Lab 2

GNUmakefile

@@ -67,6 +67,7 @@ endif
 GDBPORT	:= $(shell expr `id -u` % 5000 + 25000)
 
 CC	:= $(GCCPREFIX)gcc -pipe
+GDB	:= $(GCCPREFIX)gdb
 AS	:= $(GCCPREFIX)as
 AR	:= $(GCCPREFIX)ar
 LD	:= $(GCCPREFIX)ld
@@ -148,7 +149,7 @@ QEMUOPTS += $(QEMUEXTRA)
 	sed "s/localhost:1234/localhost:$(GDBPORT)/" < $^ > $@
 
 gdb:
-	gdb -n -x .gdbinit
+	$(GDB) -n -x .gdbinit
 
 pre-qemu: .gdbinit
 

conf/lab.mk

@@ -1,2 +1,2 @@
-LAB=1
-PACKAGEDATE=Thu Aug 30 15:16:04 EDT 2018
+LAB=2
+PACKAGEDATE=Wed Sep 12 14:51:29 EDT 2018

grade-lab2

@@ -0,0 +1,28 @@
+#!/usr/bin/env python
+
+from gradelib import *
+
+r = Runner(save("jos.out"),
+           stop_breakpoint("readline"))
+
+@test(0, "running JOS")
+def test_jos():
+    r.run_qemu()
+
+@test(20, "Physical page allocator", parent=test_jos)
+def test_check_page_alloc():
+    r.match(r"check_page_alloc\(\) succeeded!")
+
+@test(20, "Page management", parent=test_jos)
+def test_check_page():
+    r.match(r"check_page\(\) succeeded!")
+
+@test(20, "Kernel page directory", parent=test_jos)
+def test_check_kern_pgdir():
+    r.match(r"check_kern_pgdir\(\) succeeded!")
+
+@test(10, "Page management 2", parent=test_jos)
+def test_check_page_installed_pgdir():
+    r.match(r"check_page_installed_pgdir\(\) succeeded!")
+
+run_tests()

inc/memlayout.h

@@ -143,5 +143,46 @@
 typedef uint32_t pte_t;
 typedef uint32_t pde_t;
 
+#if JOS_USER
+/*
+ * The page directory entry corresponding to the virtual address range
+ * [UVPT, UVPT + PTSIZE) points to the page directory itself.  Thus, the page
+ * directory is treated as a page table as well as a page directory.
+ *
+ * One result of treating the page directory as a page table is that all PTEs
+ * can be accessed through a "virtual page table" at virtual address UVPT (to
+ * which uvpt is set in lib/entry.S).  The PTE for page number N is stored in
+ * uvpt[N].  (It's worth drawing a diagram of this!)
+ *
+ * A second consequence is that the contents of the current page directory
+ * will always be available at virtual address (UVPT + (UVPT >> PGSHIFT)), to
+ * which uvpd is set in lib/entry.S.
+ */
+extern volatile pte_t uvpt[];     // VA of "virtual page table"
+extern volatile pde_t uvpd[];     // VA of current page directory
+#endif
+
+/*
+ * Page descriptor structures, mapped at UPAGES.
+ * Read/write to the kernel, read-only to user programs.
+ *
+ * Each struct PageInfo stores metadata for one physical page.
+ * Is it NOT the physical page itself, but there is a one-to-one
+ * correspondence between physical pages and struct PageInfo's.
+ * You can map a struct PageInfo * to the corresponding physical address
+ * with page2pa() in kern/pmap.h.
+ */
+struct PageInfo {
+	// Next page on the free list.
+	struct PageInfo *pp_link;
+
+	// pp_ref is the count of pointers (usually in page table entries)
+	// to this page, for pages allocated using page_alloc.
+	// Pages allocated at boot time using pmap.c's
+	// boot_alloc do not have valid reference count fields.
+
+	uint16_t pp_ref;
+};
+
 #endif /* !__ASSEMBLER__ */
 #endif /* !JOS_INC_MEMLAYOUT_H */

kern/init.c

@@ -6,18 +6,9 @@
 
 #include <kern/monitor.h>
 #include <kern/console.h>
+#include <kern/pmap.h>
+#include <kern/kclock.h>
 
-// Test the stack backtrace function (lab 1 only)
-void
-test_backtrace(int x)
-{
-	cprintf("entering test_backtrace %d\n", x);
-	if (x > 0)
-		test_backtrace(x-1);
-	else
-		mon_backtrace(0, 0, 0);
-	cprintf("leaving test_backtrace %d\n", x);
-}
 
 void
 i386_init(void)
@@ -35,8 +26,8 @@ i386_init(void)
 
 	cprintf("6828 decimal is %o octal!\n", 6828);
 
-	// Test the stack backtrace function (lab 1 only)
-	test_backtrace(5);
+	// Lab 2 memory management initialization functions
+	mem_init();
 
 	// Drop into the kernel monitor.
 	while (1)

kern/kclock.c

@@ -0,0 +1,22 @@
+/* See COPYRIGHT for copyright information. */
+
+/* Support for reading the NVRAM from the real-time clock. */
+
+#include <inc/x86.h>
+
+#include <kern/kclock.h>
+
+
+unsigned
+mc146818_read(unsigned reg)
+{
+	outb(IO_RTC, reg);
+	return inb(IO_RTC+1);
+}
+
+void
+mc146818_write(unsigned reg, unsigned datum)
+{
+	outb(IO_RTC, reg);
+	outb(IO_RTC+1, datum);
+}

kern/kclock.h

@@ -0,0 +1,29 @@
+/* See COPYRIGHT for copyright information. */
+
+#ifndef JOS_KERN_KCLOCK_H
+#define JOS_KERN_KCLOCK_H
+#ifndef JOS_KERNEL
+# error "This is a JOS kernel header; user programs should not #include it"
+#endif
+
+#define	IO_RTC		0x070		/* RTC port */
+
+#define	MC_NVRAM_START	0xe	/* start of NVRAM: offset 14 */
+#define	MC_NVRAM_SIZE	50	/* 50 bytes of NVRAM */
+
+/* NVRAM bytes 7 & 8: base memory size */
+#define NVRAM_BASELO	(MC_NVRAM_START + 7)	/* low byte; RTC off. 0x15 */
+#define NVRAM_BASEHI	(MC_NVRAM_START + 8)	/* high byte; RTC off. 0x16 */
+
+/* NVRAM bytes 9 & 10: extended memory size (between 1MB and 16MB) */
+#define NVRAM_EXTLO	(MC_NVRAM_START + 9)	/* low byte; RTC off. 0x17 */
+#define NVRAM_EXTHI	(MC_NVRAM_START + 10)	/* high byte; RTC off. 0x18 */
+
+/* NVRAM bytes 38 and 39: extended memory size (between 16MB and 4G) */
+#define NVRAM_EXT16LO	(MC_NVRAM_START + 38)	/* low byte; RTC off. 0x34 */
+#define NVRAM_EXT16HI	(MC_NVRAM_START + 39)	/* high byte; RTC off. 0x35 */
+
+unsigned mc146818_read(unsigned reg);
+void mc146818_write(unsigned reg, unsigned datum);
+
+#endif	// !JOS_KERN_KCLOCK_H

kern/pmap.c

@@ -0,0 +1,841 @@
+/* See COPYRIGHT for copyright information. */
+
+#include <inc/x86.h>
+#include <inc/mmu.h>
+#include <inc/error.h>
+#include <inc/string.h>
+#include <inc/assert.h>
+
+#include <kern/pmap.h>
+#include <kern/kclock.h>
+
+// These variables are set by i386_detect_memory()
+size_t npages;			// Amount of physical memory (in pages)
+static size_t npages_basemem;	// Amount of base memory (in pages)
+
+// These variables are set in mem_init()
+pde_t *kern_pgdir;		// Kernel's initial page directory
+struct PageInfo *pages;		// Physical page state array
+static struct PageInfo *page_free_list;	// Free list of physical pages
+
+
+// --------------------------------------------------------------
+// Detect machine's physical memory setup.
+// --------------------------------------------------------------
+
+static int
+nvram_read(int r)
+{
+	return mc146818_read(r) | (mc146818_read(r + 1) << 8);
+}
+
+static void
+i386_detect_memory(void)
+{
+	size_t basemem, extmem, ext16mem, totalmem;
+
+	// Use CMOS calls to measure available base & extended memory.
+	// (CMOS calls return results in kilobytes.)
+	basemem = nvram_read(NVRAM_BASELO);
+	extmem = nvram_read(NVRAM_EXTLO);
+	ext16mem = nvram_read(NVRAM_EXT16LO) * 64;
+
+	// Calculate the number of physical pages available in both base
+	// and extended memory.
+	if (ext16mem)
+		totalmem = 16 * 1024 + ext16mem;
+	else if (extmem)
+		totalmem = 1 * 1024 + extmem;
+	else
+		totalmem = basemem;
+
+	npages = totalmem / (PGSIZE / 1024);
+	npages_basemem = basemem / (PGSIZE / 1024);
+
+	cprintf("Physical memory: %uK available, base = %uK, extended = %uK\n",
+		totalmem, basemem, totalmem - basemem);
+}
+
+
+// --------------------------------------------------------------
+// Set up memory mappings above UTOP.
+// --------------------------------------------------------------
+
+static void boot_map_region(pde_t *pgdir, uintptr_t va, size_t size, physaddr_t pa, int perm);
+static void check_page_free_list(bool only_low_memory);
+static void check_page_alloc(void);
+static void check_kern_pgdir(void);
+static physaddr_t check_va2pa(pde_t *pgdir, uintptr_t va);
+static void check_page(void);
+static void check_page_installed_pgdir(void);
+
+// This simple physical memory allocator is used only while JOS is setting
+// up its virtual memory system.  page_alloc() is the real allocator.
+//
+// If n>0, allocates enough pages of contiguous physical memory to hold 'n'
+// bytes.  Doesn't initialize the memory.  Returns a kernel virtual address.
+//
+// If n==0, returns the address of the next free page without allocating
+// anything.
+//
+// If we're out of memory, boot_alloc should panic.
+// This function may ONLY be used during initialization,
+// before the page_free_list list has been set up.
+static void *
+boot_alloc(uint32_t n)
+{
+	static char *nextfree;	// virtual address of next byte of free memory
+	char *result;
+
+	// Initialize nextfree if this is the first time.
+	// 'end' is a magic symbol automatically generated by the linker,
+	// which points to the end of the kernel's bss segment:
+	// the first virtual address that the linker did *not* assign
+	// to any kernel code or global variables.
+	if (!nextfree) {
+		extern char end[];
+		nextfree = ROUNDUP((char *) end, PGSIZE);
+	}
+
+	// Allocate a chunk large enough to hold 'n' bytes, then update
+	// nextfree.  Make sure nextfree is kept aligned
+	// to a multiple of PGSIZE.
+	//
+	// LAB 2: Your code here.
+
+	return NULL;
+}
+
+// Set up a two-level page table:
+//    kern_pgdir is its linear (virtual) address of the root
+//
+// This function only sets up the kernel part of the address space
+// (ie. addresses >= UTOP).  The user part of the address space
+// will be set up later.
+//
+// From UTOP to ULIM, the user is allowed to read but not write.
+// Above ULIM the user cannot read or write.
+void
+mem_init(void)
+{
+	uint32_t cr0;
+	size_t n;
+
+	// Find out how much memory the machine has (npages & npages_basemem).
+	i386_detect_memory();
+
+	// Remove this line when you're ready to test this function.
+	panic("mem_init: This function is not finished\n");
+
+	//////////////////////////////////////////////////////////////////////
+	// create initial page directory.
+	kern_pgdir = (pde_t *) boot_alloc(PGSIZE);
+	memset(kern_pgdir, 0, PGSIZE);
+
+	//////////////////////////////////////////////////////////////////////
+	// Recursively insert PD in itself as a page table, to form
+	// a virtual page table at virtual address UVPT.
+	// (For now, you don't have understand the greater purpose of the
+	// following line.)
+
+	// Permissions: kernel R, user R
+	kern_pgdir[PDX(UVPT)] = PADDR(kern_pgdir) | PTE_U | PTE_P;
+
+	//////////////////////////////////////////////////////////////////////
+	// Allocate an array of npages 'struct PageInfo's and store it in 'pages'.
+	// The kernel uses this array to keep track of physical pages: for
+	// each physical page, there is a corresponding struct PageInfo in this
+	// array.  'npages' is the number of physical pages in memory.  Use memset
+	// to initialize all fields of each struct PageInfo to 0.
+	// Your code goes here:
+
+
+	//////////////////////////////////////////////////////////////////////
+	// Now that we've allocated the initial kernel data structures, we set
+	// up the list of free physical pages. Once we've done so, all further
+	// memory management will go through the page_* functions. In
+	// particular, we can now map memory using boot_map_region
+	// or page_insert
+	page_init();
+
+	check_page_free_list(1);
+	check_page_alloc();
+	check_page();
+
+	//////////////////////////////////////////////////////////////////////
+	// Now we set up virtual memory
+
+	//////////////////////////////////////////////////////////////////////
+	// Map 'pages' read-only by the user at linear address UPAGES
+	// Permissions:
+	//    - the new image at UPAGES -- kernel R, user R
+	//      (ie. perm = PTE_U | PTE_P)
+	//    - pages itself -- kernel RW, user NONE
+	// Your code goes here:
+
+	//////////////////////////////////////////////////////////////////////
+	// Use the physical memory that 'bootstack' refers to as the kernel
+	// stack.  The kernel stack grows down from virtual address KSTACKTOP.
+	// We consider the entire range from [KSTACKTOP-PTSIZE, KSTACKTOP)
+	// to be the kernel stack, but break this into two pieces:
+	//     * [KSTACKTOP-KSTKSIZE, KSTACKTOP) -- backed by physical memory
+	//     * [KSTACKTOP-PTSIZE, KSTACKTOP-KSTKSIZE) -- not backed; so if
+	//       the kernel overflows its stack, it will fault rather than
+	//       overwrite memory.  Known as a "guard page".
+	//     Permissions: kernel RW, user NONE
+	// Your code goes here:
+
+	//////////////////////////////////////////////////////////////////////
+	// Map all of physical memory at KERNBASE.
+	// Ie.  the VA range [KERNBASE, 2^32) should map to
+	//      the PA range [0, 2^32 - KERNBASE)
+	// We might not have 2^32 - KERNBASE bytes of physical memory, but
+	// we just set up the mapping anyway.
+	// Permissions: kernel RW, user NONE
+	// Your code goes here:
+
+	// Check that the initial page directory has been set up correctly.
+	check_kern_pgdir();
+
+	// Switch from the minimal entry page directory to the full kern_pgdir
+	// page table we just created.	Our instruction pointer should be
+	// somewhere between KERNBASE and KERNBASE+4MB right now, which is
+	// mapped the same way by both page tables.
+	//
+	// If the machine reboots at this point, you've probably set up your
+	// kern_pgdir wrong.
+	lcr3(PADDR(kern_pgdir));
+
+	check_page_free_list(0);
+
+	// entry.S set the really important flags in cr0 (including enabling
+	// paging).  Here we configure the rest of the flags that we care about.
+	cr0 = rcr0();
+	cr0 |= CR0_PE|CR0_PG|CR0_AM|CR0_WP|CR0_NE|CR0_MP;
+	cr0 &= ~(CR0_TS|CR0_EM);
+	lcr0(cr0);
+
+	// Some more checks, only possible after kern_pgdir is installed.
+	check_page_installed_pgdir();
+}
+
+// --------------------------------------------------------------
+// Tracking of physical pages.
+// The 'pages' array has one 'struct PageInfo' entry per physical page.
+// Pages are reference counted, and free pages are kept on a linked list.
+// --------------------------------------------------------------
+
+//
+// Initialize page structure and memory free list.
+// After this is done, NEVER use boot_alloc again.  ONLY use the page
+// allocator functions below to allocate and deallocate physical
+// memory via the page_free_list.
+//
+void
+page_init(void)
+{
+	// The example code here marks all physical pages as free.
+	// However this is not truly the case.  What memory is free?
+	//  1) Mark physical page 0 as in use.
+	//     This way we preserve the real-mode IDT and BIOS structures
+	//     in case we ever need them.  (Currently we don't, but...)
+	//  2) The rest of base memory, [PGSIZE, npages_basemem * PGSIZE)
+	//     is free.
+	//  3) Then comes the IO hole [IOPHYSMEM, EXTPHYSMEM), which must
+	//     never be allocated.
+	//  4) Then extended memory [EXTPHYSMEM, ...).
+	//     Some of it is in use, some is free. Where is the kernel
+	//     in physical memory?  Which pages are already in use for
+	//     page tables and other data structures?
+	//
+	// Change the code to reflect this.
+	// NB: DO NOT actually touch the physical memory corresponding to
+	// free pages!
+	size_t i;
+	for (i = 0; i < npages; i++) {
+		pages[i].pp_ref = 0;
+		pages[i].pp_link = page_free_list;
+		page_free_list = &pages[i];
+	}
+}
+
+//
+// Allocates a physical page.  If (alloc_flags & ALLOC_ZERO), fills the entire
+// returned physical page with '\0' bytes.  Does NOT increment the reference
+// count of the page - the caller must do these if necessary (either explicitly
+// or via page_insert).
+//
+// Be sure to set the pp_link field of the allocated page to NULL so
+// page_free can check for double-free bugs.
+//
+// Returns NULL if out of free memory.
+//
+// Hint: use page2kva and memset
+struct PageInfo *
+page_alloc(int alloc_flags)
+{
+	// Fill this function in
+	return 0;
+}
+
+//
+// Return a page to the free list.
+// (This function should only be called when pp->pp_ref reaches 0.)
+//
+void
+page_free(struct PageInfo *pp)
+{
+	// Fill this function in
+	// Hint: You may want to panic if pp->pp_ref is nonzero or
+	// pp->pp_link is not NULL.
+}
+
+//
+// Decrement the reference count on a page,
+// freeing it if there are no more refs.
+//
+void
+page_decref(struct PageInfo* pp)
+{
+	if (--pp->pp_ref == 0)
+		page_free(pp);
+}
+
+// Given 'pgdir', a pointer to a page directory, pgdir_walk returns
+// a pointer to the page table entry (PTE) for linear address 'va'.
+// This requires walking the two-level page table structure.
+//
+// The relevant page table page might not exist yet.
+// If this is true, and create == false, then pgdir_walk returns NULL.
+// Otherwise, pgdir_walk allocates a new page table page with page_alloc.
+//    - If the allocation fails, pgdir_walk returns NULL.
+//    - Otherwise, the new page's reference count is incremented,
+//	the page is cleared,
+//	and pgdir_walk returns a pointer into the new page table page.
+//
+// Hint 1: you can turn a PageInfo * into the physical address of the
+// page it refers to with page2pa() from kern/pmap.h.
+//
+// Hint 2: the x86 MMU checks permission bits in both the page directory
+// and the page table, so it's safe to leave permissions in the page
+// directory more permissive than strictly necessary.
+//
+// Hint 3: look at inc/mmu.h for useful macros that manipulate page
+// table and page directory entries.
+//
+pte_t *
+pgdir_walk(pde_t *pgdir, const void *va, int create)
+{
+	// Fill this function in
+	return NULL;
+}
+
+//
+// Map [va, va+size) of virtual address space to physical [pa, pa+size)
+// in the page table rooted at pgdir.  Size is a multiple of PGSIZE, and
+// va and pa are both page-aligned.
+// Use permission bits perm|PTE_P for the entries.
+//
+// This function is only intended to set up the ``static'' mappings
+// above UTOP. As such, it should *not* change the pp_ref field on the
+// mapped pages.
+//
+// Hint: the TA solution uses pgdir_walk
+static void
+boot_map_region(pde_t *pgdir, uintptr_t va, size_t size, physaddr_t pa, int perm)
+{
+	// Fill this function in
+}
+
+//
+// Map the physical page 'pp' at virtual address 'va'.
+// The permissions (the low 12 bits) of the page table entry
+// should be set to 'perm|PTE_P'.
+//
+// Requirements
+//   - If there is already a page mapped at 'va', it should be page_remove()d.
+//   - If necessary, on demand, a page table should be allocated and inserted
+//     into 'pgdir'.
+//   - pp->pp_ref should be incremented if the insertion succeeds.
+//   - The TLB must be invalidated if a page was formerly present at 'va'.
+//
+// Corner-case hint: Make sure to consider what happens when the same
+// pp is re-inserted at the same virtual address in the same pgdir.
+// However, try not to distinguish this case in your code, as this
+// frequently leads to subtle bugs; there's an elegant way to handle
+// everything in one code path.
+//
+// RETURNS:
+//   0 on success
+//   -E_NO_MEM, if page table couldn't be allocated
+//
+// Hint: The TA solution is implemented using pgdir_walk, page_remove,
+// and page2pa.
+//
+int
+page_insert(pde_t *pgdir, struct PageInfo *pp, void *va, int perm)
+{
+	// Fill this function in
+	return 0;
+}
+
+//
+// Return the page mapped at virtual address 'va'.
+// If pte_store is not zero, then we store in it the address
+// of the pte for this page.  This is used by page_remove and
+// can be used to verify page permissions for syscall arguments,
+// but should not be used by most callers.
+//
+// Return NULL if there is no page mapped at va.
+//
+// Hint: the TA solution uses pgdir_walk and pa2page.
+//
+struct PageInfo *
+page_lookup(pde_t *pgdir, void *va, pte_t **pte_store)
+{
+	// Fill this function in
+	return NULL;
+}
+
+//
+// Unmaps the physical page at virtual address 'va'.
+// If there is no physical page at that address, silently does nothing.
+//
+// Details:
+//   - The ref count on the physical page should decrement.
+//   - The physical page should be freed if the refcount reaches 0.
+//   - The pg table entry corresponding to 'va' should be set to 0.
+//     (if such a PTE exists)
+//   - The TLB must be invalidated if you remove an entry from
+//     the page table.
+//
+// Hint: The TA solution is implemented using page_lookup,
+// 	tlb_invalidate, and page_decref.
+//
+void
+page_remove(pde_t *pgdir, void *va)
+{
+	// Fill this function in
+}
+
+//
+// Invalidate a TLB entry, but only if the page tables being
+// edited are the ones currently in use by the processor.
+//
+void
+tlb_invalidate(pde_t *pgdir, void *va)
+{
+	// Flush the entry only if we're modifying the current address space.
+	// For now, there is only one address space, so always invalidate.
+	invlpg(va);
+}
+
+
+// --------------------------------------------------------------
+// Checking functions.
+// --------------------------------------------------------------
+
+//
+// Check that the pages on the page_free_list are reasonable.
+//
+static void
+check_page_free_list(bool only_low_memory)
+{
+	struct PageInfo *pp;
+	unsigned pdx_limit = only_low_memory ? 1 : NPDENTRIES;
+	int nfree_basemem = 0, nfree_extmem = 0;
+	char *first_free_page;
+
+	if (!page_free_list)
+		panic("'page_free_list' is a null pointer!");
+
+	if (only_low_memory) {
+		// Move pages with lower addresses first in the free
+		// list, since entry_pgdir does not map all pages.
+		struct PageInfo *pp1, *pp2;
+		struct PageInfo **tp[2] = { &pp1, &pp2 };
+		for (pp = page_free_list; pp; pp = pp->pp_link) {
+			int pagetype = PDX(page2pa(pp)) >= pdx_limit;
+			*tp[pagetype] = pp;
+			tp[pagetype] = &pp->pp_link;
+		}
+		*tp[1] = 0;
+		*tp[0] = pp2;
+		page_free_list = pp1;
+	}
+
+	// if there's a page that shouldn't be on the free list,
+	// try to make sure it eventually causes trouble.
+	for (pp = page_free_list; pp; pp = pp->pp_link)
+		if (PDX(page2pa(pp)) < pdx_limit)
+			memset(page2kva(pp), 0x97, 128);
+
+	first_free_page = (char *) boot_alloc(0);
+	for (pp = page_free_list; pp; pp = pp->pp_link) {
+		// check that we didn't corrupt the free list itself
+		assert(pp >= pages);
+		assert(pp < pages + npages);
+		assert(((char *) pp - (char *) pages) % sizeof(*pp) == 0);
+
+		// check a few pages that shouldn't be on the free list
+		assert(page2pa(pp) != 0);
+		assert(page2pa(pp) != IOPHYSMEM);
+		assert(page2pa(pp) != EXTPHYSMEM - PGSIZE);
+		assert(page2pa(pp) != EXTPHYSMEM);
+		assert(page2pa(pp) < EXTPHYSMEM || (char *) page2kva(pp) >= first_free_page);
+
+		if (page2pa(pp) < EXTPHYSMEM)
+			++nfree_basemem;
+		else
+			++nfree_extmem;
+	}
+
+	assert(nfree_basemem > 0);
+	assert(nfree_extmem > 0);
+
+	cprintf("check_page_free_list() succeeded!\n");
+}
+
+//
+// Check the physical page allocator (page_alloc(), page_free(),
+// and page_init()).
+//
+static void
+check_page_alloc(void)
+{
+	struct PageInfo *pp, *pp0, *pp1, *pp2;
+	int nfree;
+	struct PageInfo *fl;
+	char *c;
+	int i;
+
+	if (!pages)
+		panic("'pages' is a null pointer!");
+
+	// check number of free pages
+	for (pp = page_free_list, nfree = 0; pp; pp = pp->pp_link)
+		++nfree;
+
+	// should be able to allocate three pages
+	pp0 = pp1 = pp2 = 0;
+	assert((pp0 = page_alloc(0)));
+	assert((pp1 = page_alloc(0)));
+	assert((pp2 = page_alloc(0)));
+
+	assert(pp0);
+	assert(pp1 && pp1 != pp0);
+	assert(pp2 && pp2 != pp1 && pp2 != pp0);
+	assert(page2pa(pp0) < npages*PGSIZE);
+	assert(page2pa(pp1) < npages*PGSIZE);
+	assert(page2pa(pp2) < npages*PGSIZE);
+
+	// temporarily steal the rest of the free pages
+	fl = page_free_list;
+	page_free_list = 0;
+
+	// should be no free memory
+	assert(!page_alloc(0));
+
+	// free and re-allocate?
+	page_free(pp0);
+	page_free(pp1);
+	page_free(pp2);
+	pp0 = pp1 = pp2 = 0;
+	assert((pp0 = page_alloc(0)));
+	assert((pp1 = page_alloc(0)));
+	assert((pp2 = page_alloc(0)));
+	assert(pp0);
+	assert(pp1 && pp1 != pp0);
+	assert(pp2 && pp2 != pp1 && pp2 != pp0);
+	assert(!page_alloc(0));
+
+	// test flags
+	memset(page2kva(pp0), 1, PGSIZE);
+	page_free(pp0);
+	assert((pp = page_alloc(ALLOC_ZERO)));
+	assert(pp && pp0 == pp);
+	c = page2kva(pp);
+	for (i = 0; i < PGSIZE; i++)
+		assert(c[i] == 0);
+
+	// give free list back
+	page_free_list = fl;
+
+	// free the pages we took
+	page_free(pp0);
+	page_free(pp1);
+	page_free(pp2);
+
+	// number of free pages should be the same
+	for (pp = page_free_list; pp; pp = pp->pp_link)
+		--nfree;
+	assert(nfree == 0);
+
+	cprintf("check_page_alloc() succeeded!\n");
+}
+
+//
+// Checks that the kernel part of virtual address space
+// has been set up roughly correctly (by mem_init()).
+//
+// This function doesn't test every corner case,
+// but it is a pretty good sanity check.
+//
+
+static void
+check_kern_pgdir(void)
+{
+	uint32_t i, n;
+	pde_t *pgdir;
+
+	pgdir = kern_pgdir;
+
+	// check pages array
+	n = ROUNDUP(npages*sizeof(struct PageInfo), PGSIZE);
+	for (i = 0; i < n; i += PGSIZE)
+		assert(check_va2pa(pgdir, UPAGES + i) == PADDR(pages) + i);
+
+
+	// check phys mem
+	for (i = 0; i < npages * PGSIZE; i += PGSIZE)
+		assert(check_va2pa(pgdir, KERNBASE + i) == i);
+
+	// check kernel stack
+	for (i = 0; i < KSTKSIZE; i += PGSIZE)
+		assert(check_va2pa(pgdir, KSTACKTOP - KSTKSIZE + i) == PADDR(bootstack) + i);
+	assert(check_va2pa(pgdir, KSTACKTOP - PTSIZE) == ~0);
+
+	// check PDE permissions
+	for (i = 0; i < NPDENTRIES; i++) {
+		switch (i) {
+		case PDX(UVPT):
+		case PDX(KSTACKTOP-1):
+		case PDX(UPAGES):
+			assert(pgdir[i] & PTE_P);
+			break;
+		default:
+			if (i >= PDX(KERNBASE)) {
+				assert(pgdir[i] & PTE_P);
+				assert(pgdir[i] & PTE_W);
+			} else
+				assert(pgdir[i] == 0);
+			break;
+		}
+	}
+	cprintf("check_kern_pgdir() succeeded!\n");
+}
+
+// This function returns the physical address of the page containing 'va',
+// defined by the page directory 'pgdir'.  The hardware normally performs
+// this functionality for us!  We define our own version to help check
+// the check_kern_pgdir() function; it shouldn't be used elsewhere.
+
+static physaddr_t
+check_va2pa(pde_t *pgdir, uintptr_t va)
+{
+	pte_t *p;
+
+	pgdir = &pgdir[PDX(va)];
+	if (!(*pgdir & PTE_P))
+		return ~0;
+	p = (pte_t*) KADDR(PTE_ADDR(*pgdir));
+	if (!(p[PTX(va)] & PTE_P))
+		return ~0;
+	return PTE_ADDR(p[PTX(va)]);
+}
+
+
+// check page_insert, page_remove, &c
+static void
+check_page(void)
+{
+	struct PageInfo *pp, *pp0, *pp1, *pp2;
+	struct PageInfo *fl;
+	pte_t *ptep, *ptep1;
+	void *va;
+	int i;
+	extern pde_t entry_pgdir[];
+
+	// should be able to allocate three pages
+	pp0 = pp1 = pp2 = 0;
+	assert((pp0 = page_alloc(0)));
+	assert((pp1 = page_alloc(0)));
+	assert((pp2 = page_alloc(0)));
+
+	assert(pp0);
+	assert(pp1 && pp1 != pp0);
+	assert(pp2 && pp2 != pp1 && pp2 != pp0);
+
+	// temporarily steal the rest of the free pages
+	fl = page_free_list;
+	page_free_list = 0;
+
+	// should be no free memory
+	assert(!page_alloc(0));
+
+	// there is no page allocated at address 0
+	assert(page_lookup(kern_pgdir, (void *) 0x0, &ptep) == NULL);
+
+	// there is no free memory, so we can't allocate a page table
+	assert(page_insert(kern_pgdir, pp1, 0x0, PTE_W) < 0);
+
+	// free pp0 and try again: pp0 should be used for page table
+	page_free(pp0);
+	assert(page_insert(kern_pgdir, pp1, 0x0, PTE_W) == 0);
+	assert(PTE_ADDR(kern_pgdir[0]) == page2pa(pp0));
+	assert(check_va2pa(kern_pgdir, 0x0) == page2pa(pp1));
+	assert(pp1->pp_ref == 1);
+	assert(pp0->pp_ref == 1);
+
+	// should be able to map pp2 at PGSIZE because pp0 is already allocated for page table
+	assert(page_insert(kern_pgdir, pp2, (void*) PGSIZE, PTE_W) == 0);
+	assert(check_va2pa(kern_pgdir, PGSIZE) == page2pa(pp2));
+	assert(pp2->pp_ref == 1);
+
+	// should be no free memory
+	assert(!page_alloc(0));
+
+	// should be able to map pp2 at PGSIZE because it's already there
+	assert(page_insert(kern_pgdir, pp2, (void*) PGSIZE, PTE_W) == 0);
+	assert(check_va2pa(kern_pgdir, PGSIZE) == page2pa(pp2));
+	assert(pp2->pp_ref == 1);
+
+	// pp2 should NOT be on the free list
+	// could happen in ref counts are handled sloppily in page_insert
+	assert(!page_alloc(0));
+
+	// check that pgdir_walk returns a pointer to the pte
+	ptep = (pte_t *) KADDR(PTE_ADDR(kern_pgdir[PDX(PGSIZE)]));
+	assert(pgdir_walk(kern_pgdir, (void*)PGSIZE, 0) == ptep+PTX(PGSIZE));
+
+	// should be able to change permissions too.
+	assert(page_insert(kern_pgdir, pp2, (void*) PGSIZE, PTE_W|PTE_U) == 0);
+	assert(check_va2pa(kern_pgdir, PGSIZE) == page2pa(pp2));
+	assert(pp2->pp_ref == 1);
+	assert(*pgdir_walk(kern_pgdir, (void*) PGSIZE, 0) & PTE_U);
+	assert(kern_pgdir[0] & PTE_U);
+
+	// should be able to remap with fewer permissions
+	assert(page_insert(kern_pgdir, pp2, (void*) PGSIZE, PTE_W) == 0);
+	assert(*pgdir_walk(kern_pgdir, (void*) PGSIZE, 0) & PTE_W);
+	assert(!(*pgdir_walk(kern_pgdir, (void*) PGSIZE, 0) & PTE_U));
+
+	// should not be able to map at PTSIZE because need free page for page table
+	assert(page_insert(kern_pgdir, pp0, (void*) PTSIZE, PTE_W) < 0);
+
+	// insert pp1 at PGSIZE (replacing pp2)
+	assert(page_insert(kern_pgdir, pp1, (void*) PGSIZE, PTE_W) == 0);
+	assert(!(*pgdir_walk(kern_pgdir, (void*) PGSIZE, 0) & PTE_U));
+
+	// should have pp1 at both 0 and PGSIZE, pp2 nowhere, ...
+	assert(check_va2pa(kern_pgdir, 0) == page2pa(pp1));
+	assert(check_va2pa(kern_pgdir, PGSIZE) == page2pa(pp1));
+	// ... and ref counts should reflect this
+	assert(pp1->pp_ref == 2);
+	assert(pp2->pp_ref == 0);
+
+	// pp2 should be returned by page_alloc
+	assert((pp = page_alloc(0)) && pp == pp2);
+
+	// unmapping pp1 at 0 should keep pp1 at PGSIZE
+	page_remove(kern_pgdir, 0x0);
+	assert(check_va2pa(kern_pgdir, 0x0) == ~0);
+	assert(check_va2pa(kern_pgdir, PGSIZE) == page2pa(pp1));
+	assert(pp1->pp_ref == 1);
+	assert(pp2->pp_ref == 0);
+
+	// test re-inserting pp1 at PGSIZE
+	assert(page_insert(kern_pgdir, pp1, (void*) PGSIZE, 0) == 0);
+	assert(pp1->pp_ref);
+	assert(pp1->pp_link == NULL);
+
+	// unmapping pp1 at PGSIZE should free it
+	page_remove(kern_pgdir, (void*) PGSIZE);
+	assert(check_va2pa(kern_pgdir, 0x0) == ~0);
+	assert(check_va2pa(kern_pgdir, PGSIZE) == ~0);
+	assert(pp1->pp_ref == 0);
+	assert(pp2->pp_ref == 0);
+
+	// so it should be returned by page_alloc
+	assert((pp = page_alloc(0)) && pp == pp1);
+
+	// should be no free memory
+	assert(!page_alloc(0));
+
+	// forcibly take pp0 back
+	assert(PTE_ADDR(kern_pgdir[0]) == page2pa(pp0));
+	kern_pgdir[0] = 0;
+	assert(pp0->pp_ref == 1);
+	pp0->pp_ref = 0;
+
+	// check pointer arithmetic in pgdir_walk
+	page_free(pp0);
+	va = (void*)(PGSIZE * NPDENTRIES + PGSIZE);
+	ptep = pgdir_walk(kern_pgdir, va, 1);
+	ptep1 = (pte_t *) KADDR(PTE_ADDR(kern_pgdir[PDX(va)]));
+	assert(ptep == ptep1 + PTX(va));
+	kern_pgdir[PDX(va)] = 0;
+	pp0->pp_ref = 0;
+
+	// check that new page tables get cleared
+	memset(page2kva(pp0), 0xFF, PGSIZE);
+	page_free(pp0);
+	pgdir_walk(kern_pgdir, 0x0, 1);
+	ptep = (pte_t *) page2kva(pp0);
+	for(i=0; i<NPTENTRIES; i++)
+		assert((ptep[i] & PTE_P) == 0);
+	kern_pgdir[0] = 0;
+	pp0->pp_ref = 0;
+
+	// give free list back
+	page_free_list = fl;
+
+	// free the pages we took
+	page_free(pp0);
+	page_free(pp1);
+	page_free(pp2);
+
+	cprintf("check_page() succeeded!\n");
+}
+
+// check page_insert, page_remove, &c, with an installed kern_pgdir
+static void
+check_page_installed_pgdir(void)
+{
+	struct PageInfo *pp, *pp0, *pp1, *pp2;
+	struct PageInfo *fl;
+	pte_t *ptep, *ptep1;
+	uintptr_t va;
+	int i;
+
+	// check that we can read and write installed pages
+	pp1 = pp2 = 0;
+	assert((pp0 = page_alloc(0)));
+	assert((pp1 = page_alloc(0)));
+	assert((pp2 = page_alloc(0)));
+	page_free(pp0);
+	memset(page2kva(pp1), 1, PGSIZE);
+	memset(page2kva(pp2), 2, PGSIZE);
+	page_insert(kern_pgdir, pp1, (void*) PGSIZE, PTE_W);
+	assert(pp1->pp_ref == 1);
+	assert(*(uint32_t *)PGSIZE == 0x01010101U);
+	page_insert(kern_pgdir, pp2, (void*) PGSIZE, PTE_W);
+	assert(*(uint32_t *)PGSIZE == 0x02020202U);
+	assert(pp2->pp_ref == 1);
+	assert(pp1->pp_ref == 0);
+	*(uint32_t *)PGSIZE = 0x03030303U;
+	assert(*(uint32_t *)page2kva(pp2) == 0x03030303U);
+	page_remove(kern_pgdir, (void*) PGSIZE);
+	assert(pp2->pp_ref == 0);
+
+	// forcibly take pp0 back
+	assert(PTE_ADDR(kern_pgdir[0]) == page2pa(pp0));
+	kern_pgdir[0] = 0;
+	assert(pp0->pp_ref == 1);
+	pp0->pp_ref = 0;
+
+	// free the pages we took
+	page_free(pp0);
+
+	cprintf("check_page_installed_pgdir() succeeded!\n");
+}

kern/pmap.h

@@ -0,0 +1,87 @@
+/* See COPYRIGHT for copyright information. */
+
+#ifndef JOS_KERN_PMAP_H
+#define JOS_KERN_PMAP_H
+#ifndef JOS_KERNEL
+# error "This is a JOS kernel header; user programs should not #include it"
+#endif
+
+#include <inc/memlayout.h>
+#include <inc/assert.h>
+
+extern char bootstacktop[], bootstack[];
+
+extern struct PageInfo *pages;
+extern size_t npages;
+
+extern pde_t *kern_pgdir;
+
+
+/* This macro takes a kernel virtual address -- an address that points above
+ * KERNBASE, where the machine's maximum 256MB of physical memory is mapped --
+ * and returns the corresponding physical address.  It panics if you pass it a
+ * non-kernel virtual address.
+ */
+#define PADDR(kva) _paddr(__FILE__, __LINE__, kva)
+
+static inline physaddr_t
+_paddr(const char *file, int line, void *kva)
+{
+	if ((uint32_t)kva < KERNBASE)
+		_panic(file, line, "PADDR called with invalid kva %08lx", kva);
+	return (physaddr_t)kva - KERNBASE;
+}
+
+/* This macro takes a physical address and returns the corresponding kernel
+ * virtual address.  It panics if you pass an invalid physical address. */
+#define KADDR(pa) _kaddr(__FILE__, __LINE__, pa)
+
+static inline void*
+_kaddr(const char *file, int line, physaddr_t pa)
+{
+	if (PGNUM(pa) >= npages)
+		_panic(file, line, "KADDR called with invalid pa %08lx", pa);
+	return (void *)(pa + KERNBASE);
+}
+
+
+enum {
+	// For page_alloc, zero the returned physical page.
+	ALLOC_ZERO = 1<<0,
+};
+
+void	mem_init(void);
+
+void	page_init(void);
+struct PageInfo *page_alloc(int alloc_flags);
+void	page_free(struct PageInfo *pp);
+int	page_insert(pde_t *pgdir, struct PageInfo *pp, void *va, int perm);
+void	page_remove(pde_t *pgdir, void *va);
+struct PageInfo *page_lookup(pde_t *pgdir, void *va, pte_t **pte_store);
+void	page_decref(struct PageInfo *pp);
+
+void	tlb_invalidate(pde_t *pgdir, void *va);
+
+static inline physaddr_t
+page2pa(struct PageInfo *pp)
+{
+	return (pp - pages) << PGSHIFT;
+}
+
+static inline struct PageInfo*
+pa2page(physaddr_t pa)
+{
+	if (PGNUM(pa) >= npages)
+		panic("pa2page called with invalid pa");
+	return &pages[PGNUM(pa)];
+}
+
+static inline void*
+page2kva(struct PageInfo *pp)
+{
+	return KADDR(page2pa(pp));
+}
+
+pte_t *pgdir_walk(pde_t *pgdir, const void *va, int create);
+
+#endif /* !JOS_KERN_PMAP_H */