Slight simplification of copyuvm. We could simplify other things now that...

Slight simplification of copyuvm.  We could simplify other things now that processes are contiguous, but we'd have to think harder about the error paths.

vm.c

@@ -310,14 +310,14 @@ copyuvm(pde_t *pgdir, uint sz)
   for(i = 0; i < sz; i += PGSIZE){
     if(!(pte = walkpgdir(pgdir, (void *)i, 0)))
       panic("copyuvm: pte should exist\n");
-    if(*pte & PTE_P){
-      pa = PTE_ADDR(*pte);
-      if(!(mem = kalloc()))
-        goto bad;
-      memmove(mem, (char *)pa, PGSIZE);
-      if(!mappages(d, (void *)i, PGSIZE, PADDR(mem), PTE_W|PTE_U))
-        goto bad;
-    }
+    if(!(*pte & PTE_P))
+      panic("copyuvm: page not present\n");
+    pa = PTE_ADDR(*pte);
+    if(!(mem = kalloc()))
+      goto bad;
+    memmove(mem, (char *)pa, PGSIZE);
+    if(!mappages(d, (void *)i, PGSIZE, PADDR(mem), PTE_W|PTE_U))
+      goto bad;
   }
   return d;