/*
* Locate the physical frame number for the given vaddr using the page table.
*
* If the entry is invalid and not on swap, then this is the first reference
* to the page and a (simulated) physical frame should be allocated and
* initialized (using init_frame).
*
* If the entry is invalid and on swap, then a (simulated) physical frame
* should be allocated and filled by reading the page data from swap.
*
* Counters for hit, miss and reference events should be incremented in
* this function.
*/
char *find_physpage(addr_t vaddr, char type) {
pgtbl_entry_t *p=NULL; // pointer to the full page table entry for vaddr
unsigned idx = PGDIR_INDEX(vaddr); // get index into page directory
// IMPLEMENTATION NEEDED
// Use top-level page directory to get pointer to 2nd-level page table
if (!(pgdir[idx].pde & PG_VALID)){
pgdir[idx] = init_second_level();
}
// Use vaddr to get index into 2nd-level page table and initialize 'p'
uintptr_t ptr_table = PAGE_MASK & pgdir[idx].pde;
p = (pgtbl_entry_t*)(ptr_table) + PGTBL_INDEX(vaddr);
// Check if p is valid or not, on swap or not, and handle appropriately
// Page is present in the memory
if (p->frame & PG_VALID){
hit_count++;
// Page is not present in the memory
} else {
miss_count++;
ref_count++;
int frame = allocate_frame(p);
// Page on disk.
if (p->frame & PG_ONSWAP){
swap_pagein(frame, p->swap_off);
p->frame = frame << PAGE_SHIFT;
p->frame = p->frame | PG_VALID;
// Page not on disk, first time access the page
} else {
init_frame(frame, vaddr);
p->frame = frame << PAGE_SHIFT;
p->frame = p->frame | PG_DIRTY;
}
}
// Make sure that p is marked valid. Also mark it dirty
// if the access type indicates that the page will be written to
p->frame = p->frame | PG_VALID;
if(type == 'S' || type == 'M'){
p->frame = p->frame | PG_DIRTY;
}
// Call replacement algorithm's ref_fcn for this page
ref_fcn(p);
// p is marked referenced.
p->frame = p->frame | PG_REF;
// Return pointer into (simulated) physical memory at start of frame
return &physmem[(p->frame >> PAGE_SHIFT)*SIMPAGESIZE];
}
/*
* lpage_fault - handle a fault on a specific lpage. If the page is
* not resident, get a physical page from coremap and swap it in.
*
* You do not yet need to distinguish a readonly fault from a write
* fault. When we implement sharing, there will be a difference.
*
* Synchronization: Lock the lpage while checking if it's in memory.
* If it's not, unlock the page while allocting space and loading the
* page in. This only works because lpages are not currently sharable.
* The page should be locked again as soon as it is loaded, but be
* careful of interactions with other locks while modifying the coremap.
*
* After it has been loaded, the page must be pinned so that it is not
* evicted while changes are made to the TLB. It can be unpinned as soon
* as the TLB is updated.
*/
int
lpage_fault(struct lpage *lp, struct addrspace *as, int faulttype, vaddr_t va)
{
paddr_t pa = lp->lp_paddr & PAGE_FRAME;
off_t swap = lp->lp_swapaddr;
int writable = 0;
//lock the page
lpage_lock_and_pin(lp);
//If the page is not in RAM, load into RAM
if(pa == INVALID_PADDR) {
//unlock the page if its not
lpage_unlock(lp);
//allocate a page and pin it
pa = coremap_allocuser(lp);
if(pa == INVALID_PADDR) {
coremap_unpin(lp->lp_paddr & PAGE_FRAME);
return ENOMEM;
}
//assert the page is pinned and lock
KASSERT(coremap_pageispinned(pa));
lock_acquire(global_paging_lock);
//fetch from disk and put in RAM
swap_pagein(pa, swap);
//release locks
lpage_lock(lp);
lock_release(global_paging_lock);
//make sure nobody else paged in the page
KASSERT((lp->lp_paddr & PAGE_FRAME) == INVALID_PADDR);
//set the pages new phyiscal address
lp->lp_paddr = pa;
}
if(faulttype == VM_FAULT_WRITE || faulttype == VM_FAULT_READONLY) {
LP_SET(lp, LPF_DIRTY);
writable = 1;
}
//put a mapping into the TLB
/*if(coremap_pageispinned(lp->lp_paddr) == 0) {
DEBUG(DB_VM, "Page is unpinned!");
}*/
mmu_map(as, va, pa, writable);
lpage_unlock(lp);
return 0;
}
/*
* lpage_fault - handle a fault on a specific lpage. If the page is
* not resident, get a physical page from coremap and swap it in.
*
* You do not yet need to distinguish a readonly fault from a write
* fault. When we implement sharing, there will be a difference.
*
* Synchronization: Lock the lpage while checking if it's in memory.
* If it's not, unlock the page while allocting space and loading the
* page in. This only works because lpages are not currently sharable.
* The page should be locked again as soon as it is loaded, but be
* careful of interactions with other locks while modifying the coremap.
*
* After it has been loaded, the page must be pinned so that it is not
* evicted while changes are made to the TLB. It can be unpinned as soon
* as the TLB is updated.
*/
int
lpage_fault(struct lpage *lp, struct addrspace *as, int faulttype, vaddr_t va)
{
paddr_t pa, swa;
/* Pin the physical page and lock the lpage. */
lpage_lock_and_pin(lp);
// Get the physical address
pa = lp->lp_paddr & PAGE_FRAME;
// If the page is not in memeory, get it from swap
if (pa == INVALID_PADDR) {
swa = lp->lp_swapaddr;
lpage_unlock(lp);
// Have a page frame allocated
pa = coremap_allocuser(lp);
if (pa == INVALID_PADDR) {
coremap_unpin(lp->lp_paddr & PAGE_FRAME);
lpage_destroy(lp);
return ENOMEM;
}
KASSERT(coremap_pageispinned(pa));
lock_acquire(global_paging_lock);
// Add page contents from swap to physical memory
swap_pagein(pa, swa);
lpage_lock(lp);
lock_release(global_paging_lock);
/* Assert nobody else did the pagein. */
KASSERT((lp->lp_paddr & PAGE_FRAME) == INVALID_PADDR);
lp->lp_paddr = pa;
}
//Update TLB
switch (faulttype){
case VM_FAULT_READONLY:
mmu_map(as, va, pa, 0);
break;
case VM_FAULT_READ:
case VM_FAULT_WRITE:
// Set it to dirty
LP_SET(lp, LPF_DIRTY);
mmu_map(as, va, pa, 1);
}
// Already unpinned in mmu_map
lpage_unlock(lp);
return 0;
}
/*
* Locate the physical frame number for the given vaddr using the page table.
*
* If the entry is invalid and not on swap, then this is the first reference
* to the page and a (simulated) physical frame should be allocated and
* initialized (using init_frame).
*
* If the entry is invalid and on swap, then a (simulated) physical frame
* should be allocated and filled by reading the page data from swap.
*
* Counters for hit, miss and reference events should be incremented in
* this function.
*/
char *find_physpage(addr_t vaddr, char type) {
pgtbl_entry_t *p=NULL; // pointer to the full page table entry for vaddr
unsigned idx = PGDIR_INDEX(vaddr); // get index into page directory
// IMPLEMENTATION NEEDED
// Use top-level page directory to get pointer to 2nd-level page table
// Check if it's valid
unsigned int valid_pde = pgdir[idx].pde & PG_VALID;
// Not Valid, initialize a 2nd pagetable
if (!valid_pde) {
pgdir[idx] = init_second_level();
}
// Use vaddr to get index into 2nd-level page table and initialize 'p'
unsigned pgtbl_index = PGTBL_INDEX(vaddr);
p = (pgtbl_entry_t *) (pgdir[idx].pde & PAGE_MASK);
p = p + pgtbl_index;
// Check if p is valid or not, on swap or not, and handle appropriately
// Find the valid bit and the on-swap bit
unsigned int valid = p->frame & PG_VALID;
unsigned int on_swap = p->frame & PG_ONSWAP;
// Check if it's valid
if (!valid) {
// Allocate a frame for p
int frame = allocate_frame(p);
// Update fields for OPT
coremap[frame].pgtbl_idx = (int) pgtbl_index;
coremap[frame].pgdir_idx = (int) idx;
// On swap
if (on_swap) {
// Read the page from swap
int success = swap_pagein(frame, p->swap_off);
assert(success == 0);
}
// Not on swap
if (!on_swap) {
// Initialize the frame
init_frame(frame, vaddr);
// Mark it as dirty
p->frame = p->frame | PG_DIRTY;
}
// Not Valid, so increment miss
miss_count++;
}
// Make sure that p is marked valid and referenced. Also mark it
// dirty if the access type indicates that the page will be written to.
// Mark p as valid and referenced
p->frame = p->frame | PG_VALID;
p->frame = p->frame | PG_REF;
unsigned int check = p->frame & PG_VALID;
assert(check);
// Check the access type
if ((type == 'S') || (type == 'M')) {
// Set the dirty bit
p->frame = p->frame | PG_DIRTY;
}
// Increment ref, hit
if (valid) {
hit_count++;
}
ref_count++;
// Call replacement algorithm's ref_fcn for this page
ref_fcn(p);
// Return pointer into (simulated) physical memory at start of frame
return &physmem[(p->frame >> PAGE_SHIFT)*SIMPAGESIZE];
}
// Copies Logical Page from fromlp to tolp.
int
lp_copy (struct lpage *fromlp, struct lpage **tolp)
{
struct lpage *newlp = NULL;
paddr_t frompa; paddr_t topa;
off_t swapaddr;
int result;
DEBUG(DB_VM, "LPage: lp_copy\n");
lock_acquire(fromlp -> lock);
frompa = fromlp -> paddr & PAGE_FRAME;
if (frompa == INVALID_PADDR) {
swapaddr = fromlp -> swapaddr;
lock_release(fromlp -> lock);
frompa = cm_allocuserpage(fromlp);
if (frompa == INVALID_PADDR) {
return (ENOMEM);
}
KASSERT(cm_pageispinned(frompa));
lock_acquire(paging_lock);
swap_pagein(frompa, swapaddr);
lock_acquire(fromlp -> lock);
lock_release(paging_lock);
KASSERT((fromlp -> paddr & PAGE_FRAME) == INVALID_PADDR);
fromlp -> paddr = frompa | LPF_LOCKED;
}
else {
cm_pin(frompa);
}
KASSERT(cm_pageispinned(frompa));
result = lp_setup(&newlp, &topa);
if (result) {
cm_unpin(frompa);
lock_release(fromlp -> lock);
return (result);
}
KASSERT(cm_pageispinned(topa));
KASSERT(cm_pageispinned(frompa));
cm_copypage(frompa, topa);
cm_unpin(topa);
cm_unpin(frompa);
lock_release(fromlp -> lock);
lock_release(newlp -> lock);
*tolp = newlp;
return (0);
}
/*
* lpage_fault - handle a fault on a specific lpage. If the page is
* not resident, get a physical page from coremap and swap it in.
*
* You do not yet need to distinguish a readonly fault from a write
* fault. When we implement sharing, there will be a difference.
*
* Synchronization: Lock the lpage while checking if it's in memory.
* If it's not, unlock the page while allocating space and loading the
* page in. This only works because lpages are not currently sharable.
* The page should be locked again as soon as it is loaded, but be
* careful of interactions with other locks while modifying the coremap.
*
* After it has been loaded, the page must be pinned so that it is not
* evicted while changes are made to the TLB. It can be unpinned as soon
* as the TLB is updated.
*/
int
lpage_fault(struct lpage *lp, struct addrspace *as, int faulttype, vaddr_t va)
{
KASSERT(lp != NULL); // kernel pages never get paged out, thus never fault
lock_acquire(global_paging_lock);
if ((lp->lp_paddr & PAGE_FRAME) != INVALID_PADDR) {
lpage_lock_and_pin(lp);
} else {
lpage_lock(lp);
}
lock_release(global_paging_lock);
KASSERT(lp->lp_swapaddr != INVALID_SWAPADDR);
paddr_t pa = lp->lp_paddr;
int writable; // 0 if page is read-only, 1 if page is writable
/* case 1 - minor fault: the frame is still in memory */
if ((pa & PAGE_FRAME) != INVALID_PADDR) {
/* make sure it's a minor fault */
KASSERT(pa != INVALID_PADDR);
/* Setting the TLB entry's dirty bit */
writable = (faulttype != VM_FAULT_READ);
/* update stats */
spinlock_acquire(&stats_spinlock);
ct_minfaults++;
DEBUG(DB_VM, "\nlpage_fault: minor faults = %d.", ct_minfaults);
spinlock_release(&stats_spinlock);
} else {
/* case 2 - major fault: the frame was swapped out to disk */
/* make sure it is a major fault */
KASSERT(pa == INVALID_PADDR);
/* allocate a new frame */
lpage_unlock(lp); // must not hold lpage locks before entering coremap
pa = coremap_allocuser(lp); // do evict if needed, also pin coremap
if ((pa & PAGE_FRAME)== INVALID_PADDR) {
DEBUG(DB_VM, "lpage_fault: ENOMEM: va=0x%x\n", va);
return ENOMEM;
}
KASSERT(coremap_pageispinned(pa));
/* retrieving the content from disk */
lock_acquire(global_paging_lock); // because swap_pagein needs it
swap_pagein((pa & PAGE_FRAME), lp->lp_swapaddr); // coremap is already pinned above
lpage_lock(lp);
lock_release(global_paging_lock);
/* assert that nobody else did the pagein */
KASSERT((lp->lp_paddr & PAGE_FRAME) == INVALID_PADDR);
/* now update PTE with new PFN */
lp->lp_paddr = pa ; // page is clean
/* Setting the TLB entry's dirty bit */
writable = 0; // this way we can detect the first write to a page
/* update stats */
spinlock_acquire(&stats_spinlock);
ct_majfaults++;
DEBUG(DB_VM, "\nlpage_fault: MAJOR faults = %d", ct_majfaults);
spinlock_release(&stats_spinlock);
}
/* check preconditions before update TLB/PTE */
KASSERT(coremap_pageispinned(lp->lp_paddr));
KASSERT(spinlock_do_i_hold(&lp->lp_spinlock));
/* PTE entry is dirty if the instruction is a write */
if (writable) {
LP_SET(lp, LPF_DIRTY);
}
/* Put the new TLB entry into the TLB */
KASSERT(coremap_pageispinned(lp->lp_paddr)); // done in both cases of above IF clause
mmu_map(as, va, lp->lp_paddr, writable); // update TLB and unpin coremap
lpage_unlock(lp);
return 0;
}
/*
* lpage_copy: create a new lpage and copy data from another lpage.
*
* The synchronization for this is kind of unpleasant. We do it like
* this:
*
* 1. Create newlp.
* 2. Materialize a page for newlp, so it's locked and pinned.
* 3. Lock and pin oldlp.
* 4. Extract the physical address and swap address.
* 5. If oldlp wasn't present,
* 5a. Unlock oldlp.
* 5b. Page in.
* 5c. This pins the page in the coremap.
* 5d. Leave the page pinned and relock oldlp.
* 5e. Assert nobody else paged the page in.
* 6. Copy.
* 7. Unlock the lpages first, so we can enter the coremap.
* 8. Unpin the physical pages.
*
*/
int
lpage_copy(struct lpage *oldlp, struct lpage **lpret)
{
struct lpage *newlp;
paddr_t newpa, oldpa;
off_t swa;
int result;
result = lpage_materialize(&newlp, &newpa);
if (result) {
return result;
}
KASSERT(coremap_pageispinned(newpa));
/* Pin the physical page and lock the lpage. */
lpage_lock_and_pin(oldlp);
oldpa = oldlp->lp_paddr & PAGE_FRAME;
/*
* If there is no physical page, we allocate one, which pins
* it, and then (re)lock the lpage. Since we are single-
* threaded (if we weren't, we'd hold the address space lock
* to exclude sibling threads) nobody else should have paged
* the page in behind our back.
*/
if (oldpa == INVALID_PADDR) {
/*
* XXX this is mostly copied from lpage_fault
*/
swa = oldlp->lp_swapaddr;
lpage_unlock(oldlp);
oldpa = coremap_allocuser(oldlp);
if (oldpa == INVALID_PADDR) {
coremap_unpin(newlp->lp_paddr & PAGE_FRAME);
lpage_destroy(newlp);
return ENOMEM;
}
KASSERT(coremap_pageispinned(oldpa));
lock_acquire(global_paging_lock);
swap_pagein(oldpa, swa);
lpage_lock(oldlp);
lock_release(global_paging_lock);
/* Assert nobody else did the pagein. */
KASSERT((oldlp->lp_paddr & PAGE_FRAME) == INVALID_PADDR);
oldlp->lp_paddr = oldpa;
}
KASSERT(coremap_pageispinned(oldpa));
coremap_copy_page(oldpa, newpa);
KASSERT(LP_ISDIRTY(newlp));
lpage_unlock(oldlp);
lpage_unlock(newlp);
coremap_unpin(newpa);
coremap_unpin(oldpa);
*lpret = newlp;
return 0;
}
