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1424 jermar 1 
/*
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 * Copyright (C) 2006 Jakub Jermar
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 * All rights reserved.
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 *
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 * Redistribution and use in source and binary forms, with or without
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 * modification, are permitted provided that the following conditions
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 * are met:
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 *
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 * - Redistributions of source code must retain the above copyright
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 *   notice, this list of conditions and the following disclaimer.
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 * - Redistributions in binary form must reproduce the above copyright
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 *   notice, this list of conditions and the following disclaimer in the
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 *   documentation and/or other materials provided with the distribution.
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 * - The name of the author may not be used to endorse or promote products
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 *   derived from this software without specific prior written permission.
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 *
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 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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 */
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/**
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 * @file    backend_anon.c
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 * @brief   Backend for anonymous memory address space areas.
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 *
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 */
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#include <mm/as.h>
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#include <mm/page.h>
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#include <genarch/mm/page_pt.h>
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#include <genarch/mm/page_ht.h>
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#include <mm/frame.h>
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#include <mm/slab.h>
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#include <synch/mutex.h>
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#include <adt/list.h>
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#include <adt/btree.h>
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#include <errno.h>
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#include <arch/types.h>
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#include <typedefs.h>
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#include <align.h>
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#include <arch.h>
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static int anon_page_fault(as_area_t *area, __address addr, pf_access_t access);
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static void anon_frame_free(as_area_t *area, __address page, __address frame);
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static void anon_share(as_area_t *area);
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mem_backend_t anon_backend = {
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    .page_fault = anon_page_fault,
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    .frame_free = anon_frame_free,
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    .share = anon_share
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};
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/** Service a page fault in the anonymous memory address space area.
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 *
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 * The address space area and page tables must be already locked.
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 *
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 * @param area Pointer to the address space area.
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 * @param addr Faulting virtual address.
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 * @param access Access mode that caused the fault (i.e. read/write/exec).
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 *
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 * @return AS_PF_FAULT on failure (i.e. page fault) or AS_PF_OK on success (i.e. serviced).
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 */
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int anon_page_fault(as_area_t *area, __address addr, pf_access_t access)
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{
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    __address frame;
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    if (!as_area_check_access(area, access))
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        return AS_PF_FAULT;
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    if (area->sh_info) {
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        btree_node_t *leaf;
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        /*
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         * The area is shared, chances are that the mapping can be found
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         * in the pagemap of the address space area share info structure.
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         * In the case that the pagemap does not contain the respective
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         * mapping, a new frame is allocated and the mapping is created.
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         */
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        mutex_lock(&area->sh_info->lock);
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        frame = (__address) btree_search(&area->sh_info->pagemap,
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            ALIGN_DOWN(addr, PAGE_SIZE) - area->base, &leaf);
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        if (!frame) {
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            bool allocate = true;
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            int i;
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            /*
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             * Zero can be returned as a valid frame address.
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             * Just a small workaround.
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             */
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            for (i = 0; i < leaf->keys; i++) {
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                if (leaf->key[i] == ALIGN_DOWN(addr, PAGE_SIZE)) {
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                    allocate = false;
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                    break;
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                }
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            }
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            if (allocate) {
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                frame = PFN2ADDR(frame_alloc(ONE_FRAME, 0));
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                memsetb(PA2KA(frame), FRAME_SIZE, 0);
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                /*
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                 * Insert the address of the newly allocated frame to the pagemap.
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                 */
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                btree_insert(&area->sh_info->pagemap, ALIGN_DOWN(addr, PAGE_SIZE) - area->base, (void *) frame, leaf);
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            }
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        }
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        mutex_unlock(&area->sh_info->lock);
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    } else {
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        /*
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         * In general, there can be several reasons that
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         * can have caused this fault.
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         *
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         * - non-existent mapping: the area is an anonymous
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         *   area (e.g. heap or stack) and so far has not been
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         *   allocated a frame for the faulting page
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         *
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         * - non-present mapping: another possibility,
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         *   currently not implemented, would be frame
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         *   reuse; when this becomes a possibility,
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         *   do not forget to distinguish between
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         *   the different causes
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         */
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        frame = PFN2ADDR(frame_alloc(ONE_FRAME, 0));
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        memsetb(PA2KA(frame), FRAME_SIZE, 0);
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    }
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    /*
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     * Map 'page' to 'frame'.
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     * Note that TLB shootdown is not attempted as only new information is being
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     * inserted into page tables.
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     */
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    page_mapping_insert(AS, addr, frame, as_area_get_flags(area));
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    if (!used_space_insert(area, ALIGN_DOWN(addr, PAGE_SIZE), 1))
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        panic("Could not insert used space.\n");
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    return AS_PF_OK;
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}
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/** Free a frame that is backed by the anonymous memory backend.
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 *
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 * The address space area and page tables must be already locked.
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 *
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 * @param area Ignored.
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 * @param page Ignored.
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 * @param frame Frame to be released.
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 */
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void anon_frame_free(as_area_t *area, __address page, __address frame)
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{
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    frame_free(ADDR2PFN(frame));
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}
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/** Share the anonymous address space area.
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 *
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 * Sharing of anonymous area is done by duplicating its entire mapping
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 * to the pagemap. Page faults will primarily search for frames there.
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 *
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 * The address space and address space area must be already locked.
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 *
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 * @param area Address space area to be shared.
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 */
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void anon_share(as_area_t *area)
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{
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    link_t *cur;
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    /*
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     * Copy used portions of the area to sh_info's page map.
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     */
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    mutex_lock(&area->sh_info->lock);
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    for (cur = area->used_space.leaf_head.next; cur != &area->used_space.leaf_head; cur = cur->next) {
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        btree_node_t *node;
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        int i;
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        node = list_get_instance(cur, btree_node_t, leaf_link);
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        for (i = 0; i < node->keys; i++) {
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            __address base = node->key[i];
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            count_t count = (count_t) node->value[i];
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            int j;
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            for (j = 0; j < count; j++) {
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                pte_t *pte;
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                page_table_lock(area->as, false);
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                pte = page_mapping_find(area->as, base + j*PAGE_SIZE);
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                ASSERT(pte && PTE_VALID(pte) && PTE_PRESENT(pte));
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                btree_insert(&area->sh_info->pagemap, (base + j*PAGE_SIZE) - area->base,
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                    (void *) PTE_GET_FRAME(pte), NULL);
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                page_table_unlock(area->as, false);
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            }
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        }
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    }
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    mutex_unlock(&area->sh_info->lock);
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}