //10bits
+#define PD_SHIFT 22
+#define PD_MIRROR_PAGE_IDX 1023
+
+struct pde {
+	uint32_t present : 1;
+	uint32_t write : 1;         // 0 read - 1 RW
+	uint32_t user : 1;          // 0 supervisor - 1 user
+	uint32_t write_through : 1; // 0 write-back - 1 write_through
+	uint32_t cache_disable : 1;
+	uint32_t access : 1; // have been accessed
+	uint32_t zero : 1;   // Not used
+	uint32_t size : 1;   // 0 for 4Kb 1 for 4Mb
+	uint32_t ignored : 1;
+	uint32_t available : 3;
+	uint32_t pt_addr : 20;
+} __attribute__((packed));
+
+struct pte {
+	uint32_t present : 1;
+	uint32_t write : 1;         // 0 read - 1 RW
+	uint32_t user : 1;          // 0 supervisor - 1 user
+	uint32_t write_through : 1; // 0 write-back - 1 write_through
+	uint32_t cache_disable : 1;
+	uint32_t access : 1; // have been accessed
+	uint32_t dirty : 1;  // if set, indicates that page has been written to. This flag is
+			     // not updated by the CPU, and once set will not unset itself.
+	uint32_t zero : 1;   // if PAT is supported, shall indicate the memory type. Otherwise,
+			     // it must be 0.
+	uint32_t global : 1; // if set, prevents the TLB from updating the address in its cache
+			     // if CR3 is reset. Note, that the page global enable bit in CR4
+			     // must be set to enable this feature.
+	uint32_t available : 3;
+	uint32_t paddr : 20;
+} __attribute__((packed));
+
+struct pdbr {
+	uint32_t zero1 : 3;          // reserved
+	uint32_t write_through : 1;  // 0 write-back - 1 write-through
+	uint32_t cache_disabled : 1; // 1=cache disabled
+	uint32_t zero2 : 7;          // reserved
+	uint32_t pd_paddr : 20;
+} __attribute__((packed));
+
+static inline void __native_flush_tlb_single(unsigned long addr)
+{
+	asm volatile("invlpg (%0)" ::"r"(addr) : "memory");
+}
+
+int pagingSetup(paddr_t upperKernelAddr)
+{
+	struct pdbr cr3;
+
+	// x86 got 1024 of pde for 4Byte each: 4ko !
+	struct pde *pd = (struct pde *)allocPhyPage();
+
+	memset(pd, 0, PAGE_SIZE);
+	memset(&cr3, 0x0, sizeof(struct pdbr));
+
+	cr3.pd_paddr = ((paddr_t)pd) >> 12;
+
+	// MMU not enabled for the moment. No need to use mirroring
+	// Identity mapping up to upperKernelAddr
+	for (paddr_t i = 0; i < upperKernelAddr; i += PAGE_SIZE) {
+		uint pdEntry = i >> (PD_SHIFT);
+		uint ptEntry = (i >> PT_SHIFT ) & PTE_MASK;
+		struct pte *pt;
+		if (pd[pdEntry].present){
+			pt = (struct pte *)(pd[pdEntry].pt_addr << PT_SHIFT);
+			refPhyPage((paddr_t)pt);
+		} else {
+			pt = (struct pte *)allocPhyPage();
+
+			memset(pt, 0, PAGE_SIZE);
+			pd[pdEntry].present = 1;
+			pd[pdEntry].write = 1;
+			pd[pdEntry].pt_addr =  ((paddr_t)pt >> PT_SHIFT);
+		}
+
+		pt[ptEntry].present = 1;
+		pt[ptEntry].write = 1; //TODO set Kernel code as RO
+		pt[ptEntry].paddr = i >> PAGE_SHIFT;
+	}
+
+	// Setup mirroring
+	pd[PD_MIRROR_PAGE_IDX].present = 1;
+	pd[PD_MIRROR_PAGE_IDX].write = 1;
+	pd[PD_MIRROR_PAGE_IDX].pt_addr = ((paddr_t)pd >> PT_SHIFT);
+
+
+	// Loading of the PDBR in the MMU:
+	asm volatile ("movl %0,%%cr3\n\t"
+			"movl %%cr0,%%eax\n\t"
+			"orl $0x80010000, %%eax\n\t" /* bit 31 | bit 16 */
+			"movl %%eax,%%cr0\n\t"
+			"jmp 1f\n\t"
+			"1:\n\t"
+			"movl $2f, %%eax\n\t"
+			"jmp *%%eax\n\t"
+			"2:\n\t" ::"r"(cr3):"memory","eax");
+	return 0;
+}

core/paging.h

@@ -0,0 +1,4 @@
+#pragma once
+#include "types.h"
+
+int pagingSetup(paddr_t upperKernelAddr);