cowtest passed

kernel/vm.c

@@ -5,6 +5,8 @@
 #include "riscv.h"
 #include "defs.h"
 #include "fs.h"
+#include "proc.h"
+#include "spinlock.h"
 
 /*
  * the kernel's page table.
@@ -309,13 +311,14 @@ uvmfree(pagetable_t pagetable, uint64 sz)
 // physical memory.
 // returns 0 on success, -1 on failure.
 // frees any allocated pages on failure.
+// 如果父进程的一个 PTE 本身就是不可写的，则没有必要PTE_COW
+// 因为子进程对这块物理页也一定是不可写的，那么就没必要复制，因此只有当父进程的 PTE_W 标记时，才去附加 PTE_COW。
 int
 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)
@@ -323,14 +326,20 @@ uvmcopy(pagetable_t old, pagetable_t new, uint64 sz)
     if((*pte & PTE_V) == 0)
       panic("uvmcopy: page not present");
     pa = PTE2PA(*pte);
+
+    // lab5: Copy on write
+    // father
+    // 如果该页本身就不可写，那么子进程肯定也不可写，不用对其考虑COW
+    if(*pte & PTE_W){  
+        *pte &= ~PTE_W;
+        *pte |= PTE_COW;
+    }
     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);
+    // child
+    if(mappages(new, i, PGSIZE, (uint64)pa, flags) != 0){
       goto err;
     }
+    reference_operation((void*)pa, PLUS);
   }
   return 0;
 
@@ -338,7 +347,6 @@ uvmcopy(pagetable_t old, pagetable_t new, uint64 sz)
   uvmunmap(new, 0, i / PGSIZE, 1);
   return -1;
 }
-
 // mark a PTE invalid for user access.
 // used by exec for the user stack guard page.
 void
@@ -352,35 +360,6 @@ uvmclear(pagetable_t pagetable, uint64 va)
   *pte &= ~PTE_U;
 }
 
-// Copy from kernel to user.
-// Copy len bytes from src to virtual address dstva in a given page table.
-// Return 0 on success, -1 on error.
-int
-copyout(pagetable_t pagetable, uint64 dstva, char *src, uint64 len)
-{
-  uint64 n, va0, pa0;
-  pte_t *pte;
-
-  while(len > 0){
-    va0 = PGROUNDDOWN(dstva);
-    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)
-      return -1;
-    pa0 = PTE2PA(*pte);
-    n = PGSIZE - (dstva - va0);
-    if(n > len)
-      n = len;
-    memmove((void *)(pa0 + (dstva - va0)), src, n);
-
-    len -= n;
-    src += n;
-    dstva = va0 + PGSIZE;
-  }
-  return 0;
-}
 
 // Copy from user to kernel.
 // Copy len bytes to dst from virtual address srcva in a given page table.
@@ -449,3 +428,75 @@ copyinstr(pagetable_t pagetable, char *dst, uint64 srcva, uint64 max)
     return -1;
   }
 }
+
+// 检查是否为cowpage
+int
+iscowpage(uint64 va){
+  struct proc* p = myproc();
+  va = PGROUNDDOWN((uint64)va);
+  if(va >= MAXVA)  // 要在walk之前
+    return 0;
+  pte_t* pte = walk(p->pagetable,va,0);
+  if(pte == 0)
+    return 0;
+  if((va < p->sz)&& (*pte & PTE_COW) && (*pte & PTE_V))
+    return 1;
+  else
+    return 0;
+}
+
+// cow 的主要操作，将该 PTE 重新映射至新的物理内存，并修改flag
+void
+startcowcopy(uint64 va){
+  struct proc* p = myproc();
+  va = PGROUNDDOWN((uint64)va);
+  pte_t* pte = walk(p->pagetable,va,0);
+  uint64 pa = PTE2PA(*pte);
+
+  void* new = cowcopy_pa((void*)pa);
+  if((uint64)new == 0){
+    panic("cowcopy_pa err\n");
+    exit(-1);
+  }
+
+  uint64 flags = (PTE_FLAGS(*pte) | PTE_W) & (~PTE_COW);
+  // 确保PTE_U没有丢失
+  if (!(flags & PTE_U)) flags |= PTE_U;
+  uvmunmap(p->pagetable, va, 1, 0);  // 不包含kfree，因为ref--在cowcopy_pa中已经进行了
+
+  if(mappages(p->pagetable, va, PGSIZE, (uint64)new, flags) == -1){
+    kfree(new);
+    panic("cow mappages failed");
+  }
+}
+
+// Copy from kernel to user.
+// Copy len bytes from src to virtual address dstva in a given page table.
+// Return 0 on success, -1 on error.
+int
+copyout(pagetable_t pagetable, uint64 dstva, char *src, uint64 len)
+{
+  uint64 n, va0, pa0;
+
+  while(len > 0){
+    va0 = PGROUNDDOWN(dstva);
+    pa0 = walkaddr(pagetable, va0);
+    if(pa0 == 0)
+      return -1;
+
+    if(iscowpage(va0)){                
+      startcowcopy(va0);              
+      pa0 = walkaddr(pagetable, va0);
+    }                               
+
+    n = PGSIZE - (dstva - va0);
+    if(n > len)
+      n = len;
+    memmove((void *)(pa0 + (dstva - va0)), src, n);
+
+    len -= n;
+    src += n;
+    dstva = va0 + PGSIZE;
+  }
+  return 0;
+}