vm: controller: add an auto-detach flag for vm-objects

include/kernel/vm-object.h

@@ -14,19 +14,25 @@ enum vm_object_flags {
 	VMO_IN_PLACE = 0x01u,
 	/* this vm-object is/was attached to a vm-controller */
 	VMO_CONTROLLER = 0x02u,
+	/* when a vm-object is attached to a controller, and the ref-count of
+	 * the object falls to one (i.e. the last reference is the handle to
+	 * the object held by the server that created it), the object will
+	 * be detached, allowing the server to close the last handle to the
+	 * object and dispose of it. */
+	VMO_AUTO_DETACH = 0x04u,
 
 	/* these flags are for use with vm_object_get_page */
 	/**************************************************/
 
 	/* if the relevant page hasn't been allocated yet, it will be allocated
 	 * and returned. if this flag isn't specified, NULL will be returned. */
-	VMO_ALLOCATE_MISSING_PAGE = 0x04u,
+	VMO_ALLOCATE_MISSING_PAGE = 0x08u,
 	/* if the vm-object is attached to a vm-controller, and the relevant
 	 * page is uncommitted, send a request to the vm-controller to provide
 	 * the missing page. will result in the vm-object being unlocked and
 	 * the current thread sleeping until the request is fulfilled. the
 	 * vm-object will be re-locked before the function returns. */
-	VMO_REQUEST_MISSING_PAGE = 0x08u,
+	VMO_REQUEST_MISSING_PAGE = 0x10u,
 };
 
 struct vm_object {

vm/address-space.c

@@ -7,6 +7,7 @@
 #include <kernel/sched.h>
 #include <kernel/task.h>
 #include <kernel/util.h>
+#include <kernel/vm-controller.h>
 #include <kernel/vm-object.h>
 #include <mango/status.h>
 
@@ -721,6 +722,9 @@ kern_status_t address_space_map(
 	}
 
 	tracek("address_space_map(%zx, %zx)", map_address, length);
+	if (map_address == 0xc6a55000) {
+		printk("break");
+	}
 
 	if (!root || !object) {
 		tracek("null pointer");
@@ -838,7 +842,7 @@ static kern_status_t split_area(
 
 	put_entry(&root->s_mappings, right);
 	for (size_t i = unmap_base; i < unmap_limit; i += VM_PAGE_SIZE) {
-		tracek("unmapping %zx", i);
+		tracek("pmap_remove %zx", i);
 		pmap_remove(root->s_pmap, i);
 	}
 
@@ -875,7 +879,7 @@ static kern_status_t left_reduce_area(
 		return KERN_OK;
 	}
 
-	tracek(" unmapping %zx-%zx (%zx bytes)", base, base + length, length);
+	tracek(" pmap_remove %zx-%zx (%zx bytes)", base, base + length, length);
 	for (size_t i = base; i < limit; i += VM_PAGE_SIZE) {
 		pmap_remove(root->s_pmap, i);
 	}
@@ -912,7 +916,7 @@ static kern_status_t right_reduce_area(
 		return KERN_OK;
 	}
 
-	tracek(" unmapping %zx-%zx (%zx bytes)", base, base + length, length);
+	tracek(" pmap_remove %zx-%zx (%zx bytes)", base, base + length, length);
 	for (size_t i = base; i < limit; i += VM_PAGE_SIZE) {
 		pmap_remove(root->s_pmap, i);
 	}
@@ -930,9 +934,10 @@ static kern_status_t delete_area(
 		return KERN_OK;
 	}
 
-	tracek("delete mapping [%zx-%zx]",
+	tracek("delete mapping [%zx-%zx] (%zx bytes)",
 	       mapping->vma_base,
-	       mapping->vma_limit);
+	       mapping->vma_limit,
+	       mapping->vma_limit - mapping->vma_base);
 
 	for (size_t i = mapping->vma_base; i < mapping->vma_limit;
 	     i += VM_PAGE_SIZE) {
@@ -946,7 +951,23 @@ static kern_status_t delete_area(
 		&mapping->vma_object->vo_mappings,
 		&mapping->vma_object_entry);
 	mapping->vma_object = NULL;
+	/* if the object is attached to a controller and the ref-count is 2,
+	 * then the only other remaining reference to this object is held by
+	 * the controller. */
+	struct vm_controller *ctrl = object->vo_ctrl;
+	bool detach = ctrl != NULL && object->vo_base.ob_refcount == 2
+	           && (object->vo_flags & VMO_AUTO_DETACH);
 	vm_object_unlock_irqrestore(object, flags);
+
+	if (detach) {
+		/* TODO find a better way to achieve this, and/or give the
+		 * server that created the object more control over when it
+		 * should be detached */
+		vm_controller_lock_irqsave(ctrl, &flags);
+		vm_controller_detach_object(ctrl, object);
+		vm_controller_unlock_irqrestore(ctrl, flags);
+	}
+
 	object_unref(&object->vo_base);
 
 	/* don't actually delete the mapping yet. that will be done by

vm/vm-controller.c

@@ -198,7 +198,8 @@ kern_status_t vm_controller_create_object(
 
 	object_ref(&ctrl->vc_base);
 
-	vmo->vo_flags |= VMO_CONTROLLER;
+	/* TODO expose the VMO_AUTO_DETACH flag to userspace */
+	vmo->vo_flags |= VMO_CONTROLLER | VMO_AUTO_DETACH;
 	vmo->vo_ctrl = ctrl;
 	vmo->vo_key = key;