source: mainline/kernel/generic/src/mm/backend_elf.c@ 3ca0a2d

/*
 * 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 kernel_generic_mm
 * @{
 */

/**
 * @file
 * @brief       Backend for address space areas backed by an ELF image.
 */

#include <lib/elf.h>
#include <assert.h>
#include <typedefs.h>
#include <mm/as.h>
#include <mm/frame.h>
#include <mm/slab.h>
#include <mm/page.h>
#include <mm/reserve.h>
#include <mm/km.h>
#include <genarch/mm/page_pt.h>
#include <genarch/mm/page_ht.h>
#include <align.h>
#include <mem.h>
#include <macros.h>
#include <arch.h>
#include <barrier.h>

static bool elf_create(as_area_t *);
static bool elf_resize(as_area_t *, size_t);
static void elf_share(as_area_t *);
static void elf_destroy(as_area_t *);

static bool elf_is_resizable(as_area_t *);
static bool elf_is_shareable(as_area_t *);

static int elf_page_fault(as_area_t *, uintptr_t, pf_access_t);
static void elf_frame_free(as_area_t *, uintptr_t, uintptr_t);

mem_backend_t elf_backend = {
        .create = elf_create,
        .resize = elf_resize,
        .share = elf_share,
        .destroy = elf_destroy,

        .is_resizable = elf_is_resizable,
        .is_shareable = elf_is_shareable,

        .page_fault = elf_page_fault,
        .frame_free = elf_frame_free,

        .create_shared_data = NULL,
        .destroy_shared_data = NULL
};

static size_t elf_nonanon_pages_get(as_area_t *area)
{
        elf_segment_header_t *entry = area->backend_data.segment;
        uintptr_t first = ALIGN_UP(entry->p_vaddr, PAGE_SIZE);
        uintptr_t last = ALIGN_DOWN(entry->p_vaddr + entry->p_filesz,
            PAGE_SIZE);

        if (entry->p_flags & PF_W)
                return 0;

        if (last < first)
                return 0;

        return last - first;
}

/** Get page number in the task where the ELF page originates from.
 *
 * The ELF page can be shared to a different address than it originated from,
 * but we need the originating address since that corresponds to the ELF's
 * virtual addesses.
 *
 * @param area Area in which the page resides
 * @param page Virtual address of the page in @a area
 * @return Virtual address of the page in the origin address space
 */
static uintptr_t elf_orig_page(as_area_t *area, uintptr_t page)
{
        return page - area->base + area->backend_data.elf_base;
}

bool elf_create(as_area_t *area)
{
        size_t nonanon_pages = elf_nonanon_pages_get(area);

        if (area->pages <= nonanon_pages)
                return true;

        return reserve_try_alloc(area->pages - nonanon_pages);
}

bool elf_resize(as_area_t *area, size_t new_pages)
{
        size_t nonanon_pages = elf_nonanon_pages_get(area);

        if (new_pages > area->pages) {
                /* The area is growing. */
                if (area->pages >= nonanon_pages)
                        return reserve_try_alloc(new_pages - area->pages);
                else if (new_pages > nonanon_pages)
                        return reserve_try_alloc(new_pages - nonanon_pages);
        } else if (new_pages < area->pages) {
                /* The area is shrinking. */
                if (new_pages >= nonanon_pages)
                        reserve_free(area->pages - new_pages);
                else if (area->pages > nonanon_pages)
                        reserve_free(nonanon_pages - new_pages);
        }

        return true;
}

/** 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.
 *
 * @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;

        assert(mutex_locked(&area->as->lock));
        assert(mutex_locked(&area->lock));

        /*
         * Find the node in which to start linear search.
         */
        if (area->flags & AS_AREA_WRITE) {
                node = list_get_instance(list_first(&area->used_space.leaf_list),
                    btree_node_t, leaf_link);
        } else {
                (void) btree_search(&area->used_space, start_anon, &leaf);
                node = btree_leaf_node_left_neighbour(&area->used_space, 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_list.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];
                        size_t count = (size_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 + P2SZ(count) <= start_anon)
                                        continue;

                        for (j = 0; j < count; j++) {
                                pte_t pte;
                                bool found;

                                /*
                                 * Skip read-only pages that are backed by the
                                 * ELF image.
                                 */
                                if (!(area->flags & AS_AREA_WRITE))
                                        if (base >= entry->p_vaddr &&
                                            base + P2SZ(j + 1) <= start_anon)
                                                continue;

                                page_table_lock(area->as, false);
                                found = page_mapping_find(area->as,
                                    base + P2SZ(j), false, &pte);

                                (void) found;
                                assert(found);
                                assert(PTE_VALID(&pte));
                                assert(PTE_PRESENT(&pte));

                                btree_insert(&area->sh_info->pagemap,
                                    (base + P2SZ(j)) - 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);
}

void elf_destroy(as_area_t *area)
{
        size_t nonanon_pages = elf_nonanon_pages_get(area);

        if (area->pages > nonanon_pages)
                reserve_free(area->pages - nonanon_pages);
}

bool elf_is_resizable(as_area_t *area)
{
        return true;
}

bool elf_is_shareable(as_area_t *area)
{
        return true;
}

/** 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 upage         Faulting virtual page.
 * @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 upage, 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;
        uintptr_t frame;
        uintptr_t kpage;
        uintptr_t start_anon;
        uintptr_t elfpage;
        size_t i;
        bool dirty = false;

        assert(page_table_locked(AS));
        assert(mutex_locked(&area->lock));
        assert(IS_ALIGNED(upage, PAGE_SIZE));

        elfpage = elf_orig_page(area, upage);

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

        if (elfpage < ALIGN_DOWN(entry->p_vaddr, PAGE_SIZE))
                return AS_PF_FAULT;

        if (elfpage >= entry->p_vaddr + entry->p_memsz)
                return AS_PF_FAULT;

        i = (elfpage - ALIGN_DOWN(entry->p_vaddr, PAGE_SIZE)) >>
            PAGE_WIDTH;
        base = (uintptr_t)
            (((void *) elf) + ALIGN_DOWN(entry->p_offset, PAGE_SIZE));

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

        mutex_lock(&area->sh_info->lock);
        if (area->sh_info->shared) {
                bool found = false;

                /*
                 * The address space area is shared.
                 */

                frame = (uintptr_t) btree_search(&area->sh_info->pagemap,
                    upage - area->base, &leaf);
                if (!frame) {
                        unsigned int i;

                        /*
                         * Workaround for valid NULL address.
                         */

                        for (i = 0; i < leaf->keys; i++) {
                                if (leaf->key[i] == upage - area->base) {
                                        found = true;
                                        break;
                                }
                        }
                }
                if (frame || found) {
                        frame_reference_add(ADDR2PFN(frame));
                        page_mapping_insert(AS, upage, frame,
                            as_area_get_flags(area));
                        if (!used_space_insert(area, upage, 1))
                                panic("Cannot insert used space.");
                        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 (elfpage >= entry->p_vaddr && elfpage + 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 instances 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) {
                        kpage = km_temporary_page_get(&frame, FRAME_NO_RESERVE);
                        memcpy((void *) kpage, (void *) (base + i * PAGE_SIZE),
                            PAGE_SIZE);
                        if (entry->p_flags & PF_X) {
                                smc_coherence((void *) kpage, PAGE_SIZE);
                        }
                        km_temporary_page_put(kpage);
                        dirty = true;
                } else {
                        pte_t pte;
                        bool found;

                        found = page_mapping_find(AS_KERNEL,
                            base + i * FRAME_SIZE, true, &pte);

                        (void) found;
                        assert(found);
                        assert(PTE_PRESENT(&pte));

                        frame = PTE_GET_FRAME(&pte);
                }
        } else if (elfpage >= 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.
                 */
                kpage = km_temporary_page_get(&frame, FRAME_NO_RESERVE);
                memsetb((void *) kpage, PAGE_SIZE, 0);
                km_temporary_page_put(kpage);
                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 (upage < entry->p_vaddr)
                        pad_lo = entry->p_vaddr - upage;
                else
                        pad_lo = 0;

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

                kpage = km_temporary_page_get(&frame, FRAME_NO_RESERVE);
                memcpy((void *) (kpage + pad_lo),
                    (void *) (base + i * PAGE_SIZE + pad_lo),
                    PAGE_SIZE - pad_lo - pad_hi);
                if (entry->p_flags & PF_X) {
                        smc_coherence((void *) (kpage + pad_lo),
                            PAGE_SIZE - pad_lo - pad_hi);
                }
                memsetb((void *) kpage, pad_lo, 0);
                memsetb((void *) (kpage + PAGE_SIZE - pad_hi), pad_hi, 0);
                km_temporary_page_put(kpage);
                dirty = true;
        }

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

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

        page_mapping_insert(AS, upage, frame, as_area_get_flags(area));
        if (!used_space_insert(area, upage, 1))
                panic("Cannot insert used space.");

        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_segment_header_t *entry = area->backend_data.segment;
        uintptr_t start_anon;
        uintptr_t elfpage;

        assert(page_table_locked(area->as));
        assert(mutex_locked(&area->lock));

        elfpage = elf_orig_page(area, page);

        assert(elfpage >= ALIGN_DOWN(entry->p_vaddr, PAGE_SIZE));
        assert(elfpage < entry->p_vaddr + entry->p_memsz);

        start_anon = entry->p_vaddr + entry->p_filesz;

        if (elfpage >= entry->p_vaddr && elfpage + PAGE_SIZE <= start_anon) {
                if (entry->p_flags & PF_W) {
                        /*
                         * Free the frame with the copy of writable segment
                         * data.
                         */
                        frame_free_noreserve(frame, 1);
                }
        } 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_noreserve(frame, 1);
        }
}

/** @}
 */