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| author | Mole Shang <135e2@135e2.dev> | 2024-02-11 17:51:28 +0800 |
|---|---|---|
| committer | Mole Shang <135e2@135e2.dev> | 2024-02-11 17:51:28 +0800 |
| commit | 4a6593f1a6f666c618d303a4858c4c6d31b41c63 (patch) | |
| tree | 29d5302aec4e0f3c34a70baa9fb83c0bb35dbf7c | |
| parent | 2fe04bc8faa4bf737a86c36a8017473e84814f3b (diff) | |
| download | xv6-labs-4a6593f1a6f666c618d303a4858c4c6d31b41c63.tar.gz xv6-labs-4a6593f1a6f666c618d303a4858c4c6d31b41c63.tar.bz2 xv6-labs-4a6593f1a6f666c618d303a4858c4c6d31b41c63.zip | |
lab cow: finishcow
| -rw-r--r-- | Makefile | 1 | ||||
| -rw-r--r-- | kernel/cow.c | 30 | ||||
| -rw-r--r-- | kernel/defs.h | 5 | ||||
| -rw-r--r-- | kernel/kalloc.c | 43 | ||||
| -rw-r--r-- | kernel/riscv.h | 1 | ||||
| -rw-r--r-- | kernel/sysproc.c | 2 | ||||
| -rw-r--r-- | kernel/trap.c | 7 | ||||
| -rw-r--r-- | kernel/vm.c | 27 |
8 files changed, 107 insertions, 9 deletions
@@ -13,6 +13,7 @@ OBJS = \ $K/kalloc.o \ $K/string.o \ $K/main.o \ + $K/cow.o \ $K/vm.o \ $K/proc.o \ $K/swtch.o \ diff --git a/kernel/cow.c b/kernel/cow.c new file mode 100644 index 0000000..b3634fc --- /dev/null +++ b/kernel/cow.c @@ -0,0 +1,30 @@ +// COW pagefault handler +#include "types.h" +#include "riscv.h" +#include "defs.h" + +int +cow_handler(pagetable_t pagetable, uint64 va) +{ + // you can't really write to rediculous pointers + if(va >= MAXVA || PGROUNDDOWN(va) == 0) + return -1; + pte_t *pte = walk(pagetable, va, 0); + if(pte == 0 || (*pte & PTE_V) == 0 || (*pte & PTE_U) == 0) + return -1; + if(*pte & PTE_C){ + uint64 pa_orig = PTE2PA(*pte); + uint64 pa_new = (uint64)kalloc(); + if(pa_new == 0){ + printf("cow pagefault: kalloc failed\n"); + return -1; + } + // copy the page and add write permission + memmove((void*)pa_new, (void*)pa_orig, PGSIZE); + uint64 flags = (PTE_FLAGS(*pte) | PTE_W) & ~PTE_C; + *pte = PA2PTE(pa_new) | flags; + kfree((void*)pa_orig); + } else if ((*pte & PTE_W) == 0) + return -1; + return 0; +} diff --git a/kernel/defs.h b/kernel/defs.h index 04a0276..870c984 100644 --- a/kernel/defs.h +++ b/kernel/defs.h @@ -23,6 +23,9 @@ void consoleinit(void); void consoleintr(int); void consputc(int); +// cow.c +int cow_handler(pagetable_t, uint64); + // exec.c int exec(char*, char**); @@ -61,6 +64,8 @@ void ramdiskintr(void); void ramdiskrw(struct buf*); // kalloc.c +int refcnt_inc(uint64); +int refcnt_dec(uint64); void* kalloc(void); void kfree(void *); void kinit(void); diff --git a/kernel/kalloc.c b/kernel/kalloc.c index c2fdb86..581f0f6 100644 --- a/kernel/kalloc.c +++ b/kernel/kalloc.c @@ -23,10 +23,41 @@ struct { struct run *freelist; } kmem; +int phypg_refcnt[PHYSTOP/PGSIZE]; + +// Increase the refcnt +int +refcnt_inc(uint64 pa) +{ + acquire(&kmem.lock); + int *prefcnt = &phypg_refcnt[pa/PGSIZE]; + if(pa > PHYSTOP || *prefcnt < 1) + panic("increase refcnt"); + (*prefcnt)++; + release(&kmem.lock); + return *prefcnt; +} + +// Decrease the refcnt +int +refcnt_dec(uint64 pa) +{ + acquire(&kmem.lock); + int *prefcnt = &phypg_refcnt[pa/PGSIZE]; + if(pa > PHYSTOP || *prefcnt < 1) + panic("decrease refcnt"); + (*prefcnt)--; + release(&kmem.lock); + return *prefcnt; +} + void kinit() { initlock(&kmem.lock, "kmem"); + // init all refcnt to 1, which would later be freed to 0 by kfree() + for(uint64 p = PGROUNDUP((uint64)end); p + PGSIZE <= PHYSTOP; p += PGSIZE) + phypg_refcnt[p/PGSIZE] = 1; freerange(end, (void*)PHYSTOP); } @@ -51,6 +82,12 @@ kfree(void *pa) if(((uint64)pa % PGSIZE) != 0 || (char*)pa < end || (uint64)pa >= PHYSTOP) panic("kfree"); + refcnt_dec((uint64)pa); + + if(phypg_refcnt[(uint64)pa/PGSIZE] > 0) + // We still have refs to this phy page, do not actually free it + return; + // Fill with junk to catch dangling refs. memset(pa, 1, PGSIZE); @@ -72,8 +109,12 @@ kalloc(void) acquire(&kmem.lock); r = kmem.freelist; - if(r) + if(r){ + if(phypg_refcnt[(uint64)r/PGSIZE]) + panic("kalloc: invalid refcnt"); + phypg_refcnt[(uint64)r/PGSIZE] = 1; kmem.freelist = r->next; + } release(&kmem.lock); if(r) diff --git a/kernel/riscv.h b/kernel/riscv.h index 5ede50a..7d6eb6e 100644 --- a/kernel/riscv.h +++ b/kernel/riscv.h @@ -353,6 +353,7 @@ typedef uint64 *pagetable_t; // 512 PTEs #define PTE_X (1L << 3) #define PTE_U (1L << 4) // user can access #define PTE_A (1L << 6) // riscv access bit +#define PTE_C (1L << 8) // RSW low bit, use it to mark whether a page is COW // shift a physical address to the right place for a PTE. #define PA2PTE(pa) ((((uint64)pa) >> 12) << 10) diff --git a/kernel/sysproc.c b/kernel/sysproc.c index fac1d83..715a511 100644 --- a/kernel/sysproc.c +++ b/kernel/sysproc.c @@ -66,7 +66,7 @@ sys_sleep(void) sleep(&ticks, &tickslock); } - backtrace(); + // backtrace(); release(&tickslock); return 0; diff --git a/kernel/trap.c b/kernel/trap.c index eb8009f..bd3b100 100644 --- a/kernel/trap.c +++ b/kernel/trap.c @@ -73,9 +73,16 @@ usertrap(void) syscall(); } else if((which_dev = devintr()) != 0){ // ok + } else if(r_scause() == 13 || r_scause() == 15){ + // deal with page fault + uint64 va = r_stval(); + if(cow_handler(p->pagetable, va) < 0) + goto err; } else { printf("usertrap(): unexpected scause %p pid=%d\n", r_scause(), p->pid); printf(" sepc=%p stval=%p\n", r_sepc(), r_stval()); + err: + printf("killing the process...\n"); setkilled(p); } diff --git a/kernel/vm.c b/kernel/vm.c index 9c17fe7..11f9e0a 100644 --- a/kernel/vm.c +++ b/kernel/vm.c @@ -315,20 +315,26 @@ uvmcopy(pagetable_t old, pagetable_t new, uint64 sz) pte_t *pte; uint64 pa, i; uint flags; - char *mem; + // char *mem; for(i = 0; i < sz; i += PGSIZE){ if((pte = walk(old, i, 0)) == 0) panic("uvmcopy: pte should exist"); if((*pte & PTE_V) == 0) panic("uvmcopy: page not present"); - pa = PTE2PA(*pte); - flags = PTE_FLAGS(*pte); + // do not do the actual copy, just increase the refcnt and mark pages readonly COW + /* if((mem = kalloc()) == 0) goto err; memmove(mem, (char*)pa, PGSIZE); - if(mappages(new, i, PGSIZE, (uint64)mem, flags) != 0){ - kfree(mem); + */ + *pte &= ~PTE_W; + *pte |= PTE_C; + pa = PTE2PA(*pte); + refcnt_inc(pa); + flags = PTE_FLAGS(*pte); + if(mappages(new, i, PGSIZE, (uint64)pa, flags) != 0){ + // kfree(mem); goto err; } } @@ -359,17 +365,24 @@ int copyout(pagetable_t pagetable, uint64 dstva, char *src, uint64 len) { uint64 n, va0, pa0; - pte_t *pte; + // pte_t *pte; while(len > 0){ va0 = PGROUNDDOWN(dstva); - if(va0 >= MAXVA) + + if(cow_handler(pagetable, va0) < 0) return -1; + + /* pte = walk(pagetable, va0, 0); if(pte == 0 || (*pte & PTE_V) == 0 || (*pte & PTE_U) == 0 || (*pte & PTE_W) == 0) return -1; pa0 = PTE2PA(*pte); + */ + pa0 = walkaddr(pagetable, va0); + if(pa0 == 0) + return -1; n = PGSIZE - (dstva - va0); if(n > len) n = len; |