/* 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>
#include <kern/env.h>

// These variables are set by i386_detect_memory()
static physaddr_t maxpa;	// Maximum physical address
size_t npage;			// Amount of physical memory (in pages)
static size_t basemem;		// Amount of base memory (in bytes)
static size_t extmem;		// Amount of extended memory (in bytes)

// These variables are set in i386_vm_init(
pde_t* boot_pgdir;		// Virtual address of boot time page directory
physaddr_t boot_cr3;		// Physical address of boot time page directory
static char* boot_freemem;	// Pointer to next byte of free mem

struct Page* pages;		// Virtual address of physical page array
static struct Page_list page_free_list;	// Free list of physical pages

//environments array
struct Env *envs;

// Global descriptor table.
//
// The kernel and user segments are identical (except for the DPL).
// To load the SS register, the CPL must equal the DPL.  Thus,
// we must duplicate the segments for the user and the kernel.
//
struct Segdesc gdt[] =
{
	// 0x0 - unused (always faults -- for trapping NULL far pointers)
	SEG_NULL,

	// 0x8 - kernel code segment
	[GD_KT >> 3] = SEG(STA_X | STA_R, 0x0, 0xffffffff, 0),

	// 0x10 - kernel data segment
	[GD_KD >> 3] = SEG(STA_W, 0x0, 0xffffffff, 0),

	// 0x18 - user code segment
	[GD_UT >> 3] = SEG(STA_X | STA_R, 0x0, 0xffffffff, 3),

	// 0x20 - user data segment
	[GD_UD >> 3] = SEG(STA_W, 0x0, 0xffffffff, 3),

	// 0x28 - tss, initialized in idt_init()
	[GD_TSS >> 3] = SEG_NULL
};

struct Pseudodesc gdt_pd = {
	sizeof(gdt) - 1, (unsigned long) gdt
};

static int
nvram_read(int r)
{
	return mc146818_read(r) | (mc146818_read(r + 1) << 8);
}

void
i386_detect_memory(void)
{
	// CMOS tells us how many kilobytes there are
	basemem = ROUNDDOWN(nvram_read(NVRAM_BASELO)*1024, PGSIZE);
	extmem = ROUNDDOWN(nvram_read(NVRAM_EXTLO)*1024, PGSIZE);

	// Calculate the maximum physical address based on whether
	// or not there is any extended memory.  See comment in <inc/mmu.h>.
	if (extmem)
		maxpa = EXTPHYSMEM + extmem;
	else
		maxpa = basemem;

	npage = maxpa / PGSIZE;

	cprintf("Physical memory: %dK available, ", (int)(maxpa/1024));
	cprintf("base = %dK, extended = %dK\n", (int)(basemem/1024), (int)(extmem/1024));
}

// --------------------------------------------------------------
// Set up initial memory mappings and turn on MMU.
// --------------------------------------------------------------

static void check_boot_pgdir(void);
static void check_page_alloc();
static void page_check(void);
static void boot_map_segment(pde_t *pgdir, uintptr_t la, size_t size, physaddr_t pa, int perm);
static void boot_map_big_segment(pde_t *pgdir, uintptr_t la, size_t size, physaddr_t pa, int perm);

//
// A simple physical memory allocator, used only a few times
// in the process of setting up the virtual memory system.
// page_alloc() is the real allocator.
//
// Allocate n bytes of physical memory aligned on an 
// align-byte boundary.  Align must be a power of two.
// Return kernel virtual address.  Returned memory is uninitialized.
//
// If we're out of memory, boot_alloc should panic.
// This function may ONLY be used during initialization,
// before the page_free_list has been set up.
// 
static void*
boot_alloc(uint32_t n, uint32_t align)
{
	extern char end[];
	void *v;

	// Initialize boot_freemem 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 -
	// i.e., the first virtual address that the linker
	// did _not_ assign to any kernel code or global variables.
	if (boot_freemem == 0)
		boot_freemem = end;

	//	Step 1: round boot_freemem up to be aligned properly
	boot_freemem = ROUNDUP(boot_freemem, align);
	//cprintf("boot_freemem rounded: %08x\n",boot_freemem);
	//	Step 2: save current value of boot_freemem as allocated chunk
	v = boot_freemem;
	//	Step 3: increase boot_freemem to record allocation
	boot_freemem = boot_freemem + n;
	//	Step 4: return allocated chunk
	return v;
}

static physaddr_t check_va2pa(pde_t *pgdir, uintptr_t va);

// Set up a two-level page table:
//    boot_pgdir is its linear (virtual) address of the root
//    boot_cr3 is the physical adresss of the root
// Then turn on paging.  Then effectively turn off segmentation.
// (i.e., the segment base addrs are set to zero).
// 
// This function only sets up the kernel part of the address space
// (ie. addresses >= UTOP).  The user part of the address space
// will be setup later.
//
// From UTOP to ULIM, the user is allowed to read but not write.
// Above ULIM the user cannot read (or write). 
void
i386_vm_init(void)
{
	pde_t* pgdir;
	uint32_t cr0, cr4;
	size_t n;

	//////////////////////////////////////////////////////////////////////
	// create initial page directory.
	pgdir = boot_alloc(PGSIZE, PGSIZE);
	memset(pgdir, 0, PGSIZE);
	boot_pgdir = pgdir;
	boot_cr3 = PADDR(pgdir);

	//////////////////////////////////////////////////////////////////////
	// Recursively insert PD in itself as a page table, to form
	// a virtual page table at virtual address VPT.
	// (For now, you don't have understand the greater purpose of the
	// following two lines.)

	// Permissions: kernel RW, user NONE
	pgdir[PDX(VPT)] = PADDR(pgdir)|PTE_W|PTE_P;

	// same for UVPT
	// Permissions: kernel R, user R 
	pgdir[PDX(UVPT)] = PADDR(pgdir)|PTE_U|PTE_P;

	//////////////////////////////////////////////////////////////////////
	// Make 'pages' point to an array of size 'npage' of 'struct Page'.
	// The kernel uses this structure to keep track of physical pages;
	// 'npage' equals the number of physical pages in memory.  User-level
	// programs will get read-only access to the array as well.
	// You must allocate the array yourself.
	// Your code goes here: 
	pages = boot_alloc(npage * sizeof(struct Page),PGSIZE);

	//////////////////////////////////////////////////////////////////////
	// Make 'envs' point to an array of size 'NENV' of 'struct Env'.
	// LAB 3: Your code here.
	envs = boot_alloc(NENV * sizeof(struct Env), PGSIZE);

	//////////////////////////////////////////////////////////////////////
	// 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_segment or page_insert
	page_init();

        check_page_alloc();

	page_check();

	//////////////////////////////////////////////////////////////////////
	// Now we set up virtual memory 
	
	//////////////////////////////////////////////////////////////////////
	// Map 'pages' read-only by the user at linear address UPAGES
	// (ie. perm = PTE_U | PTE_P)
	// Permissions:
	//    - pages -- kernel RW, user NONE
	//    - the read-only version mapped at UPAGES -- kernel R, user R
	// Your code goes here:
	size_t total_size = ROUNDUP(npage*sizeof(struct Page), PGSIZE);
	//cprintf("virtual user pages address: %08x\n",UPAGES);
	//cprintf("physical user pages address: %08x\n",PADDR(pages));
	boot_map_segment(pgdir, (uintptr_t)UPAGES, total_size, PADDR(pages), PTE_U);
	boot_map_segment(pgdir, (uintptr_t)pages, total_size, PADDR(pages), PTE_W);

	//////////////////////////////////////////////////////////////////////
	// Map the 'envs' array read-only by the user at linear address UENVS
	// (ie. perm = PTE_U | PTE_P).
	// Permissions:
	//    - envs itself -- kernel RW, user NONE
	//    - the image of envs mapped at UENVS  -- kernel R, user R
	total_size = ROUNDUP(NENV*sizeof(struct Env), PGSIZE);
	boot_map_segment(pgdir, (uintptr_t)UENVS, total_size, PADDR(envs), PTE_U);
	boot_map_segment(pgdir, (uintptr_t)envs, total_size, PADDR(envs), PTE_W);

	//////////////////////////////////////////////////////////////////////
	// Map the kernel stack (symbol name "bootstack").  The complete VA
	// range of the stack, [KSTACKTOP-PTSIZE, KSTACKTOP), breaks into two
	// pieces:
	//     * [KSTACKTOP-KSTKSIZE, KSTACKTOP) -- backed by physical memory
	//     * [KSTACKTOP-PTSIZE, KSTACKTOP-KSTKSIZE) -- not backed => faults
	//     Permissions: kernel RW, user NONE
	// Your code goes here:
	boot_map_segment(pgdir, (uintptr_t)(KSTACKTOP-KSTKSIZE), (size_t)KSTKSIZE, 
					 PADDR(&bootstack), (PTE_W|PTE_P));
	//cprintf("test value: pgdir_walk = %08x\n",*(pgdir_walk(pgdir,(void*)UPAGES,0))); 
	//cprintf("test value: check_va2pa = %08x\n",check_va2pa(pgdir,UPAGES));
	boot_map_segment(pgdir, (uintptr_t)(KSTACKTOP-PTSIZE), (size_t)(PTSIZE-KSTKSIZE), 
					 PADDR(&bootstack), (PTE_W|PTE_P));

	//////////////////////////////////////////////////////////////////////
	// 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 amapping anyway.
	// Permissions: kernel RW, user NONE
	// Your code goes here: 
	total_size = ROUNDDOWN(0xFFFFFFFF-KERNBASE, BIGPGSIZE);
	//boot_map_segment(pgdir, (uintptr_t)KERNBASE, total_size, (physaddr_t)0, (PTE_W|PTE_P));	 
	boot_map_big_segment(pgdir, (uintptr_t)KERNBASE, total_size, (physaddr_t)0, (PTE_W|PTE_P));  

	// Check that the initial page directory has been set up correctly.
	check_boot_pgdir();

	//////////////////////////////////////////////////////////////////////
	// On x86, segmentation maps a VA to a LA (linear addr) and
	// paging maps the LA to a PA.  I.e. VA => LA => PA.  If paging is
	// turned off the LA is used as the PA.  Note: there is no way to
	// turn off segmentation.  The closest thing is to set the base
	// address to 0, so the VA => LA mapping is the identity.

	// Current mapping: VA KERNBASE+x => PA x.
	//     (segmentation base=-KERNBASE and paging is off)

	// From here on down we must maintain this VA KERNBASE + x => PA x
	// mapping, even though we are turning on paging and reconfiguring
	// segmentation.

	// Map VA 0:4MB same as VA KERNBASE, i.e. to PA 0:4MB.
	// (Limits our kernel to <4MB)
	pgdir[0] = pgdir[PDX(KERNBASE)];

	// Install page table.
	lcr3(boot_cr3);

	//turn on page size extension
	cr4 = rcr4();
	cr4 |= CR4_PSE;
	lcr4(cr4);

	// Turn on paging.
	cr0 = rcr0();
	cr0 |= CR0_PE|CR0_PG|CR0_AM|CR0_WP|CR0_NE|CR0_TS|CR0_EM|CR0_MP;
	cr0 &= ~(CR0_TS|CR0_EM);
	lcr0(cr0);

	// Current mapping: KERNBASE+x => x => x.
	// (x < 4MB so uses paging pgdir[0])

	// Reload all segment registers.
	asm volatile("lgdt gdt_pd");
	asm volatile("movw %%ax,%%gs" :: "a" (GD_UD|3));
	asm volatile("movw %%ax,%%fs" :: "a" (GD_UD|3));
	asm volatile("movw %%ax,%%es" :: "a" (GD_KD));
	asm volatile("movw %%ax,%%ds" :: "a" (GD_KD));
	asm volatile("movw %%ax,%%ss" :: "a" (GD_KD));
	asm volatile("ljmp %0,$1f\n 1:\n" :: "i" (GD_KT));  // reload cs
	asm volatile("lldt %%ax" :: "a" (0));

	// Final mapping: KERNBASE+x => KERNBASE+x => x.

	// This mapping was only used after paging was turned on but
	// before the segment registers were reloaded.
	pgdir[0] = 0;

	// Flush the TLB for good measure, to kill the pgdir[0] mapping.
	lcr3(boot_cr3);
}

//
// Check the physical page allocator (page_alloc(), page_free(),
// and page_init()).
//
static void
check_page_alloc()
{
	struct Page *pp, *pp0, *pp1, *pp2;
	struct Page_list fl;
	
        // if there's a page that shouldn't be on
        // the free list, try to make sure it
        // eventually causes trouble.
	LIST_FOREACH(pp0, &page_free_list, pp_link)
		memset(page2kva(pp0), 0x97, 128);

	// should be able to allocate three pages
	pp0 = pp1 = pp2 = 0;
	assert(page_alloc(&pp0) == 0);
	assert(page_alloc(&pp1) == 0);
	assert(page_alloc(&pp2) == 0);

	assert(pp0);
	assert(pp1 && pp1 != pp0);
	assert(pp2 && pp2 != pp1 && pp2 != pp0);
        assert(page2pa(pp0) < npage*PGSIZE);
        assert(page2pa(pp1) < npage*PGSIZE);
        assert(page2pa(pp2) < npage*PGSIZE);

	// temporarily steal the rest of the free pages
	fl = page_free_list;
	LIST_INIT(&page_free_list);

	// should be no free memory
	assert(page_alloc(&pp) == -E_NO_MEM);

        // free and re-allocate?
        page_free(pp0);
        page_free(pp1);
        page_free(pp2);
	pp0 = pp1 = pp2 = 0;
	assert(page_alloc(&pp0) == 0);
	assert(page_alloc(&pp1) == 0);
	assert(page_alloc(&pp2) == 0);
	assert(pp0);
	assert(pp1 && pp1 != pp0);
	assert(pp2 && pp2 != pp1 && pp2 != pp0);
	assert(page_alloc(&pp) == -E_NO_MEM);

	// 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_alloc() succeeded!\n");
}

//
// Checks that the kernel part of virtual address space
// has been setup roughly correctly(by i386_vm_init()).
//
// This function doesn't test every corner case,
// in fact it doesn't test the permission bits at all,
// but it is a pretty good sanity check. 
//
static physaddr_t check_va2pa(pde_t *pgdir, uintptr_t va);

static void
check_boot_pgdir(void)
{
	uint32_t i, n;
	pde_t *pgdir;

	pgdir = boot_pgdir;

	// check pages array
	n = ROUNDUP(npage*sizeof(struct Page), PGSIZE);
	for (i = 0; i < n; i += PGSIZE)
		assert(check_va2pa(pgdir, UPAGES + i) == PADDR(pages) + i);
	
	// check envs array (new test for lab 3)
	n = ROUNDUP(NENV*sizeof(struct Env), PGSIZE);
	for (i = 0; i < n; i += PGSIZE)
		assert(check_va2pa(pgdir, UENVS + i) == PADDR(envs) + i);

	// check phys mem
	for (i = 0; i < npage; 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);

	// check for zero/non-zero in PDEs
	for (i = 0; i < NPDENTRIES; i++) {
		switch (i) {
		case PDX(VPT):
		case PDX(UVPT):
		case PDX(KSTACKTOP-1):
		case PDX(UPAGES):
		case PDX(UENVS):
			assert(pgdir[i]);
			break;
		default:
			if (i >= PDX(KERNBASE))
				assert(pgdir[i]);
			else
				assert(pgdir[i] == 0);
			break;
		}
	}
	cprintf("check_boot_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_boot_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;
	}
	//cprintf("check_va2pa: va = %08x\n",va);	   
	if(*pgdir & PTE_PS){
		return PTE_ADDR(*pgdir) + (va&0x003FFFF) ;
	}
	p = (pte_t*) KADDR(PTE_ADDR(*pgdir));
	//cprintf("check_va2pa: not valid page 2 %08x\n",p);
	//cprintf("check_va2pa: entry = %08x\n",p[PTX(va)]); 
	if (!(p[PTX(va)] & PTE_P)){
		return ~0;
	}
	return PTE_ADDR(p[PTX(va)]);
}
		
// --------------------------------------------------------------
// Tracking of physical pages.
// The 'pages' array has one 'struct Page' 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 point, ONLY use the functions below
// to allocate and deallocate physical memory via the page_free_list,
// and NEVER use boot_alloc()
//
void
page_init(void)
{
	// The example code here marks all pages as free.
	// However this is not truly the case.  What memory is free?
	//  1) Mark 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) Mark the rest of base memory as free.
	//  3) Then comes the IO hole [IOPHYSMEM, EXTPHYSMEM).
	//     Mark it as in use so that it can never be allocated.      
	//  4) Then extended memory [EXTPHYSMEM, ...).
	//     Some of it is in use, some is free. Where is the kernel?
	//     Which pages are used for page tables and other data structures?
	//
	// Change the code to reflect this.
	int i;
	LIST_INIT(&page_free_list);
	
	pages[0].pp_ref = 1;
	//low memory
	for (i = 1; i < IOPHYSMEM/PGSIZE; i++) {
		pages[i].pp_ref = 0;
		LIST_INSERT_HEAD(&page_free_list, &pages[i], pp_link);
	}
	//I/O hole
	for (; i < EXTPHYSMEM/PGSIZE; i++){
		pages[i].pp_ref = 1;
	}
	//kernel code and data
	for(; i < ((uint32_t) PADDR(boot_freemem))/PGSIZE; i++) {
		pages[i].pp_ref = 1;
	}
	for(; i < npage; i++){
		pages[i].pp_ref = 0;
		//cprintf("extended memory page %08x\n", &pages[i]);
		LIST_INSERT_HEAD(&page_free_list, &pages[i], pp_link);
	}
}

//
// Initialize a Page structure.
// The result has null links and 0 refcount.
// Note that the corresponding physical page is NOT initialized!
//
static void
page_initpp(struct Page *pp)
{
	memset(pp, 0, sizeof(*pp));
}

//
// Allocates a physical page.
// Does NOT set the contents of the physical page to zero -
// the caller must do that if necessary.
//
// *pp_store -- is set to point to the Page struct of the newly allocated
// page
//
// RETURNS 
//   0 -- on success
//   -E_NO_MEM -- otherwise 
//
// Hint: use LIST_FIRST, LIST_REMOVE, and page_initpp
// Hint: pp_ref should not be incremented 
int
page_alloc(struct Page **pp_store)
{
	if (LIST_EMPTY(&page_free_list)){
	return -E_NO_MEM;
	} else {
		//cprintf("page alloc: page_alloc start %08x\n",pp_store);
		struct Page *p = LIST_FIRST(&page_free_list);
		LIST_REMOVE(p,pp_link);
		//cprintf("page alloc: take it out of the list\n");
		page_initpp(p);
		//cprintf("page alloc: initialize page\n");
		*pp_store = p;
		//cprintf("page alloc: *pp_store = %08x\n",pp_store);
		//cprintf("page alloc: p = %08x\n",p);
		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 Page *pp)
{
	LIST_INSERT_HEAD(&page_free_list,pp,pp_link);
}

//
// Decrement the reference count on a page,
// freeing it if there are no more refs.
//
void
page_decref(struct Page* 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.
//
// If the relevant page table doesn't exist in the page directory, then:
//    - If create == 0, pgdir_walk returns NULL.
//    - Otherwise, pgdir_walk tries to allocate a new page table
//	with page_alloc.  If this fails, pgdir_walk returns NULL.
//    - pgdir_walk sets pp_ref to 1 for the new page table.
//    - Finally, pgdir_walk returns a pointer into the new page table.
//
// Hint: you can turn a Page * into the physical address of the
// page it refers to with page2pa() from kern/pmap.h.
pte_t *
pgdir_walk(pde_t *pgdir, const void *va, int create)
{
	pde_t *ent;
	ent = pgdir + PDX(va);
	//cprintf("pgdir walk: page entry table address: %08x\n", ent);
	//cprintf("pgdir walk: page entry table entry: %08x\n",*ent);
	pte_t *ret;
  
	if ((*ent&PTE_P) == 0){
		//not present
		//cprintf("pgdir walk: page entry not present\n");
		if (create == 0){
			ret = NULL;
		} else {
			struct Page *p = 0;
			struct Page **new_page = &p;
			//cprintf("pgdir walk: allocate new page\n");
			if (page_alloc(new_page) == 0){
				//cprintf("pgdir walk: got new page: %08x\n",p);
				++(p)->pp_ref;
				physaddr_t page_addr = page2pa(p);
				memset(KADDR(page_addr),0,PGSIZE);
				*ent = PTE_ADDR(page_addr)|PTE_W|PTE_U|PTE_P;
				ret = ((pte_t*) KADDR(page_addr)) + PTX(va);
				//cprintf("page_addr = %08x\n",page_addr);
				//cprintf("ret = %08x\n",ret);
				//cprintf("*ent = %08x\n",*ent);
				//cprintf("pp_ref = %d\n",p->pp_ref);
			} else {
				//cprintf("pgdir walk: couldn't find page\n");
				ret = NULL;
			}
		}
	} else {
		ret = ((pte_t*) KADDR(PTE_ADDR(*ent))) + PTX(va);
	}
	return ret;									 
}

//
// 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'.
//
// Details
//   - If there is already a page mapped at 'va', it is page_remove()d.
//   - If necessary, on demand, allocates a page table and inserts it 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'.
//
// 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 Page *pp, void *va, int perm) 
{
	//retrieve page table entry, creating new tables if necessary
	pte_t *ent;
	ent = pgdir_walk(pgdir,va,1);
	//cprintf("page insert: finished adding page tables: %08x\n",ent);
	//cprintf("page insert: value: %08x\n",*ent);
	int ret;
	if (ent == NULL){
		ret = -E_NO_MEM;
	} else {
		//cprintf("page insert: page table entry pointer %08x\n",ent);
		//cprintf("page insert: page table entry %08x\n",*ent);
		physaddr_t page_addr = page2pa(pp);
		++pp->pp_ref;
		if ((*ent&PTE_P) != 0){
			//cprintf("page insert: page already exists at %08x\n",*ent);
			//already a page there, so the page needs to be removed
			page_remove(pgdir,va);
			tlb_invalidate(pgdir,va);
		}
		*ent = page_addr | perm | PTE_P;
		//cprintf("page insert: page table entry %08x\n",*ent);
		ret = 0;
	}
	return ret;
}

//
// Map [la, la+size) of linear address space to physical [pa, pa+size)
// in the page table rooted at pgdir.  Size is a multiple of PGSIZE.
// 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_segment(pde_t *pgdir, uintptr_t la, size_t size, physaddr_t pa, int perm)
{
	uint32_t i;
	pte_t *ent;
	//for each page
	for (i = 0; i < size; i+=PGSIZE){
		ent = pgdir_walk(pgdir, (void*)la+i, 1);
		*ent = (pa+i) | perm | PTE_P;	 
		//	  if(i==0){
		//	cprintf("boot_map_segment: la = %08x\n",la);
		//	cprintf("boot_map_segment: *ent = %08x\n",*ent);
		//}
	}
}

//used to map big pages using PTE_PS, therefore size is a multiple of BIGPGSIZE
static void
boot_map_big_segment(pde_t *pgdir, uintptr_t la, size_t size, physaddr_t pa, int perm)
{
	uint32_t i;
	pte_t *ent;
	pte_t *base = pgdir + PDX(la); 
	//for each page
	for (i = 0; i <= (size/BIGPGSIZE); i++){
		ent = base + i;
		*ent = (pa+i*BIGPGSIZE) | perm | PTE_P | PTE_PS;	
		//if(i==0){
		//	cprintf("boot_map_big_segment: la = %08x\n",la);
		//	cprintf("boot_map_big_segment: *ent = %08x\n",*ent);
		//}
	}
	//cprintf("boot_map_big_segment: total pages mapped = %d\n",i);
}

//
// 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
// but should not be used by other callers.
//
// Return 0 if there is no page mapped at va.
//
// Hint: the TA solution uses pgdir_walk and pa2page.
//
struct Page *
page_lookup(pde_t *pgdir, void *va, pte_t **pte_store)
{
	pte_t *ent = pgdir_walk(pgdir,va,0);
	if ((ent == NULL) || (((*ent)& PTE_P) == 0)) {
		return 0;
	} else {
		if(pte_store != 0){
			*pte_store = ent;
		}
		return pa2page(PTE_ADDR(*ent));
	}
}

//
// 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 pg dir/pg table.
//
// Hint: The TA solution is implemented using page_lookup,
// 	tlb_invalidate, and page_decref.
//
void
page_remove(pde_t *pgdir, void *va)
{
	struct Page *p;
	pte_t *pte = 0;
	p = page_lookup(pgdir,va,&pte);
	//cprintf("page remove: page address %08x\n",p);
	if (p != 0){
		//if the page exists
		memset(pte,0,4);
		page_decref(p);
		tlb_invalidate(pgdir,va);
	}
}

//
// 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.
	if (!curenv || curenv->env_pgdir == pgdir)
		invlpg(va);
}

static uintptr_t user_mem_check_addr;

//
// Check that an environment is allowed to access the range of memory
// [va, va+len) with permissions 'perm | PTE_P'.
// Normally 'perm' will contain PTE_U at least, but this is not required.
// 'va' and 'len' need not be page-aligned; you must test every page that
// contains any of that range.  You will test either 'len/PGSIZE',
// 'len/PGSIZE + 1', or 'len/PGSIZE + 2' pages.
//
// A user program can access a virtual address if (1) the address is below
// ULIM, and (2) the page table gives it permission.  These are exactly
// the tests you should implement here.
//
// If there is an error, set the 'user_mem_check_addr' variable to the first
// erroneous virtual address.
//
// Returns 0 if the user program can access this range of addresses,
// and -E_FAULT otherwise.
//
int
user_mem_check(struct Env *env, const void *va, size_t len, int perm)
{
	// LAB 3: Your code here. 
	void *va_r = (void *) ROUNDDOWN(va,PGSIZE);
	size_t len_r = ROUNDUP(len,PGSIZE);
    //cprintf("checking %08x to %d\n",va_r,len_r);
	int i;
	pde_t pde;
	pte_t *pte_p;
	for(i = 0; i < len_r; i+=PGSIZE) {
		pde = env->env_pgdir[PDX(va_r+i)];
		pte_p = pgdir_walk(env->env_pgdir, va_r+i, 0);
		if ((pte_p == NULL) || (((uintptr_t)(va_r+i)) > ULIM) || 
			((*pte_p & pde & (perm|PTE_P)) != (perm|PTE_P))) {
			user_mem_check_addr = (uintptr_t) (va+i);
			return -E_FAULT;
		}
	}
	return 0;
}

//
// Checks that environment 'env' is allowed to access the range
// of memory [va, va+len) with permissions 'perm | PTE_U'.
// If it can, then the function simply returns.
// If it cannot, 'env' is destroyed.
//
void
user_mem_assert(struct Env *env, const void *va, size_t len, int perm)
{
	if (user_mem_check(env, va, len, perm | PTE_U) < 0) {
		cprintf("[%08x] user_mem_check assertion failure for "
			"va %08x\n", curenv->env_id, user_mem_check_addr);
		env_destroy(env);	// may not return
	}
}

// check page_insert, page_remove, &c
static void
page_check(void)
{
	struct Page *pp, *pp0, *pp1, *pp2;
	struct Page_list fl;
	pte_t *ptep, *ptep1;
	void *va;
	int i;

	// should be able to allocate three pages
	pp0 = pp1 = pp2 = 0;
	assert(page_alloc(&pp0) == 0);
	assert(page_alloc(&pp1) == 0);
	assert(page_alloc(&pp2) == 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;
	LIST_INIT(&page_free_list);

	// should be no free memory
	assert(page_alloc(&pp) == -E_NO_MEM);

	// there is no page allocated at address 0
	assert(page_lookup(boot_pgdir, (void *) 0x0, &ptep) == NULL);

	// there is no free memory, so we can't allocate a page table 
	assert(page_insert(boot_pgdir, pp1, 0x0, 0) < 0);

	// free pp0 and try again: pp0 should be used for page table
	page_free(pp0);
	assert(page_insert(boot_pgdir, pp1, 0x0, 0) == 0);
	assert(PTE_ADDR(boot_pgdir[0]) == page2pa(pp0));
	assert(check_va2pa(boot_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(boot_pgdir, pp2, (void*) PGSIZE, 0) == 0);
	assert(check_va2pa(boot_pgdir, PGSIZE) == page2pa(pp2));
	assert(pp2->pp_ref == 1);

	// should be no free memory
	assert(page_alloc(&pp) == -E_NO_MEM);

	// should be able to map pp2 at PGSIZE because it's already there
	assert(page_insert(boot_pgdir, pp2, (void*) PGSIZE, 0) == 0);
	assert(check_va2pa(boot_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(&pp) == -E_NO_MEM);

	// check that pgdir_walk returns a pointer to the pte
	ptep = KADDR(PTE_ADDR(boot_pgdir[PDX(PGSIZE)]));
	assert(pgdir_walk(boot_pgdir, (void*)PGSIZE, 0) == ptep+PTX(PGSIZE));

	// should be able to change permissions too.
	assert(page_insert(boot_pgdir, pp2, (void*) PGSIZE, PTE_U) == 0);
	assert(check_va2pa(boot_pgdir, PGSIZE) == page2pa(pp2));
	assert(pp2->pp_ref == 1);
	assert(*pgdir_walk(boot_pgdir, (void*) PGSIZE, 0) & PTE_U);
	
	// should not be able to map at PTSIZE because need free page for page table
	assert(page_insert(boot_pgdir, pp0, (void*) PTSIZE, 0) < 0);

	// insert pp1 at PGSIZE (replacing pp2)
	assert(page_insert(boot_pgdir, pp1, (void*) PGSIZE, 0) == 0);

	// should have pp1 at both 0 and PGSIZE, pp2 nowhere, ...
	assert(check_va2pa(boot_pgdir, 0) == page2pa(pp1));
	assert(check_va2pa(boot_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(page_alloc(&pp) == 0 && pp == pp2);

	// unmapping pp1 at 0 should keep pp1 at PGSIZE
	page_remove(boot_pgdir, 0x0);
	assert(check_va2pa(boot_pgdir, 0x0) == ~0);
	assert(check_va2pa(boot_pgdir, PGSIZE) == page2pa(pp1));
	assert(pp1->pp_ref == 1);
	assert(pp2->pp_ref == 0);

	// unmapping pp1 at PGSIZE should free it
	page_remove(boot_pgdir, (void*) PGSIZE);
	assert(check_va2pa(boot_pgdir, 0x0) == ~0);
	assert(check_va2pa(boot_pgdir, PGSIZE) == ~0);
	assert(pp1->pp_ref == 0);
	assert(pp2->pp_ref == 0);

	// so it should be returned by page_alloc
	assert(page_alloc(&pp) == 0 && pp == pp1);

	// should be no free memory
	assert(page_alloc(&pp) == -E_NO_MEM);
	
#if 0
	// should be able to page_insert to change a page
	// and see the new data immediately.
	memset(page2kva(pp1), 1, PGSIZE);
	memset(page2kva(pp2), 2, PGSIZE);
	page_insert(boot_pgdir, pp1, 0x0, 0);
	assert(pp1->pp_ref == 1);
	assert(*(int*)0 == 0x01010101);
	page_insert(boot_pgdir, pp2, 0x0, 0);
	assert(*(int*)0 == 0x02020202);
	assert(pp2->pp_ref == 1);
	assert(pp1->pp_ref == 0);
	page_remove(boot_pgdir, 0x0);
	assert(pp2->pp_ref == 0);
#endif

	// forcibly take pp0 back
	assert(PTE_ADDR(boot_pgdir[0]) == page2pa(pp0));
	boot_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(boot_pgdir, va, 1);
	ptep1 = KADDR(PTE_ADDR(boot_pgdir[PDX(va)]));
	assert(ptep == ptep1 + PTX(va));
	boot_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(boot_pgdir, 0x0, 1);
	ptep = page2kva(pp0);
	for(i=0; i<NPTENTRIES; i++)
		assert((ptep[i] & PTE_P) == 0);
	boot_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("page_check() succeeded!\n");
}