source: mainline/kernel/generic/src/mm/backend_elf.c@ 1cc2974

/*
 * Copyright (c) 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       Backend for address space areas backed by an ELF image.
 */

#include <lib/elf.h>
#include <debug.h>
#include <arch/types.h>
#include <mm/as.h>
#include <mm/frame.h>
#include <mm/slab.h>
#include <mm/page.h>
#include <genarch/mm/page_pt.h>
#include <genarch/mm/page_ht.h>
#include <align.h>
#include <memstr.h>
#include <macros.h>
#include <arch.h>

#ifdef CONFIG_VIRT_IDX_DCACHE
#include <arch/mm/cache.h>
#endif

static int elf_page_fault(as_area_t *area, uintptr_t addr, pf_access_t access);
static void elf_frame_free(as_area_t *area, uintptr_t page, uintptr_t frame);
static void elf_share(as_area_t *area);

mem_backend_t elf_backend = {
        .page_fault = elf_page_fault,
        .frame_free = elf_frame_free,
        .share = elf_share
};

/** Service a page fault in the ELF backend address space area.
 *
 * The address space area and page tables must be already locked.
 *
 * @param area Pointer to the address space area.
 * @param addr Faulting virtual address.
 * @param access Access mode that caused the fault (i.e. read/write/exec).
 *
 * @return AS_PF_FAULT on failure (i.e. page fault) or AS_PF_OK on success (i.e.
 *     serviced).
 */
int elf_page_fault(as_area_t *area, uintptr_t addr, pf_access_t access)
{
        elf_header_t *elf = area->backend_data.elf;
        elf_segment_header_t *entry = area->backend_data.segment;
        btree_node_t *leaf;
        uintptr_t base, frame, page, start_anon;
        index_t i;
        bool dirty = false;

        if (!as_area_check_access(area, access))
                return AS_PF_FAULT;

        ASSERT((addr >= ALIGN_DOWN(entry->p_vaddr, PAGE_SIZE)) &&
            (addr < entry->p_vaddr + entry->p_memsz));
        i = (addr - ALIGN_DOWN(entry->p_vaddr, PAGE_SIZE)) >> PAGE_WIDTH;
        base = (uintptr_t)
            (((void *) elf) + ALIGN_DOWN(entry->p_offset, PAGE_SIZE));

        /* Virtual address of faulting page*/
        page = ALIGN_DOWN(addr, PAGE_SIZE);

        /* Virtual address of the end of initialized part of segment */
        start_anon = entry->p_vaddr + entry->p_filesz;

        if (area->sh_info) {
                bool found = false;

                /*
                 * The address space area is shared.
                 */
                
                mutex_lock(&area->sh_info->lock);
                frame = (uintptr_t) btree_search(&area->sh_info->pagemap,
                    page - area->base, &leaf);
                if (!frame) {
                        unsigned int i;

                        /*
                         * Workaround for valid NULL address.
                         */

                        for (i = 0; i < leaf->keys; i++) {
                                if (leaf->key[i] == page) {
                                        found = true;
                                        break;
                                }
                        }
                }
                if (frame || found) {
                        frame_reference_add(ADDR2PFN(frame));
                        page_mapping_insert(AS, addr, frame,
                            as_area_get_flags(area));
                        if (!used_space_insert(area, page, 1))
                                panic("Could not insert used space.\n");
                        mutex_unlock(&area->sh_info->lock);
                        return AS_PF_OK;
                }
        }

        /*
         * The area is either not shared or the pagemap does not contain the
         * mapping.
         */
        if (page >= entry->p_vaddr && page + PAGE_SIZE <= start_anon) {
                /*
                 * Initialized portion of the segment. The memory is backed
                 * directly by the content of the ELF image. Pages are
                 * only copied if the segment is writable so that there
                 * can be more instantions of the same memory ELF image
                 * used at a time. Note that this could be later done
                 * as COW.
                 */
                if (entry->p_flags & PF_W) {
                        frame = (uintptr_t)frame_alloc(ONE_FRAME, 0);
                        memcpy((void *) PA2KA(frame),
                            (void *) (base + i * FRAME_SIZE), FRAME_SIZE);
                        dirty = true;
                } else {
                        frame = KA2PA(base + i * FRAME_SIZE);
                }       
        } else if (page >= start_anon) {
                /*
                 * This is the uninitialized portion of the segment.
                 * It is not physically present in the ELF image.
                 * To resolve the situation, a frame must be allocated
                 * and cleared.
                 */
                frame = (uintptr_t)frame_alloc(ONE_FRAME, 0);
                memsetb(PA2KA(frame), FRAME_SIZE, 0);
                dirty = true;
        } else {
                size_t pad_lo, pad_hi;
                /*
                 * The mixed case.
                 *
                 * The middle part is backed by the ELF image and
                 * the lower and upper parts are anonymous memory.
                 * (The segment can be and often is shorter than 1 page).
                 */
                if (page < entry->p_vaddr)
                        pad_lo = entry->p_vaddr - page;
                else
                        pad_lo = 0;

                if (start_anon < page + PAGE_SIZE)
                        pad_hi = page + PAGE_SIZE - start_anon;
                else
                        pad_hi = 0;

                frame = (uintptr_t)frame_alloc(ONE_FRAME, 0);
                memcpy((void *) (PA2KA(frame) + pad_lo),
                    (void *) (base + i * FRAME_SIZE + pad_lo),
                    FRAME_SIZE - pad_lo - pad_hi);
                memsetb(PA2KA(frame), pad_lo, 0);
                memsetb(PA2KA(frame) + FRAME_SIZE - pad_hi, pad_hi, 0);
                dirty = true;
        }

        if (dirty && area->sh_info) {
                frame_reference_add(ADDR2PFN(frame));
                btree_insert(&area->sh_info->pagemap, page - area->base,
                    (void *) frame, leaf);
        }

        if (area->sh_info)
                mutex_unlock(&area->sh_info->lock);

        page_mapping_insert(AS, addr, frame, as_area_get_flags(area));
        if (!used_space_insert(area, page, 1))
                panic("Could not insert used space.\n");

        return AS_PF_OK;
}

/** Free a frame that is backed by the ELF backend.
 *
 * The address space area and page tables must be already locked.
 *
 * @param area Pointer to the address space area.
 * @param page Page that is mapped to frame. Must be aligned to PAGE_SIZE.
 * @param frame Frame to be released.
 *
 */
void elf_frame_free(as_area_t *area, uintptr_t page, uintptr_t frame)
{
        elf_header_t *elf = area->backend_data.elf;
        elf_segment_header_t *entry = area->backend_data.segment;
        uintptr_t base, start_anon;
        index_t i;

        ASSERT((page >= ALIGN_DOWN(entry->p_vaddr, PAGE_SIZE)) &&
            (page < entry->p_vaddr + entry->p_memsz));
        i = (page - ALIGN_DOWN(entry->p_vaddr, PAGE_SIZE)) >> PAGE_WIDTH;
        base = (uintptr_t) (((void *) elf) +
            ALIGN_DOWN(entry->p_offset, FRAME_SIZE));
        start_anon = entry->p_vaddr + entry->p_filesz;

        if (page >= entry->p_vaddr && page + PAGE_SIZE <= start_anon) {
                if (entry->p_flags & PF_W) {
                        /*
                         * Free the frame with the copy of writable segment
                         * data.
                         */
                        frame_free(frame);
                }
        } else {
                /*
                 * The frame is either anonymous memory or the mixed case (i.e.
                 * lower part is backed by the ELF image and the upper is
                 * anonymous). In any case, a frame needs to be freed.
                 */ 
                frame_free(frame);
        }
}

/** Share ELF image backed address space area.
 *
 * If the area is writable, then all mapped pages are duplicated in the pagemap.
 * Otherwise only portions of the area that are not backed by the ELF image
 * are put into the pagemap.
 *
 * The address space and address space area must be locked prior to the call.
 *
 * @param area Address space area.
 */
void elf_share(as_area_t *area)
{
        elf_segment_header_t *entry = area->backend_data.segment;
        link_t *cur;
        btree_node_t *leaf, *node;
        uintptr_t start_anon = entry->p_vaddr + entry->p_filesz;

        /*
         * Find the node in which to start linear search.
         */
        if (area->flags & AS_AREA_WRITE) {
                node = list_get_instance(area->used_space.leaf_head.next,
                    btree_node_t, leaf_link);
        } else {
                (void) btree_search(&area->sh_info->pagemap, start_anon, &leaf);
                node = btree_leaf_node_left_neighbour(&area->sh_info->pagemap,
                    leaf);
                if (!node)
                        node = leaf;
        }

        /*
         * Copy used anonymous portions of the area to sh_info's page map.
         */
        mutex_lock(&area->sh_info->lock);
        for (cur = &node->leaf_link; cur != &area->used_space.leaf_head;
            cur = cur->next) {
                unsigned int i;
                
                node = list_get_instance(cur, btree_node_t, leaf_link);
                
                for (i = 0; i < node->keys; i++) {
                        uintptr_t base = node->key[i];
                        count_t count = (count_t) node->value[i];
                        unsigned int j;
                        
                        /*
                         * Skip read-only areas of used space that are backed
                         * by the ELF image.
                         */
                        if (!(area->flags & AS_AREA_WRITE))
                                if (base >= entry->p_vaddr &&
                                    base + count * PAGE_SIZE <= start_anon)
                                        continue;
                        
                        for (j = 0; j < count; j++) {
                                pte_t *pte;
                        
                                /*
                                 * Skip read-only pages that are backed by the
                                 * ELF image.
                                 */
                                if (!(area->flags & AS_AREA_WRITE))
                                        if (base >= entry->p_vaddr &&
                                            base + (j + 1) * PAGE_SIZE <=
                                            start_anon)
                                                continue;
                                
                                page_table_lock(area->as, false);
                                pte = page_mapping_find(area->as,
                                    base + j * PAGE_SIZE);
                                ASSERT(pte && PTE_VALID(pte) &&
                                    PTE_PRESENT(pte));
                                btree_insert(&area->sh_info->pagemap,
                                    (base + j * PAGE_SIZE) - area->base,
                                    (void *) PTE_GET_FRAME(pte), NULL);
                                page_table_unlock(area->as, false);

                                pfn_t pfn = ADDR2PFN(PTE_GET_FRAME(pte));
                                frame_reference_add(pfn);
                        }
                                
                }
        }
        mutex_unlock(&area->sh_info->lock);
}

/** @}
 */