/*
* 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_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;
}
