ПЛР3 P3331 Дворкин Борис Части 1-4

xv6-os/ci/test/main.py

@@ -40,7 +40,14 @@ def read_header(qemu: Qemu):
     assert_eq(prefix[3], "")
     assert prefix[4] in (f"hart {i + 1} starting" for i in range(2))
     assert prefix[5] in (f"hart {i + 1} starting" for i in range(2))
-    assert_eq(prefix[6], "init: starting sh")
+    # lab-3 dumps the initial page table (vmprint) at boot before the shell
+    # starts; skip any such lines until the shell banner appears.
+    line = prefix[6]
+    for _ in range(256):
+        if line == "init: starting sh":
+            break
+        line = qemu.readline()
+    assert_eq(line, "init: starting sh")
 
 
 if __name__ == "__main__":

xv6-os/ci/test/suite/usertests.py

@@ -57,41 +57,18 @@
     Xv6UserTest(name="forktest", timeout=timedelta(seconds=1)),
     Xv6UserTest(name="sbrkbasic", timeout=timedelta(seconds=3)),
     Xv6UserTest(name="sbrkmuch", timeout=timedelta(seconds=2)),
-    Xv6UserTest(
-        name="kernmem",
-        timeout=timedelta(milliseconds=500),
-        suffix_size=len("usertrap(): unexpected scause 0xd pid=6452"),
-        extra_lines=79,
-    ),
-    Xv6UserTest(
-        name="MAXVAplus",
-        timeout=timedelta(seconds=30),
-        suffix_size=len("usertrap(): unexpected scause 0xf pid=6515"),
-        extra_lines=51,
-    ),
-    Xv6UserTest(
-        name="sbrkfail",
-        timeout=timedelta(seconds=8),
-        suffix_size=len("usertrap(): unexpected scause 0xd pid=6553"),
-        extra_lines=1,
-    ),
+    # CoW handles page faults (scause 13/15) and kills the process silently,
+    # so these tests print only "test <name>: OK" without the usertrap dump.
+    Xv6UserTest(name="kernmem", timeout=timedelta(milliseconds=500)),
+    Xv6UserTest(name="MAXVAplus", timeout=timedelta(seconds=30)),
+    Xv6UserTest(name="sbrkfail", timeout=timedelta(seconds=8)),
     Xv6UserTest(name="sbrkarg", timeout=timedelta(seconds=2)),
     Xv6UserTest(name="validatetest", timeout=timedelta(seconds=2)),
     Xv6UserTest(name="bsstest", timeout=timedelta(seconds=2)),
     Xv6UserTest(name="bigargtest", timeout=timedelta(seconds=2)),
     Xv6UserTest(name="argptest", timeout=timedelta(seconds=2)),
-    Xv6UserTest(
-        name="stacktest",
-        timeout=timedelta(seconds=2),
-        suffix_size=len("usertrap(): unexpected scause 0xd pid=6561"),
-        extra_lines=1,
-    ),
-    Xv6UserTest(
-        name="nowrite",
-        timeout=timedelta(seconds=2),
-        suffix_size=len("usertrap(): unexpected scause 0xf pid=6563"),
-        extra_lines=11,
-    ),
+    Xv6UserTest(name="stacktest", timeout=timedelta(seconds=2)),
+    Xv6UserTest(name="nowrite", timeout=timedelta(seconds=2)),
     Xv6UserTest(name="pgbug", timeout=timedelta(seconds=2)),
     Xv6UserTest(
         name="sbrkbugs",

xv6-os/kernel/defs.h

@@ -64,6 +64,8 @@ void            ramdiskrw(struct buf*);
 void*           kalloc(void);
 void            kfree(void *);
 void            kinit(void);
+void            inc_refcount(void *);
+uint            get_refcount(void *);
 
 // log.c
 void            initlog(int, struct superblock*);
@@ -174,6 +176,8 @@ uint64          walkaddr(pagetable_t, uint64);
 int             copyout(pagetable_t, uint64, char *, uint64);
 int             copyin(pagetable_t, char *, uint64, uint64);
 int             copyinstr(pagetable_t, char *, uint64, uint64);
+int             cowalloc(pagetable_t, uint64);
+void            vmprint(pagetable_t);
 
 // plic.c
 void            plicinit(void);

xv6-os/kernel/exec.c

@@ -128,6 +128,9 @@ exec(char *path, char **argv)
   p->trapframe->sp = sp; // initial stack pointer
   proc_freepagetable(oldpagetable, oldsz);
 
+  if(p->pid == 1)
+    vmprint(pagetable);
+
   return argc; // this ends up in a0, the first argument to main(argc, argv)
 
  bad:

xv6-os/kernel/kalloc.c

@@ -21,6 +21,7 @@ struct run {
 struct {
   struct spinlock lock;
   struct run *freelist;
+  uint refcount[PHYSTOP / PGSIZE];
 } kmem;
 
 void
@@ -35,8 +36,11 @@ freerange(void *pa_start, void *pa_end)
 {
   char *p;
   p = (char*)PGROUNDUP((uint64)pa_start);
-  for(; p + PGSIZE <= (char*)pa_end; p += PGSIZE)
+  for(; p + PGSIZE <= (char*)pa_end; p += PGSIZE) {
+    int pindex = (uint64)p / PGSIZE;
+    kmem.refcount[pindex] = 1;
     kfree(p);
+  }
 }
 
 // Free the page of physical memory pointed at by pa,
@@ -51,6 +55,17 @@ kfree(void *pa)
   if(((uint64)pa % PGSIZE) != 0 || (char*)pa < end || (uint64)pa >= PHYSTOP)
     panic("kfree");
 
+  acquire(&kmem.lock);
+  int pindex = (uint64)pa / PGSIZE;
+  if(kmem.refcount[pindex] == 0)
+    panic("kfree refcount");
+  kmem.refcount[pindex]--;
+  int current_refcount = kmem.refcount[pindex];
+  release(&kmem.lock);
+
+  if(current_refcount > 0)
+    return;
+
   // Fill with junk to catch dangling refs.
   memset(pa, 1, PGSIZE);
 
@@ -72,11 +87,42 @@ kalloc(void)
 
   acquire(&kmem.lock);
   r = kmem.freelist;
-  if(r)
+  if(r) {
     kmem.freelist = r->next;
+    int pindex = (uint64)r / PGSIZE;
+
+    if(kmem.refcount[pindex] > 0)
+      panic("kalloc");
+
+    kmem.refcount[pindex] = 1;
+  }
   release(&kmem.lock);
 
   if(r)
     memset((char*)r, 5, PGSIZE); // fill with junk
   return (void*)r;
 }
+
+void
+inc_refcount(void *pa)
+{
+  if(((uint64)pa % PGSIZE) != 0 || (char*)pa < end || (uint64)pa >= PHYSTOP)
+    panic("inc_refcount");
+
+  acquire(&kmem.lock);
+  int pindex = (uint64)pa / PGSIZE;
+  if(kmem.refcount[pindex] == 0)
+    panic("inc_refcount");
+  kmem.refcount[pindex]++;
+  release(&kmem.lock);
+}
+
+uint 
+get_refcount(void *pa)
+{
+  acquire(&kmem.lock);
+  int pindex = (uint64)pa / PGSIZE;
+  uint curr_refcount = kmem.refcount[pindex];
+  release(&kmem.lock);
+  return curr_refcount;
+}

xv6-os/kernel/riscv.h

@@ -358,6 +358,7 @@ typedef uint64 *pagetable_t; // 512 PTEs
 #define PTE_W (1L << 2)
 #define PTE_X (1L << 3)
 #define PTE_U (1L << 4) // user can access
+#define PTE_RSW (1L << 8)
 
 // shift a physical address to the right place for a PTE.
 #define PA2PTE(pa) ((((uint64)pa) >> 12) << 10)

xv6-os/kernel/trap.c

@@ -65,6 +65,12 @@ usertrap(void)
     intr_on();
 
     syscall();
+  } else if(r_scause() == 13 || r_scause() == 15) {
+    uint64 va = PGROUNDDOWN(r_stval());
+
+    if(cowalloc(p->pagetable, va) == -1) {
+      setkilled(p);
+    }
   } else if((which_dev = devintr()) != 0){
     // ok
   } else {

xv6-os/kernel/vm.c

@@ -315,7 +315,6 @@ uvmcopy(pagetable_t old, pagetable_t new, uint64 sz)
   pte_t *pte;
   uint64 pa, i;
   uint flags;
-  char *mem;
 
   for(i = 0; i < sz; i += PGSIZE){
     if((pte = walk(old, i, 0)) == 0)
@@ -324,13 +323,19 @@ uvmcopy(pagetable_t old, pagetable_t new, uint64 sz)
       panic("uvmcopy: page not present");
     pa = PTE2PA(*pte);
     flags = PTE_FLAGS(*pte);
-    if((mem = kalloc()) == 0)
-      goto err;
-    memmove(mem, (char*)pa, PGSIZE);
-    if(mappages(new, i, PGSIZE, (uint64)mem, flags) != 0){
-      kfree(mem);
+
+    if((flags & PTE_W) != 0) 
+      flags =  (flags & (~PTE_W)) | PTE_RSW;
+
+
+    if(mappages(new, i, PGSIZE, (uint64)pa, flags) != 0){
       goto err;
     }
+
+    if((*pte& PTE_W) != 0)
+      *pte = (*pte & (~PTE_W)) | PTE_RSW;
+
+    inc_refcount((void*)pa);
   }
   return 0;
 
@@ -339,6 +344,42 @@ uvmcopy(pagetable_t old, pagetable_t new, uint64 sz)
   return -1;
 }
 
+int
+cowalloc(pagetable_t pagetable, uint64 va)
+{
+  if(va >= MAXVA || va % PGSIZE != 0)
+    return -1;
+
+  pte_t *pte;
+  if ((pte = walk(pagetable, va, 0)) == 0)
+    return -1;
+
+  if((*pte & PTE_U) == 0 || (*pte & PTE_V) == 0 || (*pte & PTE_RSW) == 0)
+    return -1;
+
+  uint64 old_pa = PTE2PA(*pte);
+
+  if(get_refcount((void*)old_pa) == 1) {
+    *pte = (*pte & (~PTE_RSW)) | PTE_W;
+    return 0;
+  }
+
+  uint64 new_pa = (uint64)kalloc();
+  if(new_pa == 0)
+    return -1;
+
+  uint flags = PTE_FLAGS(*pte);
+  flags = (flags & (~PTE_RSW)) | PTE_W;
+
+  memmove((void*)new_pa, (void*)old_pa, PGSIZE);
+  uvmunmap(pagetable, va, 1, 0);
+  mappages(pagetable, va, PGSIZE, new_pa, flags);
+
+  kfree((void *)old_pa);
+
+  return 0;
+}
+
 // mark a PTE invalid for user access.
 // used by exec for the user stack guard page.
 void
@@ -366,9 +407,13 @@ copyout(pagetable_t pagetable, uint64 dstva, char *src, uint64 len)
     if(va0 >= MAXVA)
       return -1;
     pte = walk(pagetable, va0, 0);
-    if(pte == 0 || (*pte & PTE_V) == 0 || (*pte & PTE_U) == 0 ||
-       (*pte & PTE_W) == 0)
+    if(pte == 0 || (*pte & PTE_V) == 0 || (*pte & PTE_U) == 0)
       return -1;
+
+    if ((*pte & PTE_W) == 0 && cowalloc(pagetable, va0) == -1) {
+      return -1;
+    }
+
     pa0 = PTE2PA(*pte);
     n = PGSIZE - (dstva - va0);
     if(n > len)
@@ -449,3 +494,37 @@ copyinstr(pagetable_t pagetable, char *dst, uint64 srcva, uint64 max)
     return -1;
   }
 }
+
+#define PT_SIZE 512
+
+void
+vmprinttable(pagetable_t pagetable, int level)
+{
+  for (int i = 0; i < PT_SIZE; i++) {
+    pagetable_t temp_pagetable = pagetable;
+    pte_t pte = temp_pagetable[i];
+
+    if (!(pte & PTE_V))
+      continue;;
+
+    for (int j = 0; j <= 2 - level; j++) {
+      printf("..");
+      if (j != 2 - level)
+        printf(" ");
+    }
+    printf("%d ", i);
+
+    printf("pte %p pa %p\n", (void *) pte, (void *) PTE2PA(pte));
+
+    if (level != 0)
+      vmprinttable((pagetable_t) PTE2PA(pte), level-1);
+  }
+}
+
+void 
+vmprint(pagetable_t pagetable) 
+{
+  printf("page table %p\n", pagetable);
+
+  vmprinttable(pagetable, 2);  
+}