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/*

 * Copyright (C) 2001-2006 Jakub Jermar

 * All rights reserved.

 *

 * Redistribution and use in source and binary forms, with or without

 * modification, are permitted provided that the following conditions

 * are met:

 *

 * - Redistributions of source code must retain the above copyright

 *   notice, this list of conditions and the following disclaimer.

 * - Redistributions in binary form must reproduce the above copyright

 *   notice, this list of conditions and the following disclaimer in the

 *   documentation and/or other materials provided with the distribution.

 * - The name of the author may not be used to endorse or promote products

 *   derived from this software without specific prior written permission.

 *

 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR

 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES

 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.

 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,

 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT

 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,

 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY

 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT

 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF

 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

 */

/**

 * @file	as.c

 * @brief	Address space related functions.

 *

 * This file contains address space manipulation functions.

 * Roughly speaking, this is a higher-level client of

 * Virtual Address Translation (VAT) subsystem.

 *

 * Functionality provided by this file allows one to

 * create address space and create, resize and share

 * address space areas.

 *

 * @see page.c

 *

 */

#include <mm/as.h>

#include <arch/mm/as.h>

#include <mm/page.h>

#include <mm/frame.h>

#include <mm/slab.h>

#include <mm/tlb.h>

#include <arch/mm/page.h>

#include <genarch/mm/page_pt.h>

#include <genarch/mm/page_ht.h>

#include <mm/asid.h>

#include <arch/mm/asid.h>

#include <synch/spinlock.h>

#include <adt/list.h>

#include <adt/btree.h>

#include <proc/task.h>

#include <proc/thread.h>

#include <arch/asm.h>

#include <panic.h>

#include <debug.h>

#include <print.h>

#include <memstr.h>

#include <macros.h>

#include <arch.h>

#include <errno.h>

#include <config.h>

#include <arch/types.h>

#include <typedefs.h>

#include <syscall/copy.h>

#include <arch/interrupt.h>

as_operations_t *as_operations = NULL;

/** Address space lock. It protects inactive_as_with_asid_head. */

SPINLOCK_INITIALIZE(as_lock);

/**

 * This list contains address spaces that are not active on any

 * processor and that have valid ASID.

 */

LIST_INITIALIZE(inactive_as_with_asid_head);

/** Kernel address space. */

as_t *AS_KERNEL = NULL;

static int area_flags_to_page_flags(int aflags);

static int get_area_flags(as_area_t *a);

static as_area_t *find_area_and_lock(as_t *as, __address va);

static bool check_area_conflicts(as_t *as, __address va, size_t size, as_area_t *avoid_area);

/** Initialize address space subsystem. */

void as_init(void)

{

	as_arch_init();

	AS_KERNEL = as_create(FLAG_AS_KERNEL);

        if (!AS_KERNEL)

                panic("can't create kernel address space\n");

}

/** Create address space.

 *

 * @param flags Flags that influence way in wich the address space is created.

 */

as_t *as_create(int flags)

{

	as_t *as;

	as = (as_t *) malloc(sizeof(as_t), 0);

	link_initialize(&as->inactive_as_with_asid_link);

	spinlock_initialize(&as->lock, "as_lock");

	btree_create(&as->as_area_btree);

	if (flags & FLAG_AS_KERNEL)

		as->asid = ASID_KERNEL;

	else

		as->asid = ASID_INVALID;

	as->refcount = 0;

	as->page_table = page_table_create(flags);

	return as;

}

/** Free Adress space */

void as_free(as_t *as)

{

	ASSERT(as->refcount == 0);

	/* TODO: free as_areas and other resources held by as */

	/* TODO: free page table */

	free(as);

}

/** Create address space area of common attributes.

 *

 * The created address space area is added to the target address space.

 *

 * @param as Target address space.

 * @param flags Flags of the area memory.

 * @param size Size of area.

 * @param base Base address of area.

 * @param attrs Attributes of the area.

 *

 * @return Address space area on success or NULL on failure.

 */

as_area_t *as_area_create(as_t *as, int flags, size_t size, __address base, int attrs)

{

	ipl_t ipl;

	as_area_t *a;

	if (base % PAGE_SIZE)

		return NULL;

	if (!size)

		return NULL;

	/* Writeable executable areas are not supported. */

	if ((flags & AS_AREA_EXEC) && (flags & AS_AREA_WRITE))

		return NULL;

	ipl = interrupts_disable();

	spinlock_lock(&as->lock);

	if (!check_area_conflicts(as, base, size, NULL)) {

		spinlock_unlock(&as->lock);

		interrupts_restore(ipl);

		return NULL;

	}

	a = (as_area_t *) malloc(sizeof(as_area_t), 0);

	spinlock_initialize(&a->lock, "as_area_lock");

	a->flags = flags;

	a->attributes = attrs;

	a->pages = SIZE2FRAMES(size);

	a->base = base;

	btree_insert(&as->as_area_btree, base, (void *) a, NULL);

	spinlock_unlock(&as->lock);

	interrupts_restore(ipl);

	return a;

}

/** Find address space area and change it.

 *

 * @param as Address space.

 * @param address Virtual address belonging to the area to be changed. Must be page-aligned.

 * @param size New size of the virtual memory block starting at address. 

 * @param flags Flags influencing the remap operation. Currently unused.

 *

 * @return Zero on success or a value from @ref errno.h otherwise.

 */ 

int as_area_resize(as_t *as, __address address, size_t size, int flags)

{

	as_area_t *area;

	ipl_t ipl;

	size_t pages;

	ipl = interrupts_disable();

	spinlock_lock(&as->lock);

	/*

	 * Locate the area.

	 */

	area = find_area_and_lock(as, address);

	if (!area) {

		spinlock_unlock(&as->lock);

		interrupts_restore(ipl);

		return ENOENT;

	}

	if (area->flags & AS_AREA_DEVICE) {

		/*

		 * Remapping of address space areas associated

		 * with memory mapped devices is not supported.

		 */

		spinlock_unlock(&area->lock);

		spinlock_unlock(&as->lock);

		interrupts_restore(ipl);

		return ENOTSUP;

	}

	pages = SIZE2FRAMES((address - area->base) + size);

	if (!pages) {

		/*

		 * Zero size address space areas are not allowed.

		 */

		spinlock_unlock(&area->lock);

		spinlock_unlock(&as->lock);

		interrupts_restore(ipl);

		return EPERM;

	}

	if (pages < area->pages) {

		int i;

		/*

		 * Shrinking the area.

		 * No need to check for overlaps.

		 */

		for (i = pages; i < area->pages; i++) {

			pte_t *pte;

			/*

			 * Releasing physical memory.

			 * This depends on the fact that the memory was allocated using frame_alloc().

			 */

			page_table_lock(as, false);

			pte = page_mapping_find(as, area->base + i*PAGE_SIZE);

			if (pte && PTE_VALID(pte)) {

				__address frame;

				ASSERT(PTE_PRESENT(pte));

				frame = PTE_GET_FRAME(pte);

				page_mapping_remove(as, area->base + i*PAGE_SIZE);

				page_table_unlock(as, false);

				frame_free(ADDR2PFN(frame));

			} else {

				page_table_unlock(as, false);

			}

		}

		/*

		 * Invalidate TLB's.

		 */

		tlb_shootdown_start(TLB_INVL_PAGES, AS->asid, area->base + pages*PAGE_SIZE, area->pages - pages);

		tlb_invalidate_pages(AS->asid, area->base + pages*PAGE_SIZE, area->pages - pages);

		tlb_shootdown_finalize();

	} else {

		/*

		 * Growing the area.

		 * Check for overlaps with other address space areas.

		 */

		if (!check_area_conflicts(as, address, pages * PAGE_SIZE, area)) {

			spinlock_unlock(&area->lock);

			spinlock_unlock(&as->lock);		

			interrupts_restore(ipl);

			return EADDRNOTAVAIL;

		}

	} 

	area->pages = pages;

	spinlock_unlock(&area->lock);

	spinlock_unlock(&as->lock);

	interrupts_restore(ipl);

	return 0;

}

/** Destroy address space area.

 *

 * @param as Address space.

 * @param address Address withing the area to be deleted.

 *

 * @return Zero on success or a value from @ref errno.h on failure. 

 */

int as_area_destroy(as_t *as, __address address)

{

	as_area_t *area;

	__address base;

	ipl_t ipl;

	int i;

	ipl = interrupts_disable();

	spinlock_lock(&as->lock);

	area = find_area_and_lock(as, address);

	if (!area) {

		spinlock_unlock(&as->lock);

		interrupts_restore(ipl);

		return ENOENT;

	}

	base = area->base;	

	for (i = 0; i < area->pages; i++) {

		pte_t *pte;

		/*

		 * Releasing physical memory.

		 * Areas mapping memory-mapped devices are treated differently than

		 * areas backing frame_alloc()'ed memory.

		 */

		page_table_lock(as, false);

		pte = page_mapping_find(as, area->base + i*PAGE_SIZE);

		if (pte && PTE_VALID(pte)) {

			ASSERT(PTE_PRESENT(pte));

			page_mapping_remove(as, area->base + i*PAGE_SIZE);

			if (area->flags & AS_AREA_DEVICE) {

				__address frame;

				frame = PTE_GET_FRAME(pte);

				frame_free(ADDR2PFN(frame));

			}

			page_table_unlock(as, false);

		} else {

			page_table_unlock(as, false);

		}

	}

	/*

	 * Invalidate TLB's.

	 */

	tlb_shootdown_start(TLB_INVL_PAGES, AS->asid, area->base, area->pages);

	tlb_invalidate_pages(AS->asid, area->base, area->pages);

	tlb_shootdown_finalize();

	area->attributes |= AS_AREA_ATTR_PARTIAL;

	spinlock_unlock(&area->lock);

	/*

	 * Remove the empty area from address space.

	 */

	btree_remove(&AS->as_area_btree, base, NULL);

	free(area);

	spinlock_unlock(&AS->lock);

	interrupts_restore(ipl);

	return 0;

}

/** Send address space area to another task.

 *

 * Address space area is sent to the specified task.

 * If the destination task is willing to accept the

 * area, a new area is created according to the

 * source area. Moreover, any existing mapping

 * is copied as well, providing thus a mechanism

 * for sharing group of pages. The source address

 * space area and any associated mapping is preserved.

 *

 * @param dst_id Task ID of the accepting task.

 * @param src_base Base address of the source address space area.

 *

 * @return Zero on success or ENOENT if there is no such task or

 *	   if there is no such address space area,

 *	   EPERM if there was a problem in accepting the area or

 *	   ENOMEM if there was a problem in allocating destination

 *	   address space area.

 */

int as_area_send(task_id_t dst_id, __address src_base)

{

	ipl_t ipl;

	task_t *t;

	count_t i;

	as_t *dst_as;

	__address dst_base;

	int src_flags;

	size_t src_size;

	as_area_t *src_area, *dst_area;

	ipl = interrupts_disable();

	spinlock_lock(&tasks_lock);

	t = task_find_by_id(dst_id);

	if (!NULL) {

		spinlock_unlock(&tasks_lock);

		interrupts_restore(ipl);

		return ENOENT;

	}

	spinlock_lock(&t->lock);

	spinlock_unlock(&tasks_lock);

	dst_as = t->as;

	dst_base = (__address) t->accept_arg.base;

	if (dst_as == AS) {

		/*

		 * The two tasks share the entire address space.

		 * Return error since there is no point in continuing.

		 */

		spinlock_unlock(&t->lock);

		interrupts_restore(ipl);

		return EPERM;

	}

	spinlock_lock(&AS->lock);

	src_area = find_area_and_lock(AS, src_base);

	if (!src_area) {

		/*

		 * Could not find the source address space area.

		 */

		spinlock_unlock(&t->lock);

		spinlock_unlock(&AS->lock);

		interrupts_restore(ipl);

		return ENOENT;

	}

	src_size = src_area->pages * PAGE_SIZE;

	src_flags = src_area->flags;

	spinlock_unlock(&src_area->lock);

	spinlock_unlock(&AS->lock);

	if ((t->accept_arg.task_id != TASK->taskid) || (t->accept_arg.size != src_size) ||

	    (t->accept_arg.flags != src_flags)) {

		/*

		 * Discrepancy in either task ID, size or flags.

		 */

		spinlock_unlock(&t->lock);

		interrupts_restore(ipl);

		return EPERM;

	}

	/*

	 * Create copy of the source address space area.

	 * The destination area is created with AS_AREA_ATTR_PARTIAL

	 * attribute set which prevents race condition with

	 * preliminary as_page_fault() calls.

	 */

	dst_area = as_area_create(dst_as, src_flags, src_size, dst_base, AS_AREA_ATTR_PARTIAL);

	if (!dst_area) {

		/*

		 * Destination address space area could not be created.

		 */

		spinlock_unlock(&t->lock);

		interrupts_restore(ipl);

		return ENOMEM;

	}

	memsetb((__address) &t->accept_arg, sizeof(as_area_acptsnd_arg_t), 0);

	spinlock_unlock(&t->lock);

	/*

	 * Avoid deadlock by first locking the address space with lower address.

	 */

	if (dst_as < AS) {

		spinlock_lock(&dst_as->lock);

		spinlock_lock(&AS->lock);

	} else {

		spinlock_lock(&AS->lock);

		spinlock_lock(&dst_as->lock);

	}

	for (i = 0; i < SIZE2FRAMES(src_size); i++) {

		pte_t *pte;

		__address frame;

		page_table_lock(AS, false);

		pte = page_mapping_find(AS, src_base + i*PAGE_SIZE);

		if (pte && PTE_VALID(pte)) {

			ASSERT(PTE_PRESENT(pte));

			frame = PTE_GET_FRAME(pte);

			if (!(src_flags & AS_AREA_DEVICE))

				frame_reference_add(ADDR2PFN(frame));

			page_table_unlock(AS, false);

		} else {

			page_table_unlock(AS, false);

			continue;

		}

		page_table_lock(dst_as, false);

		page_mapping_insert(dst_as, dst_base + i*PAGE_SIZE, frame, area_flags_to_page_flags(src_flags));

		page_table_unlock(dst_as, false);

	}

	/*

	 * Now the destination address space area has been

	 * fully initialized. Clear the AS_AREA_ATTR_PARTIAL

	 * attribute.

	 */	

	spinlock_lock(&dst_area->lock);

	dst_area->attributes &= ~AS_AREA_ATTR_PARTIAL;

	spinlock_unlock(&dst_area->lock);

	spinlock_unlock(&AS->lock);

	spinlock_unlock(&dst_as->lock);

	interrupts_restore(ipl);

	return 0;

}

/** Initialize mapping for one page of address space.

 *

 * This functions maps 'page' to 'frame' according

 * to attributes of the address space area to

 * wich 'page' belongs.

 *

 * @param as Target address space.

 * @param page Virtual page within the area.

 * @param frame Physical frame to which page will be mapped.

 */

void as_set_mapping(as_t *as, __address page, __address frame)

{

	as_area_t *area;

	ipl_t ipl;

	ipl = interrupts_disable();

	page_table_lock(as, true);

	area = find_area_and_lock(as, page);

	if (!area) {

		panic("page not part of any as_area\n");

	}

	page_mapping_insert(as, page, frame, get_area_flags(area));

	spinlock_unlock(&area->lock);

	page_table_unlock(as, true);

	interrupts_restore(ipl);

}

/** Handle page fault within the current address space.

 *

 * This is the high-level page fault handler.

 * Interrupts are assumed disabled.

 *

 * @param page Faulting page.

 * @param istate Pointer to interrupted state.

 *

 * @return 0 on page fault, 1 on success or 2 if the fault was caused by copy_to_uspace() or copy_from_uspace().

 */

int as_page_fault(__address page, istate_t *istate)

{

	pte_t *pte;

	as_area_t *area;

	__address frame;

	ASSERT(AS);

	spinlock_lock(&AS->lock);

	area = find_area_and_lock(AS, page);	

	if (!area) {

		/*

		 * No area contained mapping for 'page'.

		 * Signal page fault to low-level handler.

		 */

		spinlock_unlock(&AS->lock);

		goto page_fault;

	}

	if (area->attributes & AS_AREA_ATTR_PARTIAL) {

		/*

		 * The address space area is not fully initialized.

		 * Avoid possible race by returning error.

		 */

		spinlock_unlock(&area->lock);

		spinlock_unlock(&AS->lock);

		goto page_fault;		

	}

	ASSERT(!(area->flags & AS_AREA_DEVICE));

	page_table_lock(AS, false);

	/*

	 * To avoid race condition between two page faults

	 * on the same address, we need to make sure

	 * the mapping has not been already inserted.

	 */

	if ((pte = page_mapping_find(AS, page))) {

		if (PTE_PRESENT(pte)) {

			page_table_unlock(AS, false);

			spinlock_unlock(&area->lock);

			spinlock_unlock(&AS->lock);

			return 1;

		}

	}

	/*

	 * In general, there can be several reasons that

	 * can have caused this fault.

	 *

	 * - non-existent mapping: the area is a scratch

	 *   area (e.g. stack) and so far has not been

	 *   allocated a frame for the faulting page

	 *

	 * - non-present mapping: another possibility,

	 *   currently not implemented, would be frame

	 *   reuse; when this becomes a possibility,

	 *   do not forget to distinguish between

	 *   the different causes

	 */

	frame = PFN2ADDR(frame_alloc(ONE_FRAME, 0));

	memsetb(PA2KA(frame), FRAME_SIZE, 0);

	/*

	 * Map 'page' to 'frame'.

	 * Note that TLB shootdown is not attempted as only new information is being

	 * inserted into page tables.

	 */

	page_mapping_insert(AS, page, frame, get_area_flags(area));

	page_table_unlock(AS, false);

	spinlock_unlock(&area->lock);

	spinlock_unlock(&AS->lock);

	return AS_PF_OK;

page_fault:

	if (!THREAD)

		return AS_PF_FAULT;

	if (THREAD->in_copy_from_uspace) {

		THREAD->in_copy_from_uspace = false;

		istate_set_retaddr(istate, (__address) &memcpy_from_uspace_failover_address);

	} else if (THREAD->in_copy_to_uspace) {

		THREAD->in_copy_to_uspace = false;

		istate_set_retaddr(istate, (__address) &memcpy_to_uspace_failover_address);

	} else {

		return AS_PF_FAULT;

	}

	return AS_PF_DEFER;

}

/** Switch address spaces.

 *

 * @param old Old address space or NULL.

 * @param new New address space.

 */

void as_switch(as_t *old, as_t *new)

{

	ipl_t ipl;

	bool needs_asid = false;

	ipl = interrupts_disable();

	spinlock_lock(&as_lock);

	/*

	 * First, take care of the old address space.

	 */	

	if (old) {

		spinlock_lock(&old->lock);

		ASSERT(old->refcount);

		if((--old->refcount == 0) && (old != AS_KERNEL)) {

			/*

			 * The old address space is no longer active on

			 * any processor. It can be appended to the

			 * list of inactive address spaces with assigned

			 * ASID.

			 */

			 ASSERT(old->asid != ASID_INVALID);

			 list_append(&old->inactive_as_with_asid_link, &inactive_as_with_asid_head);

		}

		spinlock_unlock(&old->lock);

	}

	/*

	 * Second, prepare the new address space.

	 */

	spinlock_lock(&new->lock);

	if ((new->refcount++ == 0) && (new != AS_KERNEL)) {

		if (new->asid != ASID_INVALID)

			list_remove(&new->inactive_as_with_asid_link);

		else

			needs_asid = true;	/* defer call to asid_get() until new->lock is released */

	}

	SET_PTL0_ADDRESS(new->page_table);

	spinlock_unlock(&new->lock);

	if (needs_asid) {

		/*

		 * Allocation of new ASID was deferred

		 * until now in order to avoid deadlock.

		 */

		asid_t asid;

		asid = asid_get();

		spinlock_lock(&new->lock);

		new->asid = asid;

		spinlock_unlock(&new->lock);

	}

	spinlock_unlock(&as_lock);

	interrupts_restore(ipl);

	/*

	 * Perform architecture-specific steps.

	 * (e.g. write ASID to hardware register etc.)

	 */

	as_install_arch(new);

	AS = new;

}

/** Convert address space area flags to page flags.

 *

 * @param aflags Flags of some address space area.

 *

 * @return Flags to be passed to page_mapping_insert().

 */

int area_flags_to_page_flags(int aflags)

{

	int flags;

	flags = PAGE_USER | PAGE_PRESENT;

	if (aflags & AS_AREA_READ)

		flags |= PAGE_READ;

	if (aflags & AS_AREA_WRITE)

		flags |= PAGE_WRITE;

	if (aflags & AS_AREA_EXEC)

		flags |= PAGE_EXEC;

	if (!(aflags & AS_AREA_DEVICE))

		flags |= PAGE_CACHEABLE;

	return flags;

}

/** Compute flags for virtual address translation subsytem.

 *

 * The address space area must be locked.

 * Interrupts must be disabled.

 *

 * @param a Address space area.

 *

 * @return Flags to be used in page_mapping_insert().

 */

int get_area_flags(as_area_t *a)

{

	return area_flags_to_page_flags(a->flags);

}

/** Create page table.

 *

 * Depending on architecture, create either address space

 * private or global page table.

 *

 * @param flags Flags saying whether the page table is for kernel address space.

 *

 * @return First entry of the page table.

 */

pte_t *page_table_create(int flags)

{

        ASSERT(as_operations);

        ASSERT(as_operations->page_table_create);

        return as_operations->page_table_create(flags);

}

/** Lock page table.

 *

 * This function should be called before any page_mapping_insert(),

 * page_mapping_remove() and page_mapping_find().

 * 

 * Locking order is such that address space areas must be locked

 * prior to this call. Address space can be locked prior to this

 * call in which case the lock argument is false.

 *

 * @param as Address space.

 * @param lock If false, do not attempt to lock as->lock.

 */

void page_table_lock(as_t *as, bool lock)

{

	ASSERT(as_operations);

	ASSERT(as_operations->page_table_lock);

	as_operations->page_table_lock(as, lock);

}

/** Unlock page table.

 *

 * @param as Address space.

 * @param unlock If false, do not attempt to unlock as->lock.

 */

void page_table_unlock(as_t *as, bool unlock)

{

	ASSERT(as_operations);

	ASSERT(as_operations->page_table_unlock);

	as_operations->page_table_unlock(as, unlock);

}

/** Find address space area and lock it.

 *

 * The address space must be locked and interrupts must be disabled.

 *

 * @param as Address space.

 * @param va Virtual address.

 *

 * @return Locked address space area containing va on success or NULL on failure.

 */

as_area_t *find_area_and_lock(as_t *as, __address va)

{

	as_area_t *a;

	btree_node_t *leaf, *lnode;

	int i;

	a = (as_area_t *) btree_search(&as->as_area_btree, va, &leaf);

	if (a) {

		/* va is the base address of an address space area */

		spinlock_lock(&a->lock);

		return a;

	}

	/*

	 * Search the leaf node and the righmost record of its left neighbour

	 * to find out whether this is a miss or va belongs to an address

	 * space area found there.

	 */

	/* First, search the leaf node itself. */

	for (i = 0; i < leaf->keys; i++) {

		a = (as_area_t *) leaf->value[i];

		spinlock_lock(&a->lock);

		if ((a->base <= va) && (va < a->base + a->pages * PAGE_SIZE)) {

			return a;

		}

		spinlock_unlock(&a->lock);

	}

	/*

	 * Second, locate the left neighbour and test its last record.

	 * Because of its position in the B+tree, it must have base < va.

	 */

	if ((lnode = btree_leaf_node_left_neighbour(&as->as_area_btree, leaf))) {

		a = (as_area_t *) lnode->value[lnode->keys - 1];

		spinlock_lock(&a->lock);

		if (va < a->base + a->pages * PAGE_SIZE) {

			return a;

		}

		spinlock_unlock(&a->lock);

	}

	return NULL;

}

/** Check area conflicts with other areas.

 *

 * The address space must be locked and interrupts must be disabled.

 *

 * @param as Address space.

 * @param va Starting virtual address of the area being tested.

 * @param size Size of the area being tested.

 * @param avoid_area Do not touch this area. 

 *

 * @return True if there is no conflict, false otherwise.

 */

bool check_area_conflicts(as_t *as, __address va, size_t size, as_area_t *avoid_area)

{

	as_area_t *a;

	btree_node_t *leaf, *node;

	int i;

	/*

	 * We don't want any area to have conflicts with NULL page.

	 */

	if (overlaps(va, size, NULL, PAGE_SIZE))

		return false;

	/*

	 * The leaf node is found in O(log n), where n is proportional to

	 * the number of address space areas belonging to as.

	 * The check for conflicts is then attempted on the rightmost

	 * record in the left neighbour, the leftmost record in the right

	 * neighbour and all records in the leaf node itself.

	 */

	if ((a = (as_area_t *) btree_search(&as->as_area_btree, va, &leaf))) {

		if (a != avoid_area)

			return false;

	}

	/* First, check the two border cases. */

	if ((node = btree_leaf_node_left_neighbour(&as->as_area_btree, leaf))) {

		a = (as_area_t *) node->value[node->keys - 1];

		spinlock_lock(&a->lock);

		if (overlaps(va, size, a->base, a->pages * PAGE_SIZE)) {

			spinlock_unlock(&a->lock);

			return false;

		}

		spinlock_unlock(&a->lock);

	}

	if ((node = btree_leaf_node_right_neighbour(&as->as_area_btree, leaf))) {

		a = (as_area_t *) node->value[0];

		spinlock_lock(&a->lock);

		if (overlaps(va, size, a->base, a->pages * PAGE_SIZE)) {

			spinlock_unlock(&a->lock);

			return false;

		}

		spinlock_unlock(&a->lock);

	}

	/* Second, check the leaf node. */

	for (i = 0; i < leaf->keys; i++) {

		a = (as_area_t *) leaf->value[i];

		if (a == avoid_area)

			continue;

		spinlock_lock(&a->lock);

		if (overlaps(va, size, a->base, a->pages * PAGE_SIZE)) {

			spinlock_unlock(&a->lock);

			return false;

		}

		spinlock_unlock(&a->lock);

	}

	/*

	 * So far, the area does not conflict with other areas.

	 * Check if it doesn't conflict with kernel address space.

	 */	 

	if (!KERNEL_ADDRESS_SPACE_SHADOWED) {

		return !overlaps(va, size, 

			KERNEL_ADDRESS_SPACE_START, KERNEL_ADDRESS_SPACE_END-KERNEL_ADDRESS_SPACE_START);

	}

	return true;

}

/*

 * Address space related syscalls.

 */

/** Wrapper for as_area_create(). */

__native sys_as_area_create(__address address, size_t size, int flags)

{

	if (as_area_create(AS, flags, size, address, AS_AREA_ATTR_NONE))

		return (__native) address;

	else

		return (__native) -1;

}

/** Wrapper for as_area_resize. */

__native sys_as_area_resize(__address address, size_t size, int flags)

{

	return (__native) as_area_resize(AS, address, size, 0);

}

/** Wrapper for as_area_destroy. */

__native sys_as_area_destroy(__address address)

{

	return (__native) as_area_destroy(AS, address);

}

/** Prepare task for accepting address space area from another task.

 *

 * @param uspace_accept_arg Accept structure passed from userspace.

 *

 * @return EPERM if the task ID encapsulated in @uspace_accept_arg references

 *	   TASK. Otherwise zero is returned.

 */

__native sys_as_area_accept(as_area_acptsnd_arg_t *uspace_accept_arg)

{

	as_area_acptsnd_arg_t arg;

	int rc;

	rc = copy_from_uspace(&arg, uspace_accept_arg, sizeof(as_area_acptsnd_arg_t));

	if (rc != 0)

		return rc;

	if (!arg.size)

		return (__native) EPERM;

	if (arg.task_id == TASK->taskid) {

		/*

		 * Accepting from itself is not allowed.

		 */

		return (__native) EPERM;

	}

	memcpy(&TASK->accept_arg, &arg, sizeof(as_area_acptsnd_arg_t));

        return 0;

}

/** Wrapper for as_area_send. */

__native sys_as_area_send(as_area_acptsnd_arg_t *uspace_send_arg)

{

	as_area_acptsnd_arg_t arg;

	int rc;

	rc = copy_from_uspace(&arg, uspace_send_arg, sizeof(as_area_acptsnd_arg_t));

	if (rc != 0)

		return rc;

	if (!arg.size)

		return (__native) EPERM;

	if (arg.task_id == TASK->taskid) {

		/*

		 * Sending to itself is not allowed.

		 */

		return (__native) EPERM;

	}

	return (__native) as_area_send(arg.task_id, (__address) arg.base);

}