syscall: add task_self, task_get_address_space, and vm_region_kill

the rules around acquiring locks have been strictly defined and
implemented, and general lock usage has been improved, to fix and
prevent several different issues.

a vm-region is now destroyed in two separate steps:
 1. it is "killed": all mappings are unmapped and deleted, the
    region is removed from its parent, and the region and all of
    its sub-regions are marked as "dead", preventing any
    further actions from being performed with the region.
 2. it is "destroyed": the vm-region object is de-allocated when
    the last reference/handle is closed. the references that this
    region holds to any sub-regions are also released, meaning
    these regions may also be de-allocated too.

arch/user/hwlock.c

@@ -1,5 +1,5 @@
-#include <kernel/machine/hwlock.h>
 #include <kernel/compiler.h>
+#include <kernel/machine/hwlock.h>
 
 void ml_hwlock_lock(ml_hwlock_t *lck)
 {

arch/x86_64/hwlock.S

@@ -11,6 +11,41 @@ ml_hwlock_lock:
 
 	mov $1, %ecx
 
+	mfence
+
+1:	mov $0, %eax
+	lock cmpxchg %ecx, (%rdi)
+	jne 1b
+
+	pop %rbp
+	ret
+
+
+	.global ml_hwlock_unlock
+	.type ml_hwlock_unlock, @function
+
+	/* %rdi = pointer to ml_hwlock_t (int) */
+ml_hwlock_unlock:
+	push %rbp
+	mov %rsp, %rbp
+
+	movl $0, (%rdi)
+	mfence
+
+	pop %rbp
+	ret
+
+
+	.global ml_hwlock_lock_irq
+	.type ml_hwlock_lock_irq, @function
+
+	/* %rdi = pointer to ml_hwlock_t (int) */
+ml_hwlock_lock_irq:
+	push %rbp
+	mov %rsp, %rbp
+
+	mov $1, %ecx
+
 	cli
 	mfence
 
@@ -21,11 +56,12 @@ ml_hwlock_lock:
 	pop %rbp
 	ret
 
-	.global ml_hwlock_unlock
-	.type ml_hwlock_unlock, @function
+
+	.global ml_hwlock_unlock_irq
+	.type ml_hwlock_unlock_irq, @function
 
 	/* %rdi = pointer to ml_hwlock_t (int) */
-ml_hwlock_unlock:
+ml_hwlock_unlock_irq:
 	push %rbp
 	mov %rsp, %rbp
 
@@ -42,7 +78,7 @@ ml_hwlock_unlock:
 
 	/* %rdi = pointer to ml_hwlock_t (int)
 	   %rsi = pointer to quadword to store rflags in */
-ml_hwlock_lock_irqsave:	
+ml_hwlock_lock_irqsave:
 	push %rbp
 	mov %rsp, %rbp
 
@@ -62,6 +98,7 @@ ml_hwlock_lock_irqsave:
 	pop %rbp
 	ret
 
+
 	.global ml_hwlock_unlock_irqrestore
 	.type ml_hwlock_unlock_irqrestore, @function
 

arch/x86_64/include/arch/msr.h

@@ -3,7 +3,8 @@
 
 #include <stdint.h>
 
-#define MSR_GS_BASE 0xC0000101
+#define MSR_GS_BASE        0xC0000101
+#define MSR_KERNEL_GS_BASE 0xC0000102
 
 #ifdef __cplusplus
 extern "C" {

arch/x86_64/include/kernel/machine/hwlock.h

@@ -12,6 +12,9 @@ typedef int ml_hwlock_t;
 extern void ml_hwlock_lock(ml_hwlock_t *lck);
 extern void ml_hwlock_unlock(ml_hwlock_t *lck);
 
+extern void ml_hwlock_lock_irq(ml_hwlock_t *lck);
+extern void ml_hwlock_unlock_irq(ml_hwlock_t *lck);
+
 extern void ml_hwlock_lock_irqsave(ml_hwlock_t *lck, unsigned long *flags);
 extern void ml_hwlock_unlock_irqrestore(ml_hwlock_t *lck, unsigned long flags);
 

arch/x86_64/irqvec.S

@@ -333,11 +333,30 @@ IRQ 223, 255
 isr_common_stub:
 	PUSH_REGS
 
+	# When ISR occurs in Ring 3, CPU sets %ss (and other non-code selectors)
+	# to 0.
+	mov %ss, %ax
+	cmp $0, %ax
+	jne isr_skipgs1
+
+	mov $0x10, %ax
+	mov %ax, %ss
+	swapgs
+
+isr_skipgs1:
 	mov %rsp, %rdi
 	call isr_dispatch
 
 	POP_REGS
 	add $16, %rsp
+
+	cmpq $0x1b, 32(%rsp)
+	jne isr_skipgs2
+
+	swapgs
+
+isr_skipgs2:
+
 	iretq
 
 
@@ -347,11 +366,31 @@ isr_common_stub:
 irq_common_stub:
 	PUSH_REGS
 
+	# When IRQ occurs in Ring 3, CPU sets %ss (and other non-code selectors)
+	# to 0.
+	mov %ss, %ax
+	cmp $0, %ax
+	jne irq_skipgs1
+
+	mov $0x10, %ax
+	mov %ax, %ss
+	swapgs
+
+irq_skipgs1:
 	mov %rsp, %rdi
 	call irq_dispatch
 
+
 	POP_REGS
 	add $16, %rsp
+
+	cmpq $0x1b, 32(%rsp)
+	jne isr_skipgs2
+
+	swapgs
+
+irq_skipgs2:
+
 	iretq
 
 
@@ -363,12 +402,12 @@ irq_common_stub:
 
 syscall_gate:
 	swapgs
-	movq %rsp, %gs:20       # GS+20 = rsp2 in the current TSS block (user stack storage)
-	movq %gs:4, %rsp	# GS+4  = rsp0 in the current TSS block (per-thread kstack)
+	movq %rsp, %gs:94       # GS+20 = rsp2 in the current TSS block (user stack storage)
+	movq %gs:78, %rsp	# GS+4  = rsp0 in the current TSS block (per-thread kstack)
 
 	# start building a ml_cpu_context
 	pushq $0x1b
-	pushq %gs:20
+	pushq %gs:94
 	push %r11
 	push $0x23
 	push %rcx
@@ -380,10 +419,6 @@ syscall_gate:
 
 	mov %rsp, %rdi
 
-	# switch back to user gs while in syscall_dispatch. Interrupts are enabled in syscall_dispatch,
-	# and if the task gets pre-empted, the incoming task will expect %gs to have its usermode value.
-	swapgs
-
 	call syscall_dispatch
 
 	POP_REGS
@@ -394,8 +429,8 @@ syscall_gate:
 	pop %r11
 	add $16, %rsp
 
-	swapgs
-	movq %gs:20, %rsp       # GS+20 = rsp2 in the current TSS block
+	movq %gs:94, %rsp       # GS+20 = rsp2 in the current TSS block
+
 	swapgs
 
 	# back to usermode

arch/x86_64/pmap.c

@@ -364,7 +364,12 @@ kern_status_t pmap_handle_fault(
 	struct task *task = current_task();
 	struct vm_region *space = task->t_address_space;
 
-	return vm_region_demand_map(space, fault_addr, flags);
+	unsigned long lock_flags;
+	vm_region_lock_irqsave(space, &lock_flags);
+	kern_status_t status = vm_region_demand_map(space, fault_addr, flags);
+	vm_region_unlock_irqrestore(space, lock_flags);
+
+	return status;
 }
 
 kern_status_t pmap_add(

arch/x86_64/thread_switch.S

@@ -73,4 +73,5 @@ ml_thread_switch_user:
 	pop %rax
 
 	add $16, %rsp
+	swapgs
 	iretq

arch/x86_64/tss.c

@@ -1,5 +1,3 @@
-#include "arch/msr.h"
-
 #include <arch/gdt.h>
 #include <arch/tss.h>
 #include <kernel/libc/string.h>
@@ -22,9 +20,6 @@ void tss_init(struct tss *tss, struct tss_ptr *ptr)
 void tss_load(struct tss *tss)
 {
 	tss_flush(TSS_GDT_INDEX);
-
-	uintptr_t kernel_gs_base_reg = 0xC0000102;
-	wrmsr(kernel_gs_base_reg, (uintptr_t)tss);
 }
 
 virt_addr_t tss_get_kstack(struct tss *tss)

include/kernel/locks.h

@@ -10,13 +10,17 @@ extern "C" {
 
 typedef __aligned(8) ml_hwlock_t spin_lock_t;
 
-#define SPIN_LOCK_INIT ML_HWLOCK_INIT
+#define SPIN_LOCK_INIT                ML_HWLOCK_INIT
 
-#define spin_lock(lck) ml_hwlock_lock(lck);
-#define spin_unlock(lck) ml_hwlock_unlock(lck);
+#define spin_lock(lck)                ml_hwlock_lock(lck);
+#define spin_unlock(lck)              ml_hwlock_unlock(lck);
+
+#define spin_lock_irq(lck)            ml_hwlock_lock_irq(lck);
+#define spin_unlock_irq(lck)          ml_hwlock_unlock_irq(lck);
 
 #define spin_lock_irqsave(lck, flags) ml_hwlock_lock_irqsave(lck, flags);
-#define spin_unlock_irqrestore(lck, flags) ml_hwlock_unlock_irqrestore(lck, flags);
+#define spin_unlock_irqrestore(lck, flags)                                     \
+	ml_hwlock_unlock_irqrestore(lck, flags);
 
 #ifdef __cplusplus
 }

include/kernel/object.h

@@ -3,8 +3,8 @@
 
 #include <kernel/flags.h>
 #include <kernel/locks.h>
-#include <mango/status.h>
 #include <kernel/vm.h>
+#include <mango/status.h>
 #include <stddef.h>
 
 #ifdef __cplusplus
@@ -52,7 +52,10 @@ enum object_type_flags {
 };
 
 struct object_ops {
-	kern_status_t (*destroy)(struct object *obj);
+	kern_status_t (*destroy)(struct object *obj, struct queue *q);
+	kern_status_t (*destroy_recurse)(
+		struct queue_entry *entry,
+		struct object **out);
 };
 
 struct object_type {
@@ -67,6 +70,7 @@ struct object_type {
 
 struct object {
 	uint32_t ob_magic;
+	koid_t ob_id;
 	struct object_type *ob_type;
 	spin_lock_t ob_lock;
 	unsigned int ob_refcount;

include/kernel/syscall.h

@@ -24,6 +24,7 @@
 		VM_PROT_READ | VM_PROT_WRITE | VM_PROT_USER)
 
 extern kern_status_t sys_task_exit(int status);
+extern kern_status_t sys_task_self(kern_handle_t *out);
 extern kern_status_t sys_task_create(
 	kern_handle_t parent_handle,
 	const char *name,
@@ -37,6 +38,9 @@ extern kern_status_t sys_task_create_thread(
 	uintptr_t *args,
 	size_t nr_args,
 	kern_handle_t *out_thread);
+extern kern_status_t sys_task_get_address_space(
+	kern_handle_t task,
+	kern_handle_t *out);
 
 extern kern_status_t sys_thread_start(kern_handle_t thread);
 
@@ -75,6 +79,7 @@ extern kern_status_t sys_vm_region_create(
 	vm_prot_t prot,
 	kern_handle_t *out,
 	virt_addr_t *out_base_address);
+extern kern_status_t sys_vm_region_kill(kern_handle_t region);
 extern kern_status_t sys_vm_region_read(
 	kern_handle_t region,
 	void *dst,

include/kernel/vm-region.h

@@ -11,6 +11,11 @@
 struct vm_region;
 struct vm_object;
 
+enum vm_region_status {
+	VM_REGION_DEAD = 0,
+	VM_REGION_ONLINE,
+};
+
 enum vm_region_entry_type {
 	VM_REGION_ENTRY_NONE = 0,
 	VM_REGION_ENTRY_REGION,
@@ -18,9 +23,16 @@ enum vm_region_entry_type {
 };
 
 struct vm_region_entry {
-	struct btree_node e_node;
+	union {
+		struct btree_node e_node;
+		/* this entry is only used to queue vm-region objects for
+		 * recursive cleanup */
+		struct queue_entry e_entry;
+	};
 	struct vm_region_entry *e_parent;
 	enum vm_region_entry_type e_type;
+	/* absolute address of this entry */
+	virt_addr_t e_address;
 	/* offset in bytes of this entry within its immediate parent. */
 	off_t e_offset;
 	/* size of the entry in bytes */
@@ -31,7 +43,7 @@ struct vm_region_mapping {
 	struct vm_region_entry m_entry;
 	struct vm_object *m_object;
 
-	/* used to link to  vm_object->vo_mappings */
+	/* used to link to vm_object->vo_mappings */
 	struct queue_entry m_object_entry;
 
 	vm_prot_t m_prot;
@@ -41,6 +53,7 @@ struct vm_region_mapping {
 
 struct vm_region {
 	struct object vr_base;
+	enum vm_region_status vr_status;
 	struct vm_region_entry vr_entry;
 
 	char vr_name[VM_REGION_NAME_MAX];
@@ -81,6 +94,19 @@ extern kern_status_t vm_region_create(
 	vm_prot_t prot,
 	struct vm_region **out);
 
+/* recursively kills a given region and all of its sub-regions.
+ * when a region is killed, all of its mappings are unmapped, and any further
+ * operations on the region are denied. however, all handles and references to
+ * the region (any any sub-region) remain valid, and no kernel memory is
+ * de-allocated.
+ * the memory used by the vm-region object itself is de-allocated when the last
+ * handle/reference to the object is released.
+ * this function should be called with `region` locked.
+ */
+extern kern_status_t vm_region_kill(
+	struct vm_region *region,
+	unsigned long *lock_flags);
+
 /* map a vm-object into a vm-region.
  * [region_offset,length] must fall within exactly one region, and cannot span
  * multiple sibling regions.

kernel/object.c

@@ -7,6 +7,20 @@
 static struct queue object_types;
 static spin_lock_t object_types_lock = SPIN_LOCK_INIT;
 
+static koid_t koid_alloc(void)
+{
+	static koid_t counter = 0;
+	static spin_lock_t lock = SPIN_LOCK_INIT;
+
+	unsigned long flags;
+	spin_lock_irqsave(&lock, &flags);
+	koid_t result = counter;
+	counter++;
+	spin_unlock_irqrestore(&lock, flags);
+
+	return result;
+}
+
 kern_status_t object_bootstrap(void)
 {
 	return KERN_OK;
@@ -53,6 +67,7 @@ struct object *object_create(struct object_type *type)
 	struct object *obj = (struct object *)((unsigned char *)obj_buf
 	                                       + type->ob_header_offset);
 
+	obj->ob_id = koid_alloc();
 	obj->ob_type = type;
 	obj->ob_lock = SPIN_LOCK_INIT;
 	obj->ob_magic = OBJECT_MAGIC;
@@ -68,6 +83,15 @@ struct object *object_ref(struct object *obj)
 	return obj;
 }
 
+static void __cleanup(struct object *obj, struct queue *queue)
+{
+	if (HAS_OP(obj, destroy)) {
+		obj->ob_type->ob_ops.destroy(obj, queue);
+	}
+
+	vm_cache_free(&obj->ob_type->ob_cache, obj);
+}
+
 static void object_cleanup(struct object *obj, unsigned long flags)
 {
 	if (obj->ob_refcount > 0 || obj->ob_handles > 0) {
@@ -75,11 +99,30 @@ static void object_cleanup(struct object *obj, unsigned long flags)
 		return;
 	}
 
-	if (HAS_OP(obj, destroy)) {
-		obj->ob_type->ob_ops.destroy(obj);
+	struct queue queue = QUEUE_INIT;
+	__cleanup(obj, &queue);
+
+	if (!HAS_OP(obj, destroy_recurse)) {
+		return;
 	}
 
-	vm_cache_free(&obj->ob_type->ob_cache, obj);
+	while (!queue_empty(&queue)) {
+		struct queue_entry *entry = queue_pop_front(&queue);
+		struct object *child = NULL;
+		obj->ob_type->ob_ops.destroy_recurse(entry, &child);
+		if (!child) {
+			continue;
+		}
+
+		if (child->ob_refcount > 1) {
+			child->ob_refcount--;
+			continue;
+		}
+
+		if (child->ob_refcount == 0 && child->ob_handles == 0) {
+			__cleanup(child, &queue);
+		}
+	}
 }
 
 void object_unref(struct object *obj)

libmango/arch/x86_64/syscall.S

@@ -56,8 +56,10 @@
 .endm
 
 SYSCALL_GATE task_exit SYS_TASK_EXIT 1
+SYSCALL_GATE task_self SYS_TASK_SELF 0
 SYSCALL_GATE task_create SYS_TASK_CREATE 5
 SYSCALL_GATE task_create_thread SYS_TASK_CREATE_THREAD 6
+SYSCALL_GATE task_get_address_space SYS_TASK_GET_ADDRESS_SPACE 1
 
 SYSCALL_GATE thread_start SYS_THREAD_START 1
 
@@ -67,6 +69,7 @@ SYSCALL_GATE vm_object_write SYS_VM_OBJECT_WRITE 5
 SYSCALL_GATE vm_object_copy SYS_VM_OBJECT_COPY 6
 
 SYSCALL_GATE vm_region_create SYS_VM_REGION_CREATE 8
+SYSCALL_GATE vm_region_kill SYS_VM_REGION_KILL 1
 SYSCALL_GATE vm_region_read SYS_VM_REGION_READ 5
 SYSCALL_GATE vm_region_write SYS_VM_REGION_WRITE 5
 SYSCALL_GATE vm_region_map_absolute SYS_VM_REGION_MAP_ABSOLUTE 7

libmango/include-user/mango/task.h

@@ -5,6 +5,7 @@
 #include <mango/types.h>
 
 extern kern_status_t task_exit(int status);
+extern kern_status_t task_self(kern_handle_t *out);
 
 extern kern_status_t task_create(
 	kern_handle_t parent,
@@ -19,6 +20,9 @@ extern kern_status_t task_create_thread(
 	uintptr_t *args,
 	size_t nr_args,
 	kern_handle_t *out_thread);
+extern kern_status_t task_get_address_space(
+	kern_handle_t task,
+	kern_handle_t *out);
 
 extern kern_status_t thread_start(kern_handle_t thread);
 

libmango/include-user/mango/vm.h

@@ -39,6 +39,7 @@ extern kern_status_t vm_region_create(
 	vm_prot_t prot,
 	kern_handle_t *out,
 	virt_addr_t *out_base_address);
+extern kern_status_t vm_region_kill(kern_handle_t region);
 extern kern_status_t vm_region_read(
 	kern_handle_t region,
 	void *dst,

libmango/include/mango/syscall.h

@@ -2,14 +2,17 @@
 #define MANGO_SYSCALL_H_
 
 #define SYS_TASK_EXIT                1
+#define SYS_TASK_SELF                31
 #define SYS_TASK_CREATE              2
 #define SYS_TASK_CREATE_THREAD       3
+#define SYS_TASK_GET_ADDRESS_SPACE   33
 #define SYS_THREAD_START             30
 #define SYS_VM_OBJECT_CREATE         4
 #define SYS_VM_OBJECT_READ           5
 #define SYS_VM_OBJECT_WRITE          6
 #define SYS_VM_OBJECT_COPY           29
 #define SYS_VM_REGION_CREATE         7
+#define SYS_VM_REGION_KILL           34
 #define SYS_VM_REGION_READ           8
 #define SYS_VM_REGION_WRITE          9
 #define SYS_VM_REGION_MAP_ABSOLUTE   10

libmango/include/mango/types.h

@@ -45,6 +45,7 @@ typedef uintptr_t phys_addr_t;
 typedef uintptr_t virt_addr_t;
 typedef uint64_t msgid_t;
 typedef uint64_t off_t;
+typedef uint64_t koid_t;
 typedef unsigned int tid_t;
 typedef uint32_t kern_handle_t;
 typedef uint32_t kern_config_key_t;

syscall/dispatch.c

@@ -6,14 +6,17 @@
 
 static const virt_addr_t syscall_table[] = {
 	SYSCALL_TABLE_ENTRY(TASK_EXIT, task_exit),
+	SYSCALL_TABLE_ENTRY(TASK_SELF, task_self),
 	SYSCALL_TABLE_ENTRY(TASK_CREATE, task_create),
 	SYSCALL_TABLE_ENTRY(TASK_CREATE_THREAD, task_create_thread),
+	SYSCALL_TABLE_ENTRY(TASK_GET_ADDRESS_SPACE, task_get_address_space),
 	SYSCALL_TABLE_ENTRY(THREAD_START, thread_start),
 	SYSCALL_TABLE_ENTRY(VM_OBJECT_CREATE, vm_object_create),
 	SYSCALL_TABLE_ENTRY(VM_OBJECT_READ, vm_object_read),
 	SYSCALL_TABLE_ENTRY(VM_OBJECT_WRITE, vm_object_write),
 	SYSCALL_TABLE_ENTRY(VM_OBJECT_COPY, vm_object_copy),
 	SYSCALL_TABLE_ENTRY(VM_REGION_CREATE, vm_region_create),
+	SYSCALL_TABLE_ENTRY(VM_REGION_KILL, vm_region_kill),
 	SYSCALL_TABLE_ENTRY(VM_REGION_READ, vm_region_read),
 	SYSCALL_TABLE_ENTRY(VM_REGION_WRITE, vm_region_write),
 	SYSCALL_TABLE_ENTRY(VM_REGION_MAP_ABSOLUTE, vm_region_map_absolute),

syscall/task.c

@@ -14,6 +14,35 @@ extern kern_status_t sys_task_exit(int status)
 	return KERN_UNIMPLEMENTED;
 }
 
+kern_status_t sys_task_self(kern_handle_t *out)
+{
+	struct task *self = current_task();
+	if (!validate_access_w(self, out, sizeof *out)) {
+		return KERN_MEMORY_FAULT;
+	}
+
+	unsigned long flags;
+	task_lock_irqsave(self, &flags);
+
+	struct handle *handle_slot = NULL;
+	kern_handle_t handle;
+	kern_status_t status = handle_table_alloc_handle(
+		self->t_handles,
+		&handle_slot,
+		&handle);
+	task_unlock_irqrestore(self, flags);
+
+	if (status != KERN_OK) {
+		return status;
+	}
+
+	object_add_handle(&self->t_base);
+	handle_slot->h_object = &self->t_base;
+
+	*out = handle;
+	return KERN_OK;
+}
+
 kern_status_t sys_task_create(
 	kern_handle_t parent_handle,
 	const char *name,
@@ -175,6 +204,57 @@ kern_status_t sys_task_create_thread(
 	return KERN_OK;
 }
 
+kern_status_t sys_task_get_address_space(
+	kern_handle_t task_handle,
+	kern_handle_t *out)
+{
+	struct task *self = current_task();
+	if (!validate_access_w(self, out, sizeof *out)) {
+		return KERN_MEMORY_FAULT;
+	}
+
+	unsigned long flags;
+	task_lock_irqsave(self, &flags);
+
+	struct handle *handle_slot = NULL;
+	kern_handle_t handle;
+	struct object *task_obj = NULL;
+	handle_flags_t handle_flags = 0;
+	kern_status_t status = task_resolve_handle(
+		self,
+		task_handle,
+		&task_obj,
+		&handle_flags);
+	if (status != KERN_OK) {
+		task_unlock_irqrestore(self, flags);
+		return status;
+	}
+
+	status = handle_table_alloc_handle(
+		self->t_handles,
+		&handle_slot,
+		&handle);
+	if (status != KERN_OK) {
+		task_unlock_irqrestore(self, flags);
+		return status;
+	}
+
+	struct task *task = task_cast(task_obj);
+
+	if (!task) {
+		handle_table_free_handle(self->t_handles, handle);
+		task_unlock_irqrestore(self, flags);
+		return KERN_INVALID_ARGUMENT;
+	}
+
+	handle_slot->h_object = &task->t_address_space->vr_base;
+	object_add_handle(&task->t_address_space->vr_base);
+	task_unlock_irqrestore(self, flags);
+
+	*out = handle;
+	return KERN_OK;
+}
+
 kern_status_t sys_thread_start(kern_handle_t thread_handle)
 {
 	unsigned long flags;

syscall/vm-region.c

@@ -63,6 +63,7 @@ kern_status_t sys_vm_region_create(
 
 	object_ref(obj);
 	task_unlock_irqrestore(self, flags);
+	vm_region_lock_irqsave(parent_region, &flags);
 
 	struct vm_region *child = NULL;
 	status = vm_region_create(
@@ -73,6 +74,7 @@ kern_status_t sys_vm_region_create(
 		region_len,
 		prot,
 		&child);
+	vm_region_unlock_irqrestore(parent_region, flags);
 	object_unref(obj);
 
 	if (status != KERN_OK) {
@@ -92,6 +94,39 @@ kern_status_t sys_vm_region_create(
 	return KERN_OK;
 }
 
+kern_status_t sys_vm_region_kill(kern_handle_t region_handle)
+{
+	struct task *self = current_task();
+
+	unsigned long flags;
+	task_lock_irqsave(self, &flags);
+
+	struct object *obj = NULL;
+	handle_flags_t handle_flags = 0;
+	kern_status_t status
+		= task_resolve_handle(self, region_handle, &obj, &handle_flags);
+	if (status != KERN_OK) {
+		task_unlock_irqrestore(self, flags);
+		return status;
+	}
+
+	struct vm_region *region = vm_region_cast(obj);
+	if (!region) {
+		task_unlock_irqrestore(self, flags);
+		return KERN_INVALID_ARGUMENT;
+	}
+
+	object_ref(obj);
+	task_unlock_irqrestore(self, flags);
+
+	vm_region_lock_irqsave(region, &flags);
+	status = vm_region_kill(region, &flags);
+	vm_region_unlock_irqrestore(region, flags);
+	object_unref(obj);
+
+	return status;
+}
+
 kern_status_t sys_vm_region_read(
 	kern_handle_t region_handle,
 	void *dst,

vm/vm-region.c

@@ -8,6 +8,20 @@
 #include <kernel/vm-region.h>
 #include <mango/status.h>
 
+/* NOTE Locking Rules
+ * To avoid deadlocks and crashes, the following locking rules should be
+ * followed:
+ *   1. Do NOT lock more than one region at a time IF the regions are siblings.
+ *   2. When locking a region and it's child(ren) or ancestors, always lock
+ *      the parent region BEFORE the child region.
+ *   3. When locking a region and a vm-object mapped into that region, always
+ *      lock the region BEFORE the vm-object.
+ *   3. An entry MUST be locked before any of its data can be read/written,
+ *      including its children (if it's a region) and its e_parent pointer.
+ *   4. vm_region_mapping has no lock. Instead, its immediate parent region must
+ *      be locked before any child mappings can be accessed.
+ */
+
 /*** STATIC DATA + MACROS *****************************************************/
 
 #undef ASLR
@@ -49,10 +63,21 @@ enum search_direction {
 #define VM_REGION_CAST(p)                                                      \
 	OBJECT_C_CAST(struct vm_region, vr_base, &vm_region_type, p)
 
+static kern_status_t vm_region_object_destroy(struct object *obj);
+
+static kern_status_t region_object_destroy(struct object *obj, struct queue *q);
+static kern_status_t region_object_destroy_recurse(
+	struct queue_entry *entry,
+	struct object **out);
+
 static struct object_type vm_region_type = {
 	.ob_name = "vm-region",
 	.ob_size = sizeof(struct vm_region),
 	.ob_header_offset = offsetof(struct vm_region, vr_base),
+	.ob_ops = {
+		.destroy = region_object_destroy,
+		.destroy_recurse = region_object_destroy_recurse,
+	},
 };
 
 static struct vm_cache mapping_cache = {
@@ -81,17 +106,53 @@ static struct vm_region_mapping *mapping_from_entry(
 	return BTREE_CONTAINER(struct vm_region_mapping, m_entry, entry);
 }
 
-static virt_addr_t entry_absolute_address(const struct vm_region_entry *entry)
+kern_status_t region_object_destroy(struct object *obj, struct queue *q)
 {
-	virt_addr_t result = 0;
-	while (entry) {
-		result += entry->e_offset;
-		entry = entry->e_parent;
+	struct vm_region *region = VM_REGION_CAST(obj);
+	if (region->vr_status == VM_REGION_ONLINE) {
+		panic("last reference closed on an online vm-region");
 	}
 
-	return result;
+	struct btree_node *node = btree_first(&region->vr_entries);
+	while (node) {
+		struct btree_node *next = btree_next(node);
+		btree_delete(&region->vr_entries, node);
+
+		struct vm_region_entry *entry
+			= BTREE_CONTAINER(struct vm_region_entry, e_node, node);
+		if (entry->e_type != VM_REGION_ENTRY_REGION) {
+			panic("offline vm-region still contains non-region "
+			      "children.");
+		}
+
+		queue_push_back(q, &entry->e_entry);
+		node = next;
+	}
+
+	return KERN_OK;
 }
 
+kern_status_t region_object_destroy_recurse(
+	struct queue_entry *entry,
+	struct object **out)
+{
+	struct vm_region_entry *region_entry
+		= BTREE_CONTAINER(struct vm_region_entry, e_entry, entry);
+	if (region_entry->e_type != VM_REGION_ENTRY_REGION) {
+		panic("offline vm-region still contains non-region "
+		      "children.");
+	}
+	struct vm_region *region = region_from_entry(region_entry);
+	*out = &region->vr_base;
+	return KERN_OK;
+}
+
+static virt_addr_t entry_absolute_address(const struct vm_region_entry *entry)
+{
+	return entry->e_address;
+}
+
+/* this function must be called with `parent` locked */
 static void region_put_entry(
 	struct vm_region *parent,
 	struct vm_region_entry *child)
@@ -119,7 +180,15 @@ static void region_put_entry(
 		} else if (child_base > cur_limit) {
 			next = btree_right(cur);
 		} else {
-			panic("tried to add an overlapping entry to vm-region");
+#ifdef TRACE
+			vm_region_dump(parent);
+#endif
+			panic("tried to add an overlapping entry [%zx-%zx] to "
+			      "vm-region (overlaps [%zx-%zx])",
+			      child_base,
+			      child_limit,
+			      cur_base,
+			      cur_limit);
 		}
 
 		if (next) {
@@ -179,12 +248,17 @@ static struct vm_region_entry *region_get_entry(
 
 /* find the child region that covers the area [*offp,len]. searches recursively
  * the value in `offp` is updated to the offset of the returned entry relative
- * to its parent */
+ * to its parent.
+ * this function should be called with `region` locked.
+ * the region returned by this function will also be locked. any intermediary
+ * regions traversed by this function will be locked temporarily, but will
+ * be unlocked by the time the function returns. */
 static struct vm_region *region_get_child_region_recursive(
 	struct vm_region *region,
 	off_t *offp,
 	size_t len)
 {
+	struct vm_region *root = region;
 	off_t offset = *offp;
 	if (offset >= region->vr_entry.e_size) {
 		return NULL;
@@ -197,6 +271,14 @@ static struct vm_region *region_get_child_region_recursive(
 		struct vm_region *next_region = region_from_entry(next);
 		if (next_region) {
 			offset -= next->e_offset;
+			/* since `region` is locked, interrupts are already
+			 * disabled, so don't use lock_irq() here */
+			vm_region_lock(next_region);
+
+			if (region != root) {
+				vm_region_unlock(region);
+			}
+
 			region = next_region;
 		} else {
 			break;
@@ -207,6 +289,12 @@ static struct vm_region *region_get_child_region_recursive(
 	return region;
 }
 
+/* find the vm_region_mapping that contains a given memory area.
+ * `offp` should be a pointer to an off_t value that contains the offset
+ * of the area relative to the start of `region`. this value will be updated
+ * to the offset of the mapping relative to its immediate parent.
+ * this function should be called with `region` locked. if a mapping is found,
+ * it will be returned with its immediate parent locked. */
 static struct vm_region_mapping *region_get_mapping_recursive(
 	struct vm_region *region,
 	off_t *offp,
@@ -218,9 +306,12 @@ static struct vm_region_mapping *region_get_mapping_recursive(
 		return NULL;
 	}
 
+	/* if `region` is a different region than what was originally passed to
+	 * us, it has now been locked, and its children can be accessed. */
 	struct vm_region_entry *entry = region_get_entry(region, offset, len);
 	*offp = offset;
 
+	/* return the mapping with the parent region still locked */
 	return mapping_from_entry(entry);
 }
 
@@ -488,6 +579,7 @@ static kern_status_t region_validate_allocation(
 	return KERN_OK;
 }
 
+/* this function should be called with `region` locked */
 static void vm_iterator_begin(
 	struct vm_iterator *it,
 	struct vm_region *region,
@@ -551,6 +643,15 @@ static void vm_iterator_begin(
 
 static kern_status_t vm_iterator_seek(struct vm_iterator *it, size_t nr_bytes)
 {
+#define UNLOCK_MAPPING_PARENT(p)                                               \
+	do {                                                                   \
+		struct vm_region *parent                                       \
+			= region_from_entry(p->m_entry.e_parent);              \
+		if (parent != it->it_region) {                                 \
+			vm_region_unlock(parent);                              \
+		}                                                              \
+	} while (0)
+
 	if (nr_bytes < it->it_max) {
 		it->it_base += nr_bytes;
 		it->it_buf = (char *)it->it_buf + nr_bytes;
@@ -558,6 +659,10 @@ static kern_status_t vm_iterator_seek(struct vm_iterator *it, size_t nr_bytes)
 		return KERN_OK;
 	}
 
+	/* the parent region of it->it_mapping is locked here. if it is
+	 * different from it->it_region, it must be unlocked */
+	UNLOCK_MAPPING_PARENT(it->it_mapping);
+
 	it->it_base += nr_bytes;
 	off_t offset = it->it_base - vm_region_get_base_address(it->it_region);
 
@@ -569,9 +674,13 @@ static kern_status_t vm_iterator_seek(struct vm_iterator *it, size_t nr_bytes)
 		return KERN_MEMORY_FAULT;
 	}
 
+	/* past this point, if we encounter an error, must remember to unlock
+	 * the parent region of next_mapping */
+
 	if ((next_mapping->m_prot & it->it_prot) != it->it_prot) {
 		it->it_buf = NULL;
 		it->it_max = 0;
+		UNLOCK_MAPPING_PARENT(next_mapping);
 		return KERN_MEMORY_FAULT;
 	}
 
@@ -590,6 +699,7 @@ static kern_status_t vm_iterator_seek(struct vm_iterator *it, size_t nr_bytes)
 	}
 
 	if (!pg) {
+		UNLOCK_MAPPING_PARENT(next_mapping);
 		return KERN_NO_MEMORY;
 	}
 
@@ -620,6 +730,9 @@ static kern_status_t vm_iterator_seek(struct vm_iterator *it, size_t nr_bytes)
 	return KERN_OK;
 }
 
+/* this function must be called with `root` locked. `root` will be the first
+ * entry visited by the iterator. from there, child entries are visited in
+ * depth-first order. */
 static void entry_iterator_begin(
 	struct entry_iterator *it,
 	struct vm_region *root)
@@ -629,8 +742,43 @@ static void entry_iterator_begin(
 	it->it_entry = &root->vr_entry;
 }
 
+/* this function must be called when you are finished with an entry_iterator,
+ * to ensure that all held locks are released. */
+static void entry_iterator_finish(struct entry_iterator *it)
+{
+	struct vm_region_entry *cur = it->it_entry;
+	if (!cur) {
+		return;
+	}
+
+	struct vm_region *region = NULL;
+	if (cur->e_type == VM_REGION_ENTRY_MAPPING) {
+		region = region_from_entry(cur->e_parent);
+	} else {
+		region = region_from_entry(cur);
+	}
+
+	while (region && region != it->it_root) {
+		struct vm_region *parent
+			= region_from_entry(region->vr_entry.e_parent);
+		vm_region_unlock(region);
+		region = parent;
+	}
+
+	memset(it, 0x0, sizeof *it);
+}
+
+/* move to the next entry in the traversal order.
+ * when this function returns:
+ *   1. if the visited entry is a region, it will be locked.
+ *   2. if the visited entry is a mapping, its parent region will be locked.
+ * a region will remain locked until all of its children and n-grand-children
+ * have been visited. once iteration is finished, only `it->it_root` will be
+ * locked.
+ */
 static void entry_iterator_move_next(struct entry_iterator *it)
 {
+	/* `region` is locked */
 	struct vm_region *region = region_from_entry(it->it_entry);
 	bool has_children = (region && !btree_empty(&region->vr_entries));
 
@@ -639,6 +787,15 @@ static void entry_iterator_move_next(struct entry_iterator *it)
 		struct btree_node *node = btree_first(&region->vr_entries);
 		struct vm_region_entry *entry
 			= BTREE_CONTAINER(struct vm_region_entry, e_node, node);
+
+		if (entry->e_type == VM_REGION_ENTRY_REGION) {
+			struct vm_region *child_region
+				= region_from_entry(entry);
+			/* since `region` is locked, interrupts are already
+			 * disabled, so don't use lock_irq() here */
+			vm_region_lock(child_region);
+		}
+
 		it->it_depth++;
 		it->it_entry = entry;
 		return;
@@ -670,6 +827,72 @@ static void entry_iterator_move_next(struct entry_iterator *it)
 			return;
 		}
 
+		if (cur->e_type == VM_REGION_ENTRY_REGION) {
+			struct vm_region *child_region = region_from_entry(cur);
+			if (child_region != it->it_root) {
+				vm_region_unlock(child_region);
+			}
+		}
+
+		it->it_depth--;
+		cur = parent_entry;
+	}
+}
+
+/* erase the current entry and move to the next entry in the traversal order.
+ * the current entry MUST be a mapping, otherwise nothing will happen.
+ */
+static void entry_iterator_erase(struct entry_iterator *it)
+{
+	/* the parent region of `mapping` is locked */
+	struct vm_region_mapping *mapping = mapping_from_entry(it->it_entry);
+	if (!mapping) {
+		return;
+	}
+
+	struct vm_region *parent = region_from_entry(mapping->m_entry.e_parent);
+
+	/* go back up until we find a right sibling. */
+	struct vm_region_entry *cur = it->it_entry;
+
+	while (1) {
+		struct btree_node *sibling = btree_next(&cur->e_node);
+		if (mapping) {
+			btree_delete(
+				&parent->vr_entries,
+				&mapping->m_entry.e_node);
+			vm_cache_free(&mapping_cache, mapping);
+			mapping = NULL;
+		}
+
+		if (sibling) {
+			it->it_entry = BTREE_CONTAINER(
+				struct vm_region_entry,
+				e_node,
+				sibling);
+			return;
+		}
+
+		if (cur == &it->it_root->vr_entry) {
+			it->it_entry = NULL;
+			return;
+		}
+
+		struct vm_region_entry *parent_entry = cur->e_parent;
+		struct vm_region *parent = region_from_entry(parent_entry);
+
+		if (!parent) {
+			it->it_entry = NULL;
+			return;
+		}
+
+		if (cur->e_type == VM_REGION_ENTRY_REGION) {
+			struct vm_region *child_region = region_from_entry(cur);
+			if (child_region != it->it_root) {
+				vm_region_unlock(child_region);
+			}
+		}
+
 		it->it_depth--;
 		cur = parent_entry;
 	}
@@ -705,6 +928,11 @@ static void mapping_iterator_begin(
 	}
 }
 
+static void mapping_iterator_finish(struct entry_iterator *it)
+{
+	entry_iterator_finish(it);
+}
+
 static void mapping_iterator_move_next(
 	struct entry_iterator *it,
 	off_t offset,
@@ -730,6 +958,34 @@ static void mapping_iterator_move_next(
 	}
 }
 
+static void mapping_iterator_erase(
+	struct entry_iterator *it,
+	off_t offset,
+	size_t length,
+	off_t *offp)
+{
+	entry_iterator_erase(it);
+
+	while (it->it_entry
+	       && it->it_entry->e_type != VM_REGION_ENTRY_MAPPING) {
+
+		entry_iterator_move_next(it);
+	}
+
+	if (!it->it_entry) {
+		return;
+	}
+
+	off_t base = entry_absolute_address(it->it_entry)
+	           - it->it_root->vr_entry.e_offset;
+
+	if (base >= offset + length) {
+		it->it_entry = NULL;
+	} else {
+		*offp = base;
+	}
+}
+
 /*** PUBLIC API ***************************************************************/
 
 kern_status_t vm_region_type_init(void)
@@ -743,6 +999,8 @@ struct vm_region *vm_region_cast(struct object *obj)
 	return VM_REGION_CAST(obj);
 }
 
+/* this function should be called with `parent` locked (if parent is non-NULL)
+ */
 kern_status_t vm_region_create(
 	struct vm_region *parent,
 	const char *name,
@@ -752,6 +1010,10 @@ kern_status_t vm_region_create(
 	vm_prot_t prot,
 	struct vm_region **out)
 {
+	if (parent && parent->vr_status != VM_REGION_ONLINE) {
+		return KERN_BAD_STATE;
+	}
+
 	if (!offset || !region_len) {
 		return KERN_INVALID_ARGUMENT;
 	}
@@ -781,8 +1043,10 @@ kern_status_t vm_region_create(
 
 	struct vm_region *region = VM_REGION_CAST(region_object);
 
+	region->vr_status = VM_REGION_ONLINE;
 	region->vr_prot = prot;
 	region->vr_entry.e_type = VM_REGION_ENTRY_REGION;
+	region->vr_entry.e_address = offset;
 	region->vr_entry.e_offset = offset;
 	region->vr_entry.e_size = region_len;
 
@@ -794,8 +1058,11 @@ kern_status_t vm_region_create(
 
 	if (parent) {
 		region->vr_entry.e_parent = &parent->vr_entry;
+		region->vr_entry.e_address += parent->vr_entry.e_address;
 		region->vr_pmap = parent->vr_pmap;
 		region_put_entry(parent, &region->vr_entry);
+		/* `parent` holds a reference to child `region` */
+		object_ref(&region->vr_base);
 	}
 
 	if (name && name_len) {
@@ -808,8 +1075,67 @@ kern_status_t vm_region_create(
 	return KERN_OK;
 }
 
-kern_status_t vm_region_map_object(
+kern_status_t vm_region_kill(
 	struct vm_region *region,
+	unsigned long *lock_flags)
+{
+	if (region->vr_status != VM_REGION_ONLINE) {
+		return KERN_BAD_STATE;
+	}
+
+	if (region->vr_entry.e_parent) {
+		struct vm_region *parent
+			= region_from_entry(region->vr_entry.e_parent);
+		region->vr_entry.e_parent = NULL;
+
+		/* locks must be acquired in parent->child order. since we're
+		 * going backwards here, unlock `region` before locking its
+		 * parent */
+		vm_region_unlock_irqrestore(region, *lock_flags);
+		vm_region_lock_irqsave(parent, lock_flags);
+		btree_delete(&parent->vr_entries, &region->vr_entry.e_node);
+		vm_region_unlock_irqrestore(parent, *lock_flags);
+		vm_region_lock_irqsave(region, lock_flags);
+		/* `region` lock is held, and e_parent is NULL */
+	}
+
+	struct entry_iterator it;
+	entry_iterator_begin(&it, region);
+
+	while (it.it_entry) {
+		if (it.it_entry->e_type == VM_REGION_ENTRY_REGION) {
+			struct vm_region *region
+				= region_from_entry(it.it_entry);
+			region->vr_status = VM_REGION_DEAD;
+			entry_iterator_move_next(&it);
+			continue;
+		}
+
+		struct vm_region_mapping *mapping
+			= mapping_from_entry(it.it_entry);
+
+		virt_addr_t base = entry_absolute_address(it.it_entry);
+
+		for (size_t i = 0; i < mapping->m_entry.e_size;
+		     i += VM_PAGE_SIZE) {
+			pmap_remove(region->vr_pmap, base + i);
+		}
+
+		unsigned long flags;
+		vm_object_lock_irqsave(mapping->m_object, &flags);
+		queue_delete(
+			&mapping->m_object->vo_mappings,
+			&mapping->m_object_entry);
+		vm_object_unlock_irqrestore(mapping->m_object, flags);
+
+		entry_iterator_erase(&it);
+	}
+
+	return KERN_OK;
+}
+
+kern_status_t vm_region_map_object(
+	struct vm_region *root,
 	off_t region_offset,
 	struct vm_object *object,
 	off_t object_offset,
@@ -839,10 +1165,24 @@ kern_status_t vm_region_map_object(
 		length += VM_PAGE_SIZE;
 	}
 
-	if (!region || !object) {
+	if (!root || !object) {
 		return KERN_INVALID_ARGUMENT;
 	}
 
+	struct vm_region *region = root;
+	if (region_offset != VM_REGION_ANY_OFFSET) {
+		region = region_get_child_region_recursive(
+			root,
+			&region_offset,
+			length);
+		/* if `region` != `root`, it will need to be unlocked at the end
+		 * of the function */
+	}
+
+	if (region->vr_status != VM_REGION_ONLINE) {
+		return KERN_BAD_STATE;
+	}
+
 	if ((prot & region->vr_prot) != prot) {
 		return KERN_INVALID_ARGUMENT;
 	}
@@ -855,13 +1195,6 @@ kern_status_t vm_region_map_object(
 		return KERN_INVALID_ARGUMENT;
 	}
 
-	if (region_offset != VM_REGION_ANY_OFFSET) {
-		region = region_get_child_region_recursive(
-			region,
-			&region_offset,
-			length);
-	}
-
 	if (!region) {
 		return KERN_INVALID_ARGUMENT;
 	}
@@ -896,6 +1229,7 @@ kern_status_t vm_region_map_object(
 	mapping->m_object_offset = object_offset;
 	mapping->m_entry.e_type = VM_REGION_ENTRY_MAPPING;
 	mapping->m_entry.e_parent = &region->vr_entry;
+	mapping->m_entry.e_address = region->vr_entry.e_address + region_offset;
 	mapping->m_entry.e_offset = region_offset;
 	mapping->m_entry.e_size = length;
 
@@ -907,7 +1241,14 @@ kern_status_t vm_region_map_object(
 	       abs_base + length);
 #endif
 	region_put_entry(region, &mapping->m_entry);
+	if (region != root) {
+		vm_region_unlock(region);
+	}
+
+	unsigned long lock_flags;
+	vm_object_lock_irqsave(object, &lock_flags);
 	queue_push_back(&object->vo_mappings, &mapping->m_object_entry);
+	vm_object_unlock_irqrestore(object, lock_flags);
 
 	if (out) {
 		*out = entry_absolute_address(&mapping->m_entry);
@@ -1068,12 +1409,13 @@ static kern_status_t delete_mapping(
 		pmap_remove(root->vr_pmap, base + i);
 	}
 
-	struct vm_region *parent = region_from_entry(mapping->m_entry.e_parent);
-
+	unsigned long flags;
+	vm_object_lock_irqsave(mapping->m_object, &flags);
 	queue_delete(&mapping->m_object->vo_mappings, &mapping->m_object_entry);
-	btree_delete(&parent->vr_entries, &mapping->m_entry.e_node);
+	vm_object_unlock_irqrestore(mapping->m_object, flags);
 
-	vm_cache_free(&mapping_cache, mapping);
+	/* don't actually delete the mapping yet. that will be done by
+	 * vm_region_unmap */
 
 	return KERN_OK;
 }
@@ -1083,6 +1425,10 @@ kern_status_t vm_region_unmap(
 	off_t unmap_area_offset,
 	size_t unmap_area_length)
 {
+	if (region->vr_status != VM_REGION_ONLINE) {
+		return KERN_BAD_STATE;
+	}
+
 	kern_status_t status = KERN_OK;
 	struct entry_iterator it;
 	off_t unmap_area_limit = unmap_area_offset + unmap_area_length;
@@ -1101,12 +1447,6 @@ kern_status_t vm_region_unmap(
 		off_t mapping_offset = tmp;
 		off_t mapping_limit = mapping_offset + it.it_entry->e_size;
 
-		mapping_iterator_move_next(
-			&it,
-			unmap_area_offset,
-			unmap_area_length,
-			&tmp);
-
 		bool split
 			= (unmap_area_offset > mapping_offset
 		           && unmap_area_limit < mapping_limit);
@@ -1127,6 +1467,7 @@ kern_status_t vm_region_unmap(
 				mapping_offset,
 				unmap_area_offset,
 				unmap_area_limit);
+			delete = true;
 		} else if (delete) {
 			status = delete_mapping(
 				mapping,
@@ -1150,11 +1491,27 @@ kern_status_t vm_region_unmap(
 			panic("don't know what to do with this mapping");
 		}
 
+		if (delete) {
+			mapping_iterator_erase(
+				&it,
+				unmap_area_offset,
+				unmap_area_length,
+				&tmp);
+		} else {
+			mapping_iterator_move_next(
+				&it,
+				unmap_area_offset,
+				unmap_area_length,
+				&tmp);
+		}
+
 		if (status != KERN_OK) {
 			break;
 		}
 	}
 
+	mapping_iterator_finish(&it);
+
 	return status;
 }
 
@@ -1164,6 +1521,10 @@ bool vm_region_validate_access(
 	size_t len,
 	vm_prot_t prot)
 {
+	if (region->vr_status != VM_REGION_ONLINE) {
+		return false;
+	}
+
 	if (len == 0) {
 		return true;
 	}
@@ -1199,16 +1560,27 @@ bool vm_region_validate_access(
 		if ((mapping->m_prot & prot) != prot) {
 			return false;
 		}
+
+		struct vm_region *parent
+			= region_from_entry(mapping->m_entry.e_parent);
+		if (parent != region) {
+			vm_region_unlock(parent);
+		}
 	}
 
 	return true;
 }
 
+/* this function must be called with `region` locked */
 kern_status_t vm_region_demand_map(
 	struct vm_region *region,
 	virt_addr_t addr,
 	enum pmap_fault_flags flags)
 {
+	if (region->vr_status != VM_REGION_ONLINE) {
+		return KERN_BAD_STATE;
+	}
+
 	addr &= ~VM_PAGE_MASK;
 	if (addr < region->vr_entry.e_offset
 	    || addr > region->vr_entry.e_offset + region->vr_entry.e_size) {
@@ -1230,21 +1602,35 @@ kern_status_t vm_region_demand_map(
 	       mapping->m_object->vo_name,
 	       object_offset);
 
+	unsigned long lock_flags;
+	vm_object_lock_irqsave(mapping->m_object, &lock_flags);
 	struct vm_page *pg = vm_object_alloc_page(
 		mapping->m_object,
 		object_offset,
 		VM_PAGE_4K);
+	vm_object_unlock_irqrestore(mapping->m_object, lock_flags);
 	tracek("vm: mapping %07llx -> %10llx", vm_page_get_paddr(pg), addr);
-	return pmap_add(
+	kern_status_t status = pmap_add(
 		region->vr_pmap,
 		addr,
 		vm_page_get_pfn(pg),
 		mapping->m_prot,
 		PMAP_NORMAL);
+
+	struct vm_region *parent = region_from_entry(mapping->m_entry.e_parent);
+	if (parent != region) {
+		vm_region_unlock(parent);
+	}
+
+	return status;
 }
 
 virt_addr_t vm_region_get_base_address(const struct vm_region *region)
 {
+	if (region->vr_status != VM_REGION_ONLINE) {
+		return 0;
+	}
+
 	return entry_absolute_address(&region->vr_entry);
 }
 
@@ -1255,6 +1641,10 @@ kern_status_t vm_region_read_kernel(
 	void *destp,
 	size_t *nr_read)
 {
+	if (src_region->vr_status != VM_REGION_ONLINE) {
+		return KERN_BAD_STATE;
+	}
+
 	struct vm_iterator src;
 	char *dest = destp;
 
@@ -1296,6 +1686,14 @@ kern_status_t vm_region_memmove(
 	size_t count,
 	size_t *nr_moved)
 {
+	if (src_region->vr_status != VM_REGION_ONLINE) {
+		return KERN_BAD_STATE;
+	}
+
+	if (dest_region->vr_status != VM_REGION_ONLINE) {
+		return KERN_BAD_STATE;
+	}
+
 	struct vm_iterator src, dest;
 	vm_iterator_begin(
 		&src,
@@ -1347,6 +1745,14 @@ extern kern_status_t vm_region_memmove_v(
 	size_t nr_src_vecs,
 	size_t bytes_to_move)
 {
+	if (src_region->vr_status != VM_REGION_ONLINE) {
+		return KERN_BAD_STATE;
+	}
+
+	if (dest_region->vr_status != VM_REGION_ONLINE) {
+		return KERN_BAD_STATE;
+	}
+
 	struct iovec_iterator src, dest;
 	iovec_iterator_begin_user(&src, src_region, src_vecs, nr_src_vecs);
 	iovec_iterator_begin_user(&dest, dest_region, dest_vecs, nr_dest_vecs);