/*
* lpage_destroy: deallocates a logical page. Releases any RAM or swap
* pages involved.
*
* Synchronization: Someone might be in the process of evicting the
* page if it's resident, so it might be pinned. So lock and pin
* together.
*
* We assume that lpages are not shared between address spaces and
* address spaces are not shared between threads.
*/
void
lpage_destroy(struct lpage *lp)
{
paddr_t pa;
KASSERT(lp != NULL);
lpage_lock_and_pin(lp);
pa = lp->lp_paddr & PAGE_FRAME;
if (pa != INVALID_PADDR) {
DEBUG(DB_VM, "lpage_destroy: freeing paddr 0x%x\n", pa);
lp->lp_paddr = INVALID_PADDR;
lpage_unlock(lp);
coremap_free(pa, false /* iskern */);
coremap_unpin(pa);
}
else {
lpage_unlock(lp);
}
if (lp->lp_swapaddr != INVALID_SWAPADDR) {
DEBUG(DB_VM, "lpage_destroy: freeing swap addr 0x%llx\n",
lp->lp_swapaddr);
swap_free(lp->lp_swapaddr);
}
spinlock_cleanup(&lp->lp_spinlock);
kfree(lp);
}
/*
* 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;
}
/*
* lpage_zerofill: create a new lpage and arrange for it to be cleared
* to all zeros. The current implementation causes the lpage to be
* resident upon return, but this is not a guaranteed property, and
* nothing prevents the page from being evicted before it is used by
* the caller.
*
* Synchronization: coremap_allocuser returns the new physical page
* "pinned" (locked) - we hold that lock while we update the page
* contents and the necessary lpage fields. Unlock the lpage before
* unpinning, so it's safe to take the coremap spinlock.
*/
int
lpage_zerofill(struct lpage **lpret)
{
struct lpage *lp;
paddr_t pa;
int result;
result = lpage_materialize(&lp, &pa);
if (result) {
return result;
}
KASSERT(spinlock_do_i_hold(&lp->lp_spinlock));
KASSERT(coremap_pageispinned(pa));
/* Don't actually need the lpage locked. */
lpage_unlock(lp);
coremap_zero_page(pa);
KASSERT(coremap_pageispinned(pa));
coremap_unpin(pa);
spinlock_acquire(&stats_spinlock);
ct_zerofills++;
spinlock_release(&stats_spinlock);
*lpret = lp;
return 0;
}
/*
* lpage_evict: Evict an lpage from physical memory.
*
* Synchronization: lock the lpage while evicting it. We come here
* from the coremap and should
* have pinned the physical page. This is why we must not hold lpage
* locks while entering the coremap code.
*/
void
lpage_evict(struct lpage *lp)
{
KASSERT(lp != NULL);
lpage_lock(lp);
KASSERT(lp->lp_paddr != INVALID_PADDR);
KASSERT(lp->lp_swapaddr != INVALID_SWAPADDR);
/* if the page is dirty, swap_pageout */
if (LP_ISDIRTY(lp)) {
lpage_unlock(lp); // release lock before doing I/O
KASSERT(lock_do_i_hold(global_paging_lock));
KASSERT(coremap_pageispinned(lp->lp_paddr));
swap_pageout((lp->lp_paddr & PAGE_FRAME), lp->lp_swapaddr);
lpage_lock(lp);
KASSERT((lp->lp_paddr & PAGE_FRAME) != INVALID_PADDR);
/* update stats */
spinlock_acquire(&stats_spinlock);
ct_write_evictions++;
DEBUG (DB_VM, "lpage_evict: evicting Dirty page 0x%x\n",
(lp->lp_paddr & PAGE_FRAME));
spinlock_release(&stats_spinlock);
} else {
/* if page is clean, just update stats */
spinlock_acquire(&stats_spinlock);
ct_discard_evictions++;
DEBUG (DB_VM, "lpage_evict: evicting Clean page 0x%x\n",
(lp->lp_paddr & PAGE_FRAME));
spinlock_release(&stats_spinlock);
}
/* modify PTE to indicate that the page is no longer in memory. */
lp->lp_paddr = INVALID_PADDR;
lpage_unlock(lp);
}
/*
* lpage_evict: Evict an lpage from physical memory.
*
* Synchronization: lock the lpage while accessing it. We come here
* from the coremap and should have the global paging lock and should
* have pinned the physical page (see coremap.c:do_evict()).
* This is why we must not hold lpage locks while entering the coremap code.
*
* Similar to lpage_fault, the lpage lock should not be held while performing
* the page out (if one is needed).
*/
void
lpage_evict(struct lpage *lp)
{
paddr_t pa;
off_t swapaddr;
KASSERT(lock_do_i_hold(global_paging_lock));
KASSERT(lp != NULL);
lpage_lock(lp);
swapaddr = lp->lp_swapaddr;
pa = lp->lp_paddr & PAGE_FRAME;
KASSERT(pa != INVALID_PADDR);
if (LP_ISDIRTY(lp)) {
lpage_unlock(lp);
LP_CLEAR(lp, LPF_DIRTY);
swap_pageout(pa, swapaddr);
lpage_lock(lp);
}
lp->lp_paddr = INVALID_PADDR;
lpage_unlock(lp);
}
/*
* lpage_evict: Evict an lpage from physical memory.
*
* Synchronization: lock the lpage while accessing it. We come here
* from the coremap and should have the global paging lock and should
* have pinned the physical page (see coremap.c:do_evict()).
* This is why we must not hold lpage locks while entering the coremap code.
*
* Similar to lpage_fault, the lpage lock should not be held while performing
* the page out (if one is needed).
*/
void
lpage_evict(struct lpage *lp)
{
paddr_t physical_address;
off_t swap_address;
// Lock the lpage while accessing it.
KASSERT(lp != NULL);
lpage_lock(lp);
// Obtain the physical & swap address'
physical_address = lp->lp_paddr & PAGE_FRAME;
swap_address = lp->lp_swapaddr;
// If the page is stored in RAM memory...
if (physical_address != INVALID_PADDR) {
DEBUG(DB_VM, "lpage_evict: Moving page from paddr 0x%x to swapaddr 0x%llx\n", physical_address, swap_address);
// If page is dirty..
if (LP_ISDIRTY(lp)) {
// Move page into swapspace.
lpage_unlock(lp);
swap_pageout(physical_address, swap_address);
LP_CLEAR(lp, LPF_DIRTY);
lpage_lock(lp);
}
// Remove page from physical memory.
lp->lp_paddr = INVALID_PADDR;
lpage_unlock(lp);
}
else {
lpage_unlock(lp);
}
}
/*
* lpage_lock_and_pin
*
* Lock the lpage and also pin the underlying physical page (if any)
* in the coremap. This requires a silly retry dance, because we need
* to pin first but also need the physical address from the lpage to
* do that. If the physical address changes while we were pinning the
* page, retry.
*
* Note that you can't in general hold another lpage lock when calling
* this, because it acquires the coremap spinlock, and then perhaps
* waits to pin the physical page. The eviction path holds the coremap
* spinlock and holds a page pinned while locking the lpage; so if
* someone's trying to swap the other page out you can deadlock.
*
* However, if you've got the other lpage locked *and* its physical
* page pinned, that can't happen, so it's safe to lock and pin
* multiple pages.
*/
void
lpage_lock_and_pin(struct lpage *lp)
{
paddr_t pa, pinned;
pinned = INVALID_PADDR;
lpage_lock(lp);
while (1) {
pa = lp->lp_paddr & PAGE_FRAME;
/*
* If the lpage matches what we have (including on the
* first pass with INVALID_PADDR) we're done.
*/
if (pa == pinned) {
break;
}
/*
* Otherwise we need to unpin, which means unlock the
* lpage too.
*/
lpage_unlock(lp);
if (pinned != INVALID_PADDR) {
coremap_unpin(pinned);
}
/*
* If what we just got out of the lpage is *now*
* invalid, because the page was paged out on us,
* we're done. The page can't be paged in again behind
* our back, so assert it hasn't after regrabbing the
* lpage lock.
*/
if (pa == INVALID_PADDR) {
lpage_lock(lp);
KASSERT((lp->lp_paddr & PAGE_FRAME) == INVALID_PADDR);
break;
}
/* Pin what we got and try again. */
coremap_pin(pa);
pinned = pa;
lpage_lock(lp);
}
}
/*
* 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;
}