Subversion Repositories HelenOS

/*

 * 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.

 */

/** @addtogroup genericmm

 * @{

 */

/**

 * @file

 * @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 spaces 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 <preemption.h>

#include <synch/spinlock.h>

#include <synch/mutex.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 <align.h>

#include <arch/types.h>

#include <syscall/copy.h>

#include <arch/interrupt.h>

#ifdef CONFIG_VIRT_IDX_DCACHE

#include <arch/mm/cache.h>

#endif /* CONFIG_VIRT_IDX_DCACHE */

#ifndef __OBJC__

/**

 * Each architecture decides what functions will be used to carry out

 * address space operations such as creating or locking page tables.

 */

as_operations_t *as_operations = NULL;

/**

 * Slab for as_t objects.

 */

static slab_cache_t *as_slab;

#endif

/**

 * This lock serializes access to the ASID subsystem.

 * It protects:

 * - inactive_as_with_asid_head list

 * - as->asid for each as of the as_t type

 * - asids_allocated counter

 */

SPINLOCK_INITIALIZE(asidlock);

/**

 * 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 as_area_t *find_area_and_lock(as_t *as, uintptr_t va);

static bool check_area_conflicts(as_t *as, uintptr_t va, size_t size,

    as_area_t *avoid_area);

static void sh_info_remove_reference(share_info_t *sh_info);

#ifndef __OBJC__

static int as_constructor(void *obj, int flags)

{

	as_t *as = (as_t *) obj;

	int rc;

	link_initialize(&as->inactive_as_with_asid_link);

	mutex_initialize(&as->lock);	

	rc = as_constructor_arch(as, flags);

	return rc;

}

static int as_destructor(void *obj)

{

	as_t *as = (as_t *) obj;

	return as_destructor_arch(as);

}

#endif

/** Initialize address space subsystem. */

void as_init(void)

{

	as_arch_init();

#ifndef __OBJC__

	as_slab = slab_cache_create("as_slab", sizeof(as_t), 0,

	    as_constructor, as_destructor, SLAB_CACHE_MAGDEFERRED);

#endif

	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;

#ifdef __OBJC__

	as = [as_t new];

	link_initialize(&as->inactive_as_with_asid_link);

	mutex_initialize(&as->lock);	

	(void) as_constructor_arch(as, flags);

#else

	as = (as_t *) slab_alloc(as_slab, 0);

#endif

	(void) as_create_arch(as, 0);

	btree_create(&as->as_area_btree);

	if (flags & FLAG_AS_KERNEL)

		as->asid = ASID_KERNEL;

	else

		as->asid = ASID_INVALID;

	atomic_set(&as->refcount, 0);

	as->cpu_refcount = 0;

#ifdef AS_PAGE_TABLE

	as->genarch.page_table = page_table_create(flags);

#else

	page_table_create(flags);

#endif

	return as;

}

/** Destroy adress space.

 *

 * When there are no tasks referencing this address space (i.e. its refcount is

 * zero), the address space can be destroyed.

 *

 * We know that we don't hold any spinlock.

 */

void as_destroy(as_t *as)

{

	ipl_t ipl;

	bool cond;

	DEADLOCK_PROBE_INIT(p_asidlock);

	ASSERT(atomic_get(&as->refcount) == 0);

	/*

	 * Since there is no reference to this area,

	 * it is safe not to lock its mutex.

	 */

	/*

	 * We need to avoid deadlock between TLB shootdown and asidlock.

	 * We therefore try to take asid conditionally and if we don't succeed,

	 * we enable interrupts and try again. This is done while preemption is

	 * disabled to prevent nested context switches. We also depend on the

	 * fact that so far no spinlocks are held.

	 */

	preemption_disable();

	ipl = interrupts_read();

retry:

	interrupts_disable();

	if (!spinlock_trylock(&asidlock)) {

		interrupts_enable();

		DEADLOCK_PROBE(p_asidlock, DEADLOCK_THRESHOLD);

		goto retry;

	}

	preemption_enable();	/* Interrupts disabled, enable preemption */

	if (as->asid != ASID_INVALID && as != AS_KERNEL) {

		if (as != AS && as->cpu_refcount == 0)

			list_remove(&as->inactive_as_with_asid_link);

		asid_put(as->asid);

	}

	spinlock_unlock(&asidlock);

	/*

	 * Destroy address space areas of the address space.

	 * The B+tree must be walked carefully because it is

	 * also being destroyed.

	 */	

	for (cond = true; cond; ) {

		btree_node_t *node;

		ASSERT(!list_empty(&as->as_area_btree.leaf_head));

		node = list_get_instance(as->as_area_btree.leaf_head.next,

		    btree_node_t, leaf_link);

		if ((cond = node->keys)) {

			as_area_destroy(as, node->key[0]);

		}

	}

	btree_destroy(&as->as_area_btree);

#ifdef AS_PAGE_TABLE

	page_table_destroy(as->genarch.page_table);

#else

	page_table_destroy(NULL);

#endif

	interrupts_restore(ipl);

#ifdef __OBJC__

	[as free];

#else

	slab_free(as_slab, as);

#endif

}

/** 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.

 * @param backend Address space area backend. NULL if no backend is used.

 * @param backend_data NULL or a pointer to an array holding two void *.

 *

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

 */

as_area_t *

as_area_create(as_t *as, int flags, size_t size, uintptr_t base, int attrs,

	       mem_backend_t *backend, mem_backend_data_t *backend_data)

{

	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();

	mutex_lock(&as->lock);

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

		mutex_unlock(&as->lock);

		interrupts_restore(ipl);

		return NULL;

	}

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

	mutex_initialize(&a->lock);

	a->as = as;

	a->flags = flags;

	a->attributes = attrs;

	a->pages = SIZE2FRAMES(size);

	a->base = base;

	a->sh_info = NULL;

	a->backend = backend;

	if (backend_data)

		a->backend_data = *backend_data;

	else

		memsetb((uintptr_t) &a->backend_data, sizeof(a->backend_data),

		    0);

	btree_create(&a->used_space);

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

	mutex_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, uintptr_t address, size_t size, int flags)

{

	as_area_t *area;

	ipl_t ipl;

	size_t pages;

	ipl = interrupts_disable();

	mutex_lock(&as->lock);

	/*

	 * Locate the area.

	 */

	area = find_area_and_lock(as, address);

	if (!area) {

		mutex_unlock(&as->lock);

		interrupts_restore(ipl);

		return ENOENT;

	}

	if (area->backend == &phys_backend) {

		/*

		 * Remapping of address space areas associated

		 * with memory mapped devices is not supported.

		 */

		mutex_unlock(&area->lock);

		mutex_unlock(&as->lock);

		interrupts_restore(ipl);

		return ENOTSUP;

	}

	if (area->sh_info) {

		/*

		 * Remapping of shared address space areas 

		 * is not supported.

		 */

		mutex_unlock(&area->lock);

		mutex_unlock(&as->lock);

		interrupts_restore(ipl);

		return ENOTSUP;

	}

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

	if (!pages) {

		/*

		 * Zero size address space areas are not allowed.

		 */

		mutex_unlock(&area->lock);

		mutex_unlock(&as->lock);

		interrupts_restore(ipl);

		return EPERM;

	}

	if (pages < area->pages) {

		bool cond;

		uintptr_t start_free = area->base + pages*PAGE_SIZE;

		/*

		 * Shrinking the area.

		 * No need to check for overlaps.

		 */

		/*

		 * Start TLB shootdown sequence.

		 */

		tlb_shootdown_start(TLB_INVL_PAGES, AS->asid, area->base +

		    pages * PAGE_SIZE, area->pages - pages);

		/*

		 * Remove frames belonging to used space starting from

		 * the highest addresses downwards until an overlap with

		 * the resized address space area is found. Note that this

		 * is also the right way to remove part of the used_space

		 * B+tree leaf list.

		 */		

		for (cond = true; cond;) {

			btree_node_t *node;

			ASSERT(!list_empty(&area->used_space.leaf_head));

			node = 

			    list_get_instance(area->used_space.leaf_head.prev,

			    btree_node_t, leaf_link);

			if ((cond = (bool) node->keys)) {

				uintptr_t b = node->key[node->keys - 1];

				count_t c =

				    (count_t) node->value[node->keys - 1];

				unsigned int i = 0;

				if (overlaps(b, c * PAGE_SIZE, area->base,

				    pages * PAGE_SIZE)) {

					if (b + c * PAGE_SIZE <= start_free) {

						/*

						 * The whole interval fits

						 * completely in the resized

						 * address space area.

						 */

						break;

					}

					/*

					 * Part of the interval corresponding

					 * to b and c overlaps with the resized

					 * address space area.

					 */

					cond = false;	/* we are almost done */

					i = (start_free - b) >> PAGE_WIDTH;

					if (!used_space_remove(area, start_free, c - i))

						panic("Could not remove used space.\n");

				} else {

					/*

					 * The interval of used space can be

					 * completely removed.

					 */

					if (!used_space_remove(area, b, c))

						panic("Could not remove used space.\n");

				}

				for (; i < c; i++) {

					pte_t *pte;

					page_table_lock(as, false);

					pte = page_mapping_find(as, b +

					    i * PAGE_SIZE);

					ASSERT(pte && PTE_VALID(pte) &&

					    PTE_PRESENT(pte));

					if (area->backend &&

					    area->backend->frame_free) {

						area->backend->frame_free(area,

						    b + i * PAGE_SIZE,

						    PTE_GET_FRAME(pte));

					}

					page_mapping_remove(as, b +

					    i * PAGE_SIZE);

					page_table_unlock(as, false);

				}

			}

		}

		/*

		 * Finish TLB shootdown sequence.

		 */

		tlb_invalidate_pages(as->asid, area->base + pages * PAGE_SIZE,

		    area->pages - pages);

		/*

		 * Invalidate software translation caches (e.g. TSB on sparc64).

		 */

		as_invalidate_translation_cache(as, 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)) {

			mutex_unlock(&area->lock);

			mutex_unlock(&as->lock);		

			interrupts_restore(ipl);

			return EADDRNOTAVAIL;

		}

	} 

	area->pages = pages;

	mutex_unlock(&area->lock);

	mutex_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, uintptr_t address)

{

	as_area_t *area;

	uintptr_t base;

	link_t *cur;

	ipl_t ipl;

	ipl = interrupts_disable();

	mutex_lock(&as->lock);

	area = find_area_and_lock(as, address);

	if (!area) {

		mutex_unlock(&as->lock);

		interrupts_restore(ipl);

		return ENOENT;

	}

	base = area->base;

	/*

	 * Start TLB shootdown sequence.

	 */

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

	/*

	 * Visit only the pages mapped by used_space B+tree.

	 */

	for (cur = area->used_space.leaf_head.next;

	    cur != &area->used_space.leaf_head; cur = cur->next) {

		btree_node_t *node;

		unsigned int i;

		node = list_get_instance(cur, btree_node_t, leaf_link);

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

			uintptr_t b = node->key[i];

			count_t j;

			pte_t *pte;

			for (j = 0; j < (count_t) node->value[i]; j++) {

				page_table_lock(as, false);

				pte = page_mapping_find(as, b + j * PAGE_SIZE);

				ASSERT(pte && PTE_VALID(pte) &&

				    PTE_PRESENT(pte));

				if (area->backend &&

				    area->backend->frame_free) {

					area->backend->frame_free(area,	b +

					    j * PAGE_SIZE, PTE_GET_FRAME(pte));

				}

				page_mapping_remove(as, b + j * PAGE_SIZE);				

				page_table_unlock(as, false);

			}

		}

	}

	/*

	 * Finish TLB shootdown sequence.

	 */

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

	/*

	 * Invalidate potential software translation caches (e.g. TSB on

	 * sparc64).

	 */

	as_invalidate_translation_cache(as, area->base, area->pages);

	tlb_shootdown_finalize();

	btree_destroy(&area->used_space);

	area->attributes |= AS_AREA_ATTR_PARTIAL;

	if (area->sh_info)

		sh_info_remove_reference(area->sh_info);

	mutex_unlock(&area->lock);

	/*

	 * Remove the empty area from address space.

	 */

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

	free(area);

	mutex_unlock(&as->lock);

	interrupts_restore(ipl);

	return 0;

}

/** Share address space area with another or the same address space.

 *

 * Address space area mapping is shared with a new address space area.

 * If the source address space area has not been shared so far,

 * a new sh_info is created. The new address space area simply gets the

 * sh_info of the source area. The process of duplicating the

 * mapping is done through the backend share function.

 * 

 * @param src_as Pointer to source address space.

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

 * @param acc_size Expected size of the source area.

 * @param dst_as Pointer to destination address space.

 * @param dst_base Target base address.

 * @param dst_flags_mask Destination address space area flags mask.

 *

 * @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. ENOTSUP is returned if the address space area backend does not support

 * sharing.

 */

int as_area_share(as_t *src_as, uintptr_t src_base, size_t acc_size,

    as_t *dst_as, uintptr_t dst_base, int dst_flags_mask)

{

	ipl_t ipl;

	int src_flags;

	size_t src_size;

	as_area_t *src_area, *dst_area;

	share_info_t *sh_info;

	mem_backend_t *src_backend;

	mem_backend_data_t src_backend_data;

	ipl = interrupts_disable();

	mutex_lock(&src_as->lock);

	src_area = find_area_and_lock(src_as, src_base);

	if (!src_area) {

		/*

		 * Could not find the source address space area.

		 */

		mutex_unlock(&src_as->lock);

		interrupts_restore(ipl);

		return ENOENT;

	}

	if (!src_area->backend || !src_area->backend->share) {

		/*

		 * There is no backend or the backend does not

		 * know how to share the area.

		 */

		mutex_unlock(&src_area->lock);

		mutex_unlock(&src_as->lock);

		interrupts_restore(ipl);

		return ENOTSUP;

	}

	src_size = src_area->pages * PAGE_SIZE;

	src_flags = src_area->flags;

	src_backend = src_area->backend;

	src_backend_data = src_area->backend_data;

	/* Share the cacheable flag from the original mapping */

	if (src_flags & AS_AREA_CACHEABLE)

		dst_flags_mask |= AS_AREA_CACHEABLE;

	if (src_size != acc_size ||

	    (src_flags & dst_flags_mask) != dst_flags_mask) {

		mutex_unlock(&src_area->lock);

		mutex_unlock(&src_as->lock);

		interrupts_restore(ipl);

		return EPERM;

	}

	/*

	 * Now we are committed to sharing the area.

	 * First, prepare the area for sharing.

	 * Then it will be safe to unlock it.

	 */

	sh_info = src_area->sh_info;

	if (!sh_info) {

		sh_info = (share_info_t *) malloc(sizeof(share_info_t), 0);

		mutex_initialize(&sh_info->lock);

		sh_info->refcount = 2;

		btree_create(&sh_info->pagemap);

		src_area->sh_info = sh_info;

		/*

		 * Call the backend to setup sharing.

		 */

		src_area->backend->share(src_area);

	} else {

		mutex_lock(&sh_info->lock);

		sh_info->refcount++;

		mutex_unlock(&sh_info->lock);

	}

	mutex_unlock(&src_area->lock);

	mutex_unlock(&src_as->lock);

	/*

	 * 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.

	 * The flags of the source area are masked against dst_flags_mask

	 * to support sharing in less privileged mode.

	 */

	dst_area = as_area_create(dst_as, dst_flags_mask, src_size, dst_base,

	    AS_AREA_ATTR_PARTIAL, src_backend, &src_backend_data);

	if (!dst_area) {

		/*

		 * Destination address space area could not be created.

		 */

		sh_info_remove_reference(sh_info);

		interrupts_restore(ipl);

		return ENOMEM;

	}

	/*

	 * Now the destination address space area has been

	 * fully initialized. Clear the AS_AREA_ATTR_PARTIAL

	 * attribute and set the sh_info.

	 */	

	mutex_lock(&dst_as->lock);	

	mutex_lock(&dst_area->lock);

	dst_area->attributes &= ~AS_AREA_ATTR_PARTIAL;

	dst_area->sh_info = sh_info;

	mutex_unlock(&dst_area->lock);

	mutex_unlock(&dst_as->lock);	

	interrupts_restore(ipl);

	return 0;

}

/** Check access mode for address space area.

 *

 * The address space area must be locked prior to this call.

 *

 * @param area Address space area.

 * @param access Access mode.

 *

 * @return False if access violates area's permissions, true otherwise.

 */

bool as_area_check_access(as_area_t *area, pf_access_t access)

{

	int flagmap[] = {

		[PF_ACCESS_READ] = AS_AREA_READ,

		[PF_ACCESS_WRITE] = AS_AREA_WRITE,

		[PF_ACCESS_EXEC] = AS_AREA_EXEC

	};

	if (!(area->flags & flagmap[access]))

		return false;

	return true;

}

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

 *

 * This is the high-level page fault handler. It decides

 * whether the page fault can be resolved by any backend

 * and if so, it invokes the backend to resolve the page

 * fault.

 *

 * Interrupts are assumed disabled.

 *

 * @param page Faulting page.

 * @param access Access mode that caused the fault (i.e. read/write/exec).

 * @param istate Pointer to interrupted state.

 *

 * @return AS_PF_FAULT on page fault, AS_PF_OK on success or AS_PF_DEFER if the

 * 	   fault was caused by copy_to_uspace() or copy_from_uspace().

 */

int as_page_fault(uintptr_t page, pf_access_t access, istate_t *istate)

{

	pte_t *pte;

	as_area_t *area;

	if (!THREAD)

		return AS_PF_FAULT;

	ASSERT(AS);

	mutex_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.

		 */

		mutex_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.

		 */

		mutex_unlock(&area->lock);

		mutex_unlock(&AS->lock);

		goto page_fault;		

	}

	if (!area->backend || !area->backend->page_fault) {

		/*

		 * The address space area is not backed by any backend

		 * or the backend cannot handle page faults.

		 */

		mutex_unlock(&area->lock);

		mutex_unlock(&AS->lock);

		goto page_fault;		

	}

	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)) {

			if (((access == PF_ACCESS_READ) && PTE_READABLE(pte)) ||

			    (access == PF_ACCESS_WRITE && PTE_WRITABLE(pte)) ||

			    (access == PF_ACCESS_EXEC && PTE_EXECUTABLE(pte))) {

				page_table_unlock(AS, false);

				mutex_unlock(&area->lock);

				mutex_unlock(&AS->lock);

				return AS_PF_OK;

			}

		}

	}

	/*

	 * Resort to the backend page fault handler.

	 */

	if (area->backend->page_fault(area, page, access) != AS_PF_OK) {

		page_table_unlock(AS, false);

		mutex_unlock(&area->lock);

		mutex_unlock(&AS->lock);

		goto page_fault;

	}

	page_table_unlock(AS, false);

	mutex_unlock(&area->lock);

	mutex_unlock(&AS->lock);

	return AS_PF_OK;

page_fault:

	if (THREAD->in_copy_from_uspace) {

		THREAD->in_copy_from_uspace = false;

		istate_set_retaddr(istate,

		    (uintptr_t) &memcpy_from_uspace_failover_address);

	} else if (THREAD->in_copy_to_uspace) {

		THREAD->in_copy_to_uspace = false;

		istate_set_retaddr(istate,

		    (uintptr_t) &memcpy_to_uspace_failover_address);

	} else {

		return AS_PF_FAULT;

	}

	return AS_PF_DEFER;

}

/** Switch address spaces.

 *

 * Note that this function cannot sleep as it is essentially a part of

 * scheduling. Sleeping here would lead to deadlock on wakeup. Another

 * thing which is forbidden in this context is locking the address space.

 *

 * When this function is enetered, no spinlocks may be held.

 *

 * @param old Old address space or NULL.

 * @param new New address space.

 */

void as_switch(as_t *old_as, as_t *new_as)

{

	DEADLOCK_PROBE_INIT(p_asidlock);

	preemption_disable();

retry:

	(void) interrupts_disable();

	if (!spinlock_trylock(&asidlock)) {

		/* 

		 * Avoid deadlock with TLB shootdown.

		 * We can enable interrupts here because

		 * preemption is disabled. We should not be

		 * holding any other lock.

		 */

		(void) interrupts_enable();

		DEADLOCK_PROBE(p_asidlock, DEADLOCK_THRESHOLD);

		goto retry;

	}

	preemption_enable();

	/*

	 * First, take care of the old address space.

	 */	

	if (old_as) {

		ASSERT(old_as->cpu_refcount);

		if((--old_as->cpu_refcount == 0) && (old_as != 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_as->asid != ASID_INVALID);

			list_append(&old_as->inactive_as_with_asid_link,

			    &inactive_as_with_asid_head);

		}

		/*

		 * Perform architecture-specific tasks when the address space

		 * is being removed from the CPU.

		 */

		as_deinstall_arch(old_as);

	}

	/*

	 * Second, prepare the new address space.

	 */

	if ((new_as->cpu_refcount++ == 0) && (new_as != AS_KERNEL)) {

		if (new_as->asid != ASID_INVALID)

			list_remove(&new_as->inactive_as_with_asid_link);

		else

			new_as->asid = asid_get();

	}

#ifdef AS_PAGE_TABLE

	SET_PTL0_ADDRESS(new_as->genarch.page_table);

#endif

	/*

	 * Perform architecture-specific steps.

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

	 */

	as_install_arch(new_as);

	spinlock_unlock(&asidlock);

	AS = new_as;

}

/** 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_CACHEABLE)

		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 as_area_get_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)

{

#ifdef __OBJC__

	return [as_t page_table_create: flags];

#else

	ASSERT(as_operations);

	ASSERT(as_operations->page_table_create);

	return as_operations->page_table_create(flags);

#endif

}

/** Destroy page table.

 *

 * Destroy page table in architecture specific way.

 *

 * @param page_table Physical address of PTL0.

 */

void page_table_destroy(pte_t *page_table)

{

#ifdef __OBJC__

	return [as_t page_table_destroy: page_table];

#else

	ASSERT(as_operations);

	ASSERT(as_operations->page_table_destroy);

	as_operations->page_table_destroy(page_table);

#endif

}

/** 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)

{

#ifdef __OBJC__

	[as page_table_lock: lock];

#else

	ASSERT(as_operations);

	ASSERT(as_operations->page_table_lock);