as.c

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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.
 */

#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 <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 <typedefs.h>
#include <syscall/copy.h>
#include <arch/interrupt.h>

as_operations_t *as_operations = NULL;

SPINLOCK_INITIALIZE(inactive_as_with_asid_lock);

LIST_INITIALIZE(inactive_as_with_asid_head);

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

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");
        
}

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);
        mutex_initialize(&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->cpu_refcount = 0;
        as->page_table = page_table_create(flags);

        return as;
}

void as_destroy(as_t *as)
{
        ipl_t ipl;
        bool cond;

        ASSERT(as->refcount == 0);
        
        /*
         * Since there is no reference to this area,
         * it is safe not to lock its mutex.
         */
        ipl = interrupts_disable();
        spinlock_lock(&inactive_as_with_asid_lock);
        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(&inactive_as_with_asid_lock);

        /*
         * Destroy address space areas of the address space.
         * The B+tee 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);
        page_table_destroy(as->page_table);

        interrupts_restore(ipl);
        
        free(as);
}

as_area_t *as_area_create(as_t *as, int flags, size_t size, __address 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((__address) &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;
}

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();
        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;
                __address 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)) {
                                __address b = node->key[node->keys - 1];
                                count_t c = (count_t) node->value[node->keys - 1];
                                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.");
                                } 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);
                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;
}

int as_area_destroy(as_t *as, __address address)
{
        as_area_t *area;
        __address 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;
                int i;
                
                node = list_get_instance(cur, btree_node_t, leaf_link);
                for (i = 0; i < node->keys; i++) {
                        __address 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);
        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;
}

int as_area_share(as_t *src_as, __address src_base, size_t acc_size,
                  as_t *dst_as, __address 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 now 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;
        } else {
                mutex_lock(&sh_info->lock);
                sh_info->refcount++;
                mutex_unlock(&sh_info->lock);
        }

        src_area->backend->share(src_area);

        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_area->lock);
        dst_area->attributes &= ~AS_AREA_ATTR_PARTIAL;
        dst_area->sh_info = sh_info;
        mutex_unlock(&dst_area->lock);
        
        interrupts_restore(ipl);
        
        return 0;
}

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;
}

int as_page_fault(__address 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, (__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;
}

void as_switch(as_t *old, as_t *new)
{
        ipl_t ipl;
        bool needs_asid = false;
        
        ipl = interrupts_disable();
        spinlock_lock(&inactive_as_with_asid_lock);

        /*
         * First, take care of the old address space.
         */     
        if (old) {
                mutex_lock_active(&old->lock);
                ASSERT(old->cpu_refcount);
                if((--old->cpu_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);
                }
                mutex_unlock(&old->lock);
        }

        /*
         * Second, prepare the new address space.
         */
        mutex_lock_active(&new->lock);
        if ((new->cpu_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);
        mutex_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();
                mutex_lock_active(&new->lock);
                new->asid = asid;
                mutex_unlock(&new->lock);
        }
        spinlock_unlock(&inactive_as_with_asid_lock);
        interrupts_restore(ipl);
        
        /*
         * Perform architecture-specific steps.
         * (e.g. write ASID to hardware register etc.)
         */
        as_install_arch(new);
        
        AS = new;
}

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;
}

int as_area_get_flags(as_area_t *a)
{
        return area_flags_to_page_flags(a->flags);
}

pte_t *page_table_create(int flags)
{
        ASSERT(as_operations);
        ASSERT(as_operations->page_table_create);

        return as_operations->page_table_create(flags);
}

void page_table_destroy(pte_t *page_table)
{
        ASSERT(as_operations);
        ASSERT(as_operations->page_table_destroy);

        as_operations->page_table_destroy(page_table);
}

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);
}

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);
}


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 */
                mutex_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];
                mutex_lock(&a->lock);
                if ((a->base <= va) && (va < a->base + a->pages * PAGE_SIZE)) {
                        return a;
                }
                mutex_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];
                mutex_lock(&a->lock);
                if (va < a->base + a->pages * PAGE_SIZE) {
                        return a;
                }
                mutex_unlock(&a->lock);
        }

        return NULL;
}

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];
                mutex_lock(&a->lock);
                if (overlaps(va, size, a->base, a->pages * PAGE_SIZE)) {
                        mutex_unlock(&a->lock);
                        return false;
                }
                mutex_unlock(&a->lock);
        }
        if ((node = btree_leaf_node_right_neighbour(&as->as_area_btree, leaf))) {
                a = (as_area_t *) node->value[0];
                mutex_lock(&a->lock);
                if (overlaps(va, size, a->base, a->pages * PAGE_SIZE)) {
                        mutex_unlock(&a->lock);
                        return false;
                }
                mutex_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;
        
                mutex_lock(&a->lock);
                if (overlaps(va, size, a->base, a->pages * PAGE_SIZE)) {
                        mutex_unlock(&a->lock);
                        return false;
                }
                mutex_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;
}

size_t as_get_size(__address base)
{
        ipl_t ipl;
        as_area_t *src_area;
        size_t size;

        ipl = interrupts_disable();
        src_area = find_area_and_lock(AS, base);
        if (src_area){
                size = src_area->pages * PAGE_SIZE;
                mutex_unlock(&src_area->lock);
        } else {
                size = 0;
        }
        interrupts_restore(ipl);
        return size;
}

int used_space_insert(as_area_t *a, __address page, count_t count)
{
        btree_node_t *leaf, *node;
        count_t pages;
        int i;

        ASSERT(page == ALIGN_DOWN(page, PAGE_SIZE));
        ASSERT(count);

        pages = (count_t) btree_search(&a->used_space, page, &leaf);
        if (pages) {
                /*
                 * We hit the beginning of some used space.
                 */
                return 0;
        }

        if (!leaf->keys) {
                btree_insert(&a->used_space, page, (void *) count, leaf);
                return 1;
        }

        node = btree_leaf_node_left_neighbour(&a->used_space, leaf);
        if (node) {
                __address left_pg = node->key[node->keys - 1], right_pg = leaf->key[0];
                count_t left_cnt = (count_t) node->value[node->keys - 1], right_cnt = (count_t) leaf->value[0];
                
                /*
                 * Examine the possibility that the interval fits
                 * somewhere between the rightmost interval of
                 * the left neigbour and the first interval of the leaf.
                 */
                 
                if (page >= right_pg) {
                        /* Do nothing. */
                } else if (overlaps(page, count*PAGE_SIZE, left_pg, left_cnt*PAGE_SIZE)) {
                        /* The interval intersects with the left interval. */
                        return 0;
                } else if (overlaps(page, count*PAGE_SIZE, right_pg, right_cnt*PAGE_SIZE)) {
                        /* The interval intersects with the right interval. */
                        return 0;                       
                } else if ((page == left_pg + left_cnt*PAGE_SIZE) && (page + count*PAGE_SIZE == right_pg)) {
                        /* The interval can be added by merging the two already present intervals. */
                        node->value[node->keys - 1] += count + right_cnt;
                        btree_remove(&a->used_space, right_pg, leaf);
                        return 1; 
                } else if (page == left_pg + left_cnt*PAGE_SIZE) {
                        /* The interval can be added by simply growing the left interval. */
                        node->value[node->keys - 1] += count;
                        return 1;
                } else if (page + count*PAGE_SIZE == right_pg) {
                        /*
                         * The interval can be addded by simply moving base of the right
                         * interval down and increasing its size accordingly.
                         */
                        leaf->value[0] += count;
                        leaf->key[0] = page;
                        return 1;
                } else {
                        /*
                         * The interval is between both neigbouring intervals,
                         * but cannot be merged with any of them.
                         */
                        btree_insert(&a->used_space, page, (void *) count, leaf);
                        return 1;
                }
        } else if (page < leaf->key[0]) {
                __address right_pg = leaf->key[0];
                count_t right_cnt = (count_t) leaf->value[0];
        
                /*
                 * Investigate the border case in which the left neighbour does not
                 * exist but the interval fits from the left.
                 */
                 
                if (overlaps(page, count*PAGE_SIZE, right_pg, right_cnt*PAGE_SIZE)) {
                        /* The interval intersects with the right interval. */
                        return 0;
                } else if (page + count*PAGE_SIZE == right_pg) {
                        /*
                         * The interval can be added by moving the base of the right interval down
                         * and increasing its size accordingly.
                         */
                        leaf->key[0] = page;
                        leaf->value[0] += count;
                        return 1;
                } else {
                        /*
                         * The interval doesn't adjoin with the right interval.
                         * It must be added individually.
                         */
                        btree_insert(&a->used_space, page, (void *) count, leaf);
                        return 1;
                }
        }

        node = btree_leaf_node_right_neighbour(&a->used_space, leaf);
        if (node) {
                __address left_pg = leaf->key[leaf->keys - 1], right_pg = node->key[0];
                count_t left_cnt = (count_t) leaf->value[leaf->keys - 1], right_cnt = (count_t) node->value[0];
                
                /*
                 * Examine the possibility that the interval fits
                 * somewhere between the leftmost interval of
                 * the right neigbour and the last interval of the leaf.
                 */

                if (page < left_pg) {
                        /* Do nothing. */
                } else if (overlaps(page, count*PAGE_SIZE, left_pg, left_cnt*PAGE_SIZE)) {
                        /* The interval intersects with the left interval. */
                        return 0;
                } else if (overlaps(page, count*PAGE_SIZE, right_pg, right_cnt*PAGE_SIZE)) {
                        /* The interval intersects with the right interval. */
                        return 0;                       
                } else if ((page == left_pg + left_cnt*PAGE_SIZE) && (page + count*PAGE_SIZE == right_pg)) {
                        /* The interval can be added by merging the two already present intervals. */
                        leaf->value[leaf->keys - 1] += count + right_cnt;
                        btree_remove(&a->used_space, right_pg, node);
                        return 1; 
                } else if (page == left_pg + left_cnt*PAGE_SIZE) {
                        /* The interval can be added by simply growing the left interval. */
                        leaf->value[leaf->keys - 1] +=  count;
                        return 1;
                } else if (page + count*PAGE_SIZE == right_pg) {
                        /*
                         * The interval can be addded by simply moving base of the right
                         * interval down and increasing its size accordingly.
                         */
                        node->value[0] += count;
                        node->key[0] = page;
                        return 1;
                } else {
                        /*
                         * The interval is between both neigbouring intervals,
                         * but cannot be merged with any of them.
                         */
                        btree_insert(&a->used_space, page, (void *) count, leaf);
                        return 1;
                }
        } else if (page >= leaf->key[leaf->keys - 1]) {
                __address left_pg = leaf->key[leaf->keys - 1];
                count_t left_cnt = (count_t) leaf->value[leaf->keys - 1];
        
                /*
                 * Investigate the border case in which the right neighbour does not
                 * exist but the interval fits from the right.
                 */
                 
                if (overlaps(page, count*PAGE_SIZE, left_pg, left_cnt*PAGE_SIZE)) {
                        /* The interval intersects with the left interval. */
                        return 0;
                } else if (left_pg + left_cnt*PAGE_SIZE == page) {
                        /* The interval can be added by growing the left interval. */
                        leaf->value[leaf->keys - 1] += count;
                        return 1;
                } else {
                        /*
                         * The interval doesn't adjoin with the left interval.
                         * It must be added individually.
                         */
                        btree_insert(&a->used_space, page, (void *) count, leaf);
                        return 1;
                }
        }
        
        /*
         * Note that if the algorithm made it thus far, the interval can fit only
         * between two other intervals of the leaf. The two border cases were already
         * resolved.
         */
        for (i = 1; i < leaf->keys; i++) {
                if (page < leaf->key[i]) {
                        __address left_pg = leaf->key[i - 1], right_pg = leaf->key[i];
                        count_t left_cnt = (count_t) leaf->value[i - 1], right_cnt = (count_t) leaf->value[i];

                        /*
                         * The interval fits between left_pg and right_pg.
                         */

                        if (overlaps(page, count*PAGE_SIZE, left_pg, left_cnt*PAGE_SIZE)) {
                                /* The interval intersects with the left interval. */
                                return 0;
                        } else if (overlaps(page, count*PAGE_SIZE, right_pg, right_cnt*PAGE_SIZE)) {
                                /* The interval intersects with the right interval. */
                                return 0;                       
                        } else if ((page == left_pg + left_cnt*PAGE_SIZE) && (page + count*PAGE_SIZE == right_pg)) {
                                /* The interval can be added by merging the two already present intervals. */
                                leaf->value[i - 1] += count + right_cnt;
                                btree_remove(&a->used_space, right_pg, leaf);
                                return 1; 
                        } else if (page == left_pg + left_cnt*PAGE_SIZE) {
                                /* The interval can be added by simply growing the left interval. */
                                leaf->value[i - 1] += count;
                                return 1;
                        } else if (page + count*PAGE_SIZE == right_pg) {
                                /*
                                 * The interval can be addded by simply moving base of the right
                                 * interval down and increasing its size accordingly.
                                 */
                                leaf->value[i] += count;
                                leaf->key[i] = page;
                                return 1;
                        } else {
                                /*
                                 * The interval is between both neigbouring intervals,
                                 * but cannot be merged with any of them.
                                 */
                                btree_insert(&a->used_space, page, (void *) count, leaf);
                                return 1;
                        }
                }
        }

        panic("Inconsistency detected while adding %d pages of used space at %p.\n", count, page);
}

int used_space_remove(as_area_t *a, __address page, count_t count)
{
        btree_node_t *leaf, *node;
        count_t pages;
        int i;

        ASSERT(page == ALIGN_DOWN(page, PAGE_SIZE));
        ASSERT(count);

        pages = (count_t) btree_search(&a->used_space, page, &leaf);
        if (pages) {
                /*
                 * We are lucky, page is the beginning of some interval.
                 */
                if (count > pages) {
                        return 0;
                } else if (count == pages) {
                        btree_remove(&a->used_space, page, leaf);
                        return 1;
                } else {
                        /*
                         * Find the respective interval.
                         * Decrease its size and relocate its start address.
                         */
                        for (i = 0; i < leaf->keys; i++) {
                                if (leaf->key[i] == page) {
                                        leaf->key[i] += count*PAGE_SIZE;
                                        leaf->value[i] -= count;
                                        return 1;
                                }
                        }
                        goto error;
                }
        }

        node = btree_leaf_node_left_neighbour(&a->used_space, leaf);
        if (node && page < leaf->key[0]) {
                __address left_pg = node->key[node->keys - 1];
                count_t left_cnt = (count_t) node->value[node->keys - 1];

                if (overlaps(left_pg, left_cnt*PAGE_SIZE, page, count*PAGE_SIZE)) {
                        if (page + count*PAGE_SIZE == left_pg + left_cnt*PAGE_SIZE) {
                                /*
                                 * The interval is contained in the rightmost interval
                                 * of the left neighbour and can be removed by
                                 * updating the size of the bigger interval.
                                 */
                                node->value[node->keys - 1] -= count;
                                return 1;
                        } else if (page + count*PAGE_SIZE < left_pg + left_cnt*PAGE_SIZE) {
                                count_t new_cnt;
                                
                                /*
                                 * The interval is contained in the rightmost interval
                                 * of the left neighbour but its removal requires
                                 * both updating the size of the original interval and
                                 * also inserting a new interval.
                                 */
                                new_cnt = ((left_pg + left_cnt*PAGE_SIZE) - (page + count*PAGE_SIZE)) >> PAGE_WIDTH;
                                node->value[node->keys - 1] -= count + new_cnt;
                                btree_insert(&a->used_space, page + count*PAGE_SIZE, (void *) new_cnt, leaf);
                                return 1;
                        }
                }
                return 0;
        } else if (page < leaf->key[0]) {
                return 0;
        }
        
        if (page > leaf->key[leaf->keys - 1]) {
                __address left_pg = leaf->key[leaf->keys - 1];
                count_t left_cnt = (count_t) leaf->value[leaf->keys - 1];

                if (overlaps(left_pg, left_cnt*PAGE_SIZE, page, count*PAGE_SIZE)) {
                        if (page + count*PAGE_SIZE == left_pg + left_cnt*PAGE_SIZE) {
                                /*
                                 * The interval is contained in the rightmost interval
                                 * of the leaf and can be removed by updating the size
                                 * of the bigger interval.
                                 */
                                leaf->value[leaf->keys - 1] -= count;
                                return 1;
                        } else if (page + count*PAGE_SIZE < left_pg + left_cnt*PAGE_SIZE) {
                                count_t new_cnt;
                                
                                /*
                                 * The interval is contained in the rightmost interval
                                 * of the leaf but its removal requires both updating
                                 * the size of the original interval and
                                 * also inserting a new interval.
                                 */
                                new_cnt = ((left_pg + left_cnt*PAGE_SIZE) - (page + count*PAGE_SIZE)) >> PAGE_WIDTH;
                                leaf->value[leaf->keys - 1] -= count + new_cnt;
                                btree_insert(&a->used_space, page + count*PAGE_SIZE, (void *) new_cnt, leaf);
                                return 1;
                        }
                }
                return 0;
        }       
        
        /*
         * The border cases have been already resolved.
         * Now the interval can be only between intervals of the leaf. 
         */
        for (i = 1; i < leaf->keys - 1; i++) {
                if (page < leaf->key[i]) {
                        __address left_pg = leaf->key[i - 1];
                        count_t left_cnt = (count_t) leaf->value[i - 1];

                        /*
                         * Now the interval is between intervals corresponding to (i - 1) and i.
                         */
                        if (overlaps(left_pg, left_cnt*PAGE_SIZE, page, count*PAGE_SIZE)) {
                                if (page + count*PAGE_SIZE == left_pg + left_cnt*PAGE_SIZE) {
                                        /*
                                        * The interval is contained in the interval (i - 1)
                                         * of the leaf and can be removed by updating the size
                                         * of the bigger interval.
                                         */
                                        leaf->value[i - 1] -= count;
                                        return 1;
                                } else if (page + count*PAGE_SIZE < left_pg + left_cnt*PAGE_SIZE) {
                                        count_t new_cnt;
                                
                                        /*
                                         * The interval is contained in the interval (i - 1)
                                         * of the leaf but its removal requires both updating
                                         * the size of the original interval and
                                         * also inserting a new interval.
                                         */
                                        new_cnt = ((left_pg + left_cnt*PAGE_SIZE) - (page + count*PAGE_SIZE)) >> PAGE_WIDTH;
                                        leaf->value[i - 1] -= count + new_cnt;
                                        btree_insert(&a->used_space, page + count*PAGE_SIZE, (void *) new_cnt, leaf);
                                        return 1;
                                }
                        }
                        return 0;
                }
        }

error:
        panic("Inconsistency detected while removing %d pages of used space from %p.\n", count, page);
}

void sh_info_remove_reference(share_info_t *sh_info)
{
        bool dealloc = false;

        mutex_lock(&sh_info->lock);
        ASSERT(sh_info->refcount);
        if (--sh_info->refcount == 0) {
                dealloc = true;
                link_t *cur;
                
                /*
                 * Now walk carefully the pagemap B+tree and free/remove
                 * reference from all frames found there.
                 */
                for (cur = sh_info->pagemap.leaf_head.next; cur != &sh_info->pagemap.leaf_head; cur = cur->next) {
                        btree_node_t *node;
                        int i;
                        
                        node = list_get_instance(cur, btree_node_t, leaf_link);
                        for (i = 0; i < node->keys; i++) 
                                frame_free(ADDR2PFN((__address) node->value[i]));
                }
                
        }
        mutex_unlock(&sh_info->lock);
        
        if (dealloc) {
                btree_destroy(&sh_info->pagemap);
                free(sh_info);
        }
}

/*
 * Address space related syscalls.
 */

__native sys_as_area_create(__address address, size_t size, int flags)
{
        if (as_area_create(AS, flags | AS_AREA_CACHEABLE, size, address, AS_AREA_ATTR_NONE, &anon_backend, NULL))
                return (__native) address;
        else
                return (__native) -1;
}

__native sys_as_area_resize(__address address, size_t size, int flags)
{
        return (__native) as_area_resize(AS, address, size, 0);
}

__native sys_as_area_destroy(__address address)
{
        return (__native) as_area_destroy(AS, address);
}

---