added first version of paging code

(only page_map() works for now)

arch/x86/include/asm/page.h

@@ -50,7 +50,7 @@
 /// Page map bits
 #define PAGE_MAP_BITS		10
 /// Number of page map indirections
-#define PAGE_MAP_LEVELS	2
+#define PAGE_LEVELS	2
 /// Mask the page address without page map flags
 #define PAGE_MASK		0xFFFFF000
 
@@ -93,11 +93,14 @@
 #define PG_BOOT			(1 << 9)
 
 
-/** @brief A single entry in a page map
+/** @brief Converts a virtual address to a physical
  *
- * Usually used as a pointer to a mapped page map entry.
+ * A non mapped virtual address causes a pagefault!
+ *
+ * @param addr Virtual address to convert
+ * @return physical address
  */
-typedef size_t page_entry_t;
+size_t page_virt_to_phys(size_t vir);
 
 /** @brief Initialize paging subsystem
  *
@@ -112,27 +115,19 @@ int page_init();
  *
  * @param viraddr
  * @param phyaddr
- * @param pages
- * @param flags
+ * @param npages
+ * @param bits
  * @return
  */
-int page_map(size_t viraddr, size_t phyaddr, size_t pages, size_t flags);
+int page_map(size_t viraddr, size_t phyaddr, size_t npages, size_t bits);
 
 /** @brief Unmap a continious region of pages
  *
  * @param viraddr
- * @param pages
+ * @param npages
  * @return
  */
-int page_unmap(size_t viraddr, size_t pages);
-
-/**  @brief Copy a single page frame
- *
- * @param dest
- * @param src
- * @return
- */
-int page_copy(size_t dest, size_t src);
+int page_unmap(size_t viraddr, size_t npages);
 
 /** @brief Copy a whole page map tree
  *
@@ -140,19 +135,12 @@ int page_copy(size_t dest, size_t src);
  * @param src
  * @return
  */
-int page_map_copy(page_entry_t *dest, page_entry_t *src);
+int page_map_copy(size_t *dest, size_t *src);
 
 /** @brief Free a whole page map tree
  *
  * @param map
  */
-int page_map_drop(page_entry_t *map);
-
-/** @brief Converts a virtual address to a physical
- *
- * @param viraddr Virtual address to convert
- * @return Physical address
- */
-size_t virt_to_phys(size_t viraddr);
+int page_map_drop(size_t *map);
 
 #endif

arch/x86/kernel/entry.asm

@@ -1,4 +1,4 @@
-;
+
 ; Copyright (c) 2010, Stefan Lankes, RWTH Aachen University
 ; All rights reserved.
 ;
@@ -318,22 +318,25 @@ ALIGN 4
 mb_info:
 	DD 0
 
-global boot_stack
 ALIGN 4096
+global boot_stack
 boot_stack:
 	TIMES (KERNEL_STACK_SIZE) DB 0xcd
 
 ; Bootstrap page tables are used during the initialization.
 ; These tables do a simple identity paging and will
 ; be replaced in page_init() by more fine-granular mappings.
-global boot_map
 ALIGN 4096
+global boot_map
 boot_map:
 boot_pgd:
+	DD boot_pgt + 0x103	; PG_GLOBAL | PG_RW | PG_PRESENT
+	times 1023 DD 0		; PAGE_MAP_ENTRIES - 1
+boot_pgt:
 	%assign i 0
-	%rep 1024
-	DD (i << 12) | 0x083
-	%assign i i+1
+	%rep 1024		; PAGE_MAP_ENTRIES
+	DD i        | 0x203	; PG_BOOT | PG_RW | PG_PRESENT
+	%assign i i + 4096	; PAGE_SIZE
 	%endrep
 
 ; add some hints to the ELF file

arch/x86/mm/Makefile

@@ -0,0 +1,4 @@
+C_source := page.c
+MODULE := arch_x86_mm
+
+include $(TOPDIR)/Makefile.inc

arch/x86/mm/page.c

@@ -0,0 +1,238 @@
+/*
+ * Copyright (c) 2010, Stefan Lankes, RWTH Aachen University
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *    * Redistributions of source code must retain the above copyright
+ *      notice, this list of conditions and the following disclaimer.
+ *    * Redistributions in binary form must reproduce the above copyright
+ *      notice, this list of conditions and the following disclaimer in the
+ *      documentation and/or other materials provided with the distribution.
+ *    * Neither the name of the University nor the names of its contributors
+ *      may be used to endorse or promote products derived from this
+ *      software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE FOR ANY
+ * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <eduos/stdio.h>
+#include <eduos/memory.h>
+#include <eduos/errno.h>
+#include <eduos/string.h>
+
+#include <asm/irq.h>
+#include <asm/page.h>
+#include <asm/io.h>
+
+/* Note that linker symbols are not variables, they have no memory
+ * allocated for maintaining a value, rather their address is their value. */
+extern const void kernel_start;
+extern const void kernel_end;
+
+/** This PGD table is initialized in entry.asm */
+extern size_t boot_map[PAGE_MAP_ENTRIES];
+
+/** A self-reference enables direct access to all page tables */
+static size_t* self[PAGE_LEVELS] = {
+		(size_t *) PAGE_MAP_PGT, (size_t *) PAGE_MAP_PGD
+};
+
+#define self_child(lvl, vpn)	&self[lvl-1][vpn<<PAGE_MAP_BITS]
+#define self_parent(lvl, vpn)	&self[lvl+1][vpn>>PAGE_MAP_BITS]
+
+/** @todo Does't handle huge pages for now 
+ *  @todo This will cause a pagefaut if addr isn't mapped! */
+size_t page_virt_to_phys(size_t addr)
+{
+	size_t vpn   = addr >> PAGE_BITS;	// virtual page number
+	size_t entry = self[0][vpn];		// page table entry 
+	size_t off   = addr  & ~PAGE_MASK;	// offset within page
+	size_t phy   = entry &  PAGE_MASK;	// physical page frame number
+
+	return phy | off;
+}
+
+int page_map(size_t viraddr, size_t phyaddr, size_t npages, size_t bits)
+{
+	int lvl;
+	long vpn = viraddr >> PAGE_BITS;
+	long first[PAGE_LEVELS], last[PAGE_LEVELS];	// index boundaries for self-mapping
+
+	for (lvl=0; lvl<PAGE_LEVELS; lvl++) {
+		first[lvl] = (vpn         ) >> (lvl * PAGE_MAP_BITS);
+		last[lvl]  = (vpn + npages) >> (lvl * PAGE_MAP_BITS);
+	}
+
+	/* We start now iterating through the entries
+	 * beginning at the root table (PGD) */
+	for (lvl=PAGE_LEVELS-1; lvl>=0; lvl--) {
+		for (vpn=first[lvl]; vpn<=last[lvl]; vpn++) {
+			if (lvl) { /* PML4, PDPT, PGD */	
+				if (self[lvl][vpn] & PG_PRESENT) {
+					/* There already an existing table which only allows
+					 * kernel accesses. We need to copy the table to create
+					 * private copy for the user space process */
+					if (!(self[lvl][vpn] & PG_USER) && (bits & PG_USER)) {
+						size_t phyaddr = get_pages(1);
+						if (BUILTIN_EXPECT(!phyaddr, 0))
+							return -ENOMEM;
+
+						/* Copy old table contents to new one.
+						 * We temporarily use page zero for this
+						 * by mapping the new table to this address. */
+						page_map(0, phyaddr, 1, PG_RW | PG_PRESENT);
+						memcpy(0, self_child(lvl, vpn), PAGE_SIZE);
+
+						/* Update table by replacing address and altering flags */
+						self[lvl][vpn] &= ~(PAGE_MASK | PG_GLOBAL);
+						self[lvl][vpn] |=     phyaddr | PG_USER;
+
+						/* We only need to flush the self-mapped table.
+						 * TLB entries mapped by this table remain valid
+						 * because we only made an identical copy. */
+						tlb_flush_one_page((size_t) self_child(lvl, vpn));
+					}
+				}
+				else {
+					/* There's no table available which covers the region.
+					 * Therefore we need to create a new empty table. */
+					size_t phyaddr = get_pages(1);
+					if (BUILTIN_EXPECT(!phyaddr, 0))
+						return -ENOMEM;
+
+					/* Reference the new table in the parent */
+					self[lvl][vpn] = phyaddr | bits;
+
+					/* Fill new table with zeros */
+					memset(self_child(lvl, vpn), 0, PAGE_SIZE);
+				}
+			}
+			else { /* PGT */
+				if (self[lvl][vpn] & PG_PRESENT)
+					tlb_flush_one_page(vpn << PAGE_BITS);
+
+				self[lvl][vpn] = phyaddr | bits;
+				phyaddr += PAGE_SIZE;
+			}
+		}
+	}
+
+	return 0;
+}
+
+int page_unmap(size_t viraddr, size_t npages)
+{
+	int lvl;
+	long vpn = viraddr >> PAGE_BITS;
+	long first[PAGE_LEVELS], last[PAGE_LEVELS];	// index boundaries for self-mapping
+
+	for (lvl=0; lvl<PAGE_LEVELS; lvl++) {
+		first[lvl] = (vpn         ) >> (lvl * PAGE_MAP_BITS);
+		last[lvl]  = (vpn + npages) >> (lvl * PAGE_MAP_BITS);
+	}
+
+	/* We start now iterating through the entries
+	 * beginning at the root table (PGD) */
+	for (lvl=PAGE_LEVELS-1; lvl>=0; lvl--) {
+		for (vpn=first[lvl]; vpn<=last[lvl]; vpn++) {
+			if (lvl) { /* PML4, PDPT, PGD */	
+
+			}
+			else { /* PGT */
+
+			}
+		}
+	}
+
+	return 0;
+}
+
+int page_map_drop(size_t *map)
+{
+	int lvl;
+	long vpn;
+
+	/* We start now iterating through the entries
+	 * beginning at the root table (PGD) */
+	for (lvl=PAGE_LEVELS-1; lvl>=0; lvl--) {
+		for (vpn=0; vpn<PAGE_MAP_ENTRIES; vpn++) {
+			if (lvl) { /* PML4, PDPT, PGD */	
+
+			}
+			else { /* PGT */
+
+			}
+		}
+	}
+
+	return 0;
+}
+
+int page_map_copy(size_t *dest, size_t *src)
+{
+	int lvl;
+	long vpn;
+
+	/* We start now iterating through the entries
+	 * beginning at the root table (PGD) */
+	for (lvl=PAGE_LEVELS-1; lvl>=0; lvl--) {
+		for (vpn=0; vpn<PAGE_MAP_ENTRIES; vpn++) {
+			if (lvl) { /* PML4, PDPT, PGD */	
+
+			}
+			else { /* PGT */
+
+			}
+		}
+	}
+
+	return 0;
+}
+
+void page_fault_handler(struct state *s)
+{
+	size_t viraddr = read_cr2();
+
+	kprintf("Page Fault Exception (%d) at cs:ip = %#x:%#lx, address = %#lx\n",
+		s->int_no, s->cs, s->eip, viraddr);
+
+	outportb(0x20, 0x20);
+
+	while(1) HALT;
+}
+
+int page_init()
+{
+	size_t npages;
+
+	// replace default pagefault handler
+	irq_uninstall_handler(14);
+	irq_install_handler(14, page_fault_handler);
+
+	// create self-reference
+	boot_map[PAGE_MAP_ENTRIES-1] = (size_t) &boot_map | PG_PRESENT | PG_RW;
+
+	// map kernel
+	npages = PAGE_FLOOR((size_t) &kernel_end - (size_t) &kernel_start) >> PAGE_BITS;
+	page_map((size_t) &kernel_start, (size_t) &kernel_start, npages, PG_PRESENT | PG_RW | PG_GLOBAL);
+
+#ifdef CONFIG_VGA
+	// map video memory
+	page_map(VIDEO_MEM_ADDR, VIDEO_MEM_ADDR, 1, PG_PCD | PG_PRESENT | PG_RW);
+#endif
+
+	// flush TLB to apply new mappings
+	flush_tlb();
+
+	return 0;
+}

kernel/main.c

@@ -100,12 +100,12 @@ static int eduos_init(void)
 	// initialize .bss section
 	memset((void*)&bss_start, 0x00, ((size_t) &bss_end - (size_t) &bss_start));
 
-	memory_init();
 	system_init();
 	irq_init();
 	timer_init();
 	koutput_init();
 	multitasking_init();
+	memory_init();
 
 	return 0;
 }

mm/memory.c

@@ -230,10 +230,11 @@ int memory_init(void)
 	}
 
 	// enable paging and map SMP, VGA, Multiboot modules etc.
-	/*ret = page_init();
-	if (BUILTIN_EXPECT(ret, 0))
+	ret = page_init();
+	if (BUILTIN_EXPECT(ret, 0)) {
+		kputs("Failed to initialize paging!\n");
 		return ret;
-	*/
+	}
 
 	return ret;
 }