vm: Copy on write

include/sys/vm_amap.h

@@ -1,45 +1,116 @@
 #ifndef _SYS_VM_AMAP_H_
 #define _SYS_VM_AMAP_H_
 
+#include <sys/mutex.h>
+#include <sys/refcnt.h>
 #include <sys/types.h>
 #include <sys/vm.h>
 #include <stddef.h>
 
 typedef struct vm_amap vm_amap_t;
+typedef struct vm_anon vm_anon_t;
 typedef struct vm_aref vm_aref_t;
 
+/* Anon structure
+ *
+ * Marks for fields locks:
+ *  (a) atomic
+ *  (!) read-only access, do not modify!
+ */
+struct vm_anon {
+  refcnt_t ref_cnt; /* (a) number of references */
+  vm_page_t *page;  /* (!) anon page */
+};
+
 struct vm_aref {
   size_t offset;   /* offset in slots */
   vm_amap_t *amap; /* underlying amap */
 };
 
-/*
- * Allocate new amap with specified number of slots.
+/** Allocate new amap.
  *
- * Always returns new amap with ref_cnt equal to 1.
+ * The size of new amap is determined using `slots`.
+ *
+ * @returns New amap with ref_cnt = 1.
  */
 vm_amap_t *vm_amap_alloc(size_t slots);
 
-/*
+/** Clone the amap.
+ *
  * Create new amap with contents matching old amap. Starting from offset
  * specified by aref and copying specified number of slots.
  *
- * Always returns new amap with ref_cnt equal to 1.
+ * @returns New amap with ref_cnt = 1.
  */
 vm_amap_t *vm_amap_clone(vm_aref_t aref, size_t slots);
 
-/* Bump the ref counter to record that amap is used by next one entry. */
+/** Copy amap when it is needed.
+ *
+ * Amap is actually copied is referenced by more then one vm_map_entries.
+ * Otherwise nothing is done and old aref is returned.
+ *
+ * @returns Aref ready to use
+ */
+vm_aref_t vm_amap_needs_copy(vm_aref_t aref, size_t slots);
+
+/** Bump the ref counter to record that amap is used by next one entry. */
 void vm_amap_hold(vm_amap_t *amap);
 
-/* Drop ref counter and possibly free amap if it drops to 0. */
+/** Drop ref counter and possibly free amap if it drops to 0. */
 void vm_amap_drop(vm_amap_t *amap);
 
-vm_page_t *vm_amap_find_page(vm_aref_t aref, size_t offset);
-int vm_amap_add_page(vm_aref_t aref, vm_page_t *frame, size_t offset);
+/** Remove multiple pages from amap
+ *
+ * @param offset Start from this offset in amap.
+ * @param n_slots Remove that many pages (anons).
+ */
 void vm_amap_remove_pages(vm_aref_t aref, size_t offset, size_t n_slots);
 
-/* Functions accessing amap's internal data */
+/** Get amap reference count */
 int vm_amap_ref(vm_amap_t *amap);
+
+/** Get amap max size (in slots) */
 size_t vm_amap_slots(vm_amap_t *amap);
 
+/** Alloc new anon.
+ *
+ * @retval != NULL Anon with zeroed page and ref_cnt = 1.
+ * @retval NULL If anon's page can't be allocate.
+ */
+vm_anon_t *vm_anon_alloc(void);
+
+/** Copy anon.
+ *
+ * NOTE: Don't decrease ref_cnt of src.
+ *
+ * @retval != NULL Anon with ref_cnt = 1.
+ * @retval NULL If anon's page can't be allocate.
+ */
+vm_anon_t *vm_anon_copy(vm_anon_t *src);
+
+/** Find anon in amap.
+ *
+ * @returns Found anon or NULL.
+ */
+vm_anon_t *vm_amap_find_anon(vm_aref_t aref, size_t offset);
+
+/** Insert anon into amap
+ *
+ * If anon was already present at given offset it will be replaced and returned
+ * from this function.
+ *
+ * @retval NULL Anon was inserted
+ * @retval != NULL Anon that was previously at that offset.
+ * */
+vm_anon_t *vm_amap_insert_anon(vm_aref_t aref, vm_anon_t *anon, size_t offset);
+
+/** Replace anon in amap with new one. */
+void vm_amap_replace_anon(vm_aref_t aref, vm_anon_t *anon, size_t offset);
+
+/** Bump the ref counter to record that anon is used by one more amap. */
+void vm_anon_hold(vm_anon_t *anon);
+
+/** Drop ref counter and possibly free anon if it drops to 0. */
+void vm_anon_drop(vm_anon_t *anon);
+
 #endif /* !_SYS_VM_AMAP_H_ */

include/sys/vm_map.h

@@ -11,8 +11,10 @@ typedef struct vm_map vm_map_t;
 typedef struct vm_map_entry vm_map_entry_t;
 
 typedef enum {
-  VM_ENT_SHARED = 1,  /* shared memory */
-  VM_ENT_PRIVATE = 2, /* private memory (default) */
+  VM_ENT_SHARED = 1,    /* shared memory */
+  VM_ENT_PRIVATE = 2,   /* private memory (default) */
+  VM_ENT_COW = 4,       /* copy on write */
+  VM_ENT_NEEDSCOPY = 8, /* amap needs copy */
 } vm_entry_flags_t;
 
 /*! \brief Called during kernel initialization. */

sys/gen/pmap.c

@@ -457,9 +457,6 @@ int pmap_fault_handler(ctx_t *ctx, vaddr_t vaddr, vm_prot_t access) {
   if (!(error = pmap_emulate_bits(pmap, vaddr, access)))
     return 0;
 
-  if (error == EACCES)
-    goto fault;
-
   vm_map_t *vmap = vm_map_user();
 
   if (!(error = vm_page_fault(vmap, vaddr, access)))