// SPDX-License-Identifier: GPL-2.0
/*
 * linux/fs/ext4/readpage.c
 *
 * Copyright (C) 2002, Linus Torvalds.
 * Copyright (C) 2015, Google, Inc.
 *
 * This was originally taken from fs/mpage.c
 *
 * The ext4_mpage_readpages() function here is intended to
 * replace mpage_readahead() in the general case, not just for
 * encrypted files.  It has some limitations (see below), where it
 * will fall back to read_block_full_page(), but these limitations
 * should only be hit when page_size != block_size.
 *
 * This will allow us to attach a callback function to support ext4
 * encryption.
 *
 * If anything unusual happens, such as:
 *
 * - encountering a page which has buffers
 * - encountering a page which has a non-hole after a hole
 * - encountering a page with non-contiguous blocks
 *
 * then this code just gives up and calls the buffer_head-based read function.
 * It does handle a page which has holes at the end - that is a common case:
 * the end-of-file on blocksize < PAGE_SIZE setups.
 *
 */

#include <linux/kernel.h>
#include <linux/export.h>
#include <linux/mm.h>
#include <linux/kdev_t.h>
#include <linux/gfp.h>
#include <linux/bio.h>
#include <linux/fs.h>
#include <linux/buffer_head.h>
#include <linux/blkdev.h>
#include <linux/highmem.h>
#include <linux/prefetch.h>
#include <linux/mpage.h>
#include <linux/writeback.h>
#include <linux/backing-dev.h>
#include <linux/pagevec.h>

#include "ext4.h"

#define NUM_PREALLOC_POST_READ_CTXS     128

static struct kmem_cache *bio_post_read_ctx_cache;
static mempool_t *bio_post_read_ctx_pool;

/* postprocessing steps for read bios */
enum bio_post_read_step {
        STEP_INITIAL = 0,
        STEP_DECRYPT,
        STEP_VERITY,
        STEP_MAX,
};

struct bio_post_read_ctx {
        struct bio *bio;
        struct work_struct work;
        unsigned int cur_step;
        unsigned int enabled_steps;
};

static void __read_end_io(struct bio *bio)
{
        struct page *page;
        struct bio_vec *bv;
        struct bvec_iter_all iter_all;

        bio_for_each_segment_all(bv, bio, iter_all) {
                page = bv->bv_page;

                /* PG_error was set if any post_read step failed */
                if (bio->bi_status || PageError(page)) {
                        ClearPageUptodate(page);
                        /* will re-read again later */
                        ClearPageError(page);
                } else {
                        SetPageUptodate(page);
                }
                unlock_page(page);
        }
        if (bio->bi_private)
                mempool_free(bio->bi_private, bio_post_read_ctx_pool);
        bio_put(bio);
}

static void bio_post_read_processing(struct bio_post_read_ctx *ctx);

static void decrypt_work(struct work_struct *work)
{
        struct bio_post_read_ctx *ctx =
                container_of(work, struct bio_post_read_ctx, work);

        fscrypt_decrypt_bio(ctx->bio);

        bio_post_read_processing(ctx);
}

static void verity_work(struct work_struct *work)
{
        struct bio_post_read_ctx *ctx =
                container_of(work, struct bio_post_read_ctx, work);
        struct bio *bio = ctx->bio;

        /*
         * fsverity_verify_bio() may call readpages() again, and although verity
         * will be disabled for that, decryption may still be needed, causing
         * another bio_post_read_ctx to be allocated.  So to guarantee that
         * mempool_alloc() never deadlocks we must free the current ctx first.
         * This is safe because verity is the last post-read step.
         */
        BUILD_BUG_ON(STEP_VERITY + 1 != STEP_MAX);
        mempool_free(ctx, bio_post_read_ctx_pool);
        bio->bi_private = NULL;

        fsverity_verify_bio(bio);

        __read_end_io(bio);
}

static void bio_post_read_processing(struct bio_post_read_ctx *ctx)
{
        /*
         * We use different work queues for decryption and for verity because
         * verity may require reading metadata pages that need decryption, and
         * we shouldn't recurse to the same workqueue.
         */
        switch (++ctx->cur_step) {
        case STEP_DECRYPT:
                if (ctx->enabled_steps & (1 << STEP_DECRYPT)) {
                        INIT_WORK(&ctx->work, decrypt_work);
                        fscrypt_enqueue_decrypt_work(&ctx->work);
                        return;
                }
                ctx->cur_step++;
                fallthrough;
        case STEP_VERITY:
                if (ctx->enabled_steps & (1 << STEP_VERITY)) {
                        INIT_WORK(&ctx->work, verity_work);
                        fsverity_enqueue_verify_work(&ctx->work);
                        return;
                }
                ctx->cur_step++;
                fallthrough;
        default:
                __read_end_io(ctx->bio);
        }
}

static bool bio_post_read_required(struct bio *bio)
{
        return bio->bi_private && !bio->bi_status;
}

/*
 * I/O completion handler for multipage BIOs.
 *
 * The mpage code never puts partial pages into a BIO (except for end-of-file).
 * If a page does not map to a contiguous run of blocks then it simply falls
 * back to block_read_full_page().
 *
 * Why is this?  If a page's completion depends on a number of different BIOs
 * which can complete in any order (or at the same time) then determining the
 * status of that page is hard.  See end_buffer_async_read() for the details.
 * There is no point in duplicating all that complexity.
 */
static void mpage_end_io(struct bio *bio)
{
        if (bio_post_read_required(bio)) {
                struct bio_post_read_ctx *ctx = bio->bi_private;

                ctx->cur_step = STEP_INITIAL;
                bio_post_read_processing(ctx);
                return;
        }
        __read_end_io(bio);
}

static inline bool ext4_need_verity(const struct inode *inode, pgoff_t idx)
{
        return fsverity_active(inode) &&
               idx < DIV_ROUND_UP(inode->i_size, PAGE_SIZE);
}

static void ext4_set_bio_post_read_ctx(struct bio *bio,
                                       const struct inode *inode,
                                       pgoff_t first_idx)
{
        unsigned int post_read_steps = 0;

        if (fscrypt_inode_uses_fs_layer_crypto(inode))
                post_read_steps |= 1 << STEP_DECRYPT;

        if (ext4_need_verity(inode, first_idx))
                post_read_steps |= 1 << STEP_VERITY;

        if (post_read_steps) {
                /* Due to the mempool, this never fails. */
                struct bio_post_read_ctx *ctx =
                        mempool_alloc(bio_post_read_ctx_pool, GFP_NOFS);

                ctx->bio = bio;
                ctx->enabled_steps = post_read_steps;
                bio->bi_private = ctx;
        }
}

static inline loff_t ext4_readpage_limit(struct inode *inode)
{
        if (IS_ENABLED(CONFIG_FS_VERITY) &&
            (IS_VERITY(inode) || ext4_verity_in_progress(inode)))
                return inode->i_sb->s_maxbytes;

        return i_size_read(inode);
}

int ext4_mpage_readpages(struct inode *inode,
                struct readahead_control *rac, struct page *page)
{
        struct bio *bio = NULL;
        sector_t last_block_in_bio = 0;

        const unsigned blkbits = inode->i_blkbits;
        const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
        const unsigned blocksize = 1 << blkbits;
        sector_t next_block;
        sector_t block_in_file;
        sector_t last_block;
        sector_t last_block_in_file;
        sector_t blocks[MAX_BUF_PER_PAGE];
        unsigned page_block;
        struct block_device *bdev = inode->i_sb->s_bdev;
        int length;
        unsigned relative_block = 0;
        struct ext4_map_blocks map;
        unsigned int nr_pages = rac ? readahead_count(rac) : 1;

        map.m_pblk = 0;
        map.m_lblk = 0;
        map.m_len = 0;
        map.m_flags = 0;

        for (; nr_pages; nr_pages--) {
                int fully_mapped = 1;
                unsigned first_hole = blocks_per_page;

                if (rac) {
                        page = readahead_page(rac);
                        prefetchw(&page->flags);
                }

                if (page_has_buffers(page))
                        goto confused;

                block_in_file = next_block =
                        (sector_t)page->index << (PAGE_SHIFT - blkbits);
                last_block = block_in_file + nr_pages * blocks_per_page;
                last_block_in_file = (ext4_readpage_limit(inode) +
                                      blocksize - 1) >> blkbits;
                if (last_block > last_block_in_file)
                        last_block = last_block_in_file;
                page_block = 0;

                /*
                 * Map blocks using the previous result first.
                 */
                if ((map.m_flags & EXT4_MAP_MAPPED) &&
                    block_in_file > map.m_lblk &&
                    block_in_file < (map.m_lblk + map.m_len)) {
                        unsigned map_offset = block_in_file - map.m_lblk;
                        unsigned last = map.m_len - map_offset;

                        for (relative_block = 0; ; relative_block++) {
                                if (relative_block == last) {
                                        /* needed? */
                                        map.m_flags &= ~EXT4_MAP_MAPPED;
                                        break;
                                }
                                if (page_block == blocks_per_page)
                                        break;
                                blocks[page_block] = map.m_pblk + map_offset +
                                        relative_block;
                                page_block++;
                                block_in_file++;
                        }
                }

                /*
                 * Then do more ext4_map_blocks() calls until we are
                 * done with this page.
                 */
                while (page_block < blocks_per_page) {
                        if (block_in_file < last_block) {
                                map.m_lblk = block_in_file;
                                map.m_len = last_block - block_in_file;

                                if (ext4_map_blocks(NULL, inode, &map, 0) < 0) {
                                set_error_page:
                                        SetPageError(page);
                                        zero_user_segment(page, 0,
                                                          PAGE_SIZE);
                                        unlock_page(page);
                                        goto next_page;
                                }
                        }
                        if ((map.m_flags & EXT4_MAP_MAPPED) == 0) {
                                fully_mapped = 0;
                                if (first_hole == blocks_per_page)
                                        first_hole = page_block;
                                page_block++;
                                block_in_file++;
                                continue;
                        }
                        if (first_hole != blocks_per_page)
                                goto confused;          /* hole -> non-hole */

                        /* Contiguous blocks? */
                        if (page_block && blocks[page_block-1] != map.m_pblk-1)
                                goto confused;
                        for (relative_block = 0; ; relative_block++) {
                                if (relative_block == map.m_len) {
                                        /* needed? */
                                        map.m_flags &= ~EXT4_MAP_MAPPED;
                                        break;
                                } else if (page_block == blocks_per_page)
                                        break;
                                blocks[page_block] = map.m_pblk+relative_block;
                                page_block++;
                                block_in_file++;
                        }
                }
                if (first_hole != blocks_per_page) {
                        zero_user_segment(page, first_hole << blkbits,
                                          PAGE_SIZE);
                        if (first_hole == 0) {
                                if (ext4_need_verity(inode, page->index) &&
                                    !fsverity_verify_page(page))
                                        goto set_error_page;
                                SetPageUptodate(page);
                                unlock_page(page);
                                goto next_page;
                        }
                } else if (fully_mapped) {
                        SetPageMappedToDisk(page);
                }

                /*
                 * This page will go to BIO.  Do we need to send this
                 * BIO off first?
                 */
                if (bio && (last_block_in_bio != blocks[0] - 1 ||
                            !fscrypt_mergeable_bio(bio, inode, next_block))) {
                submit_and_realloc:
                        submit_bio(bio);
                        bio = NULL;
                }
                if (bio == NULL) {
                        /*
                         * bio_alloc will _always_ be able to allocate a bio if
                         * __GFP_DIRECT_RECLAIM is set, see bio_alloc_bioset().
                         */
                        bio = bio_alloc(GFP_KERNEL, bio_max_segs(nr_pages));
                        fscrypt_set_bio_crypt_ctx(bio, inode, next_block,
                                                  GFP_KERNEL);
                        ext4_set_bio_post_read_ctx(bio, inode, page->index);
                        bio_set_dev(bio, bdev);
                        bio->bi_iter.bi_sector = blocks[0] << (blkbits - 9);
                        bio->bi_end_io = mpage_end_io;
                        bio_set_op_attrs(bio, REQ_OP_READ,
                                                rac ? REQ_RAHEAD : 0);
                }

                length = first_hole << blkbits;
                if (bio_add_page(bio, page, length, 0) < length)
                        goto submit_and_realloc;

                if (((map.m_flags & EXT4_MAP_BOUNDARY) &&
                     (relative_block == map.m_len)) ||
                    (first_hole != blocks_per_page)) {
                        submit_bio(bio);
                        bio = NULL;
                } else
                        last_block_in_bio = blocks[blocks_per_page - 1];
                goto next_page;
        confused:
                if (bio) {
                        submit_bio(bio);
                        bio = NULL;
                }
                if (!PageUptodate(page))
                        block_read_full_page(page, ext4_get_block);
                else
                        unlock_page(page);
        next_page:
                if (rac)
                        put_page(page);
        }
        if (bio)
                submit_bio(bio);
        return 0;
}

int __init ext4_init_post_read_processing(void)
{
        bio_post_read_ctx_cache =
                kmem_cache_create("ext4_bio_post_read_ctx",
                                  sizeof(struct bio_post_read_ctx), 0, 0, NULL);
        if (!bio_post_read_ctx_cache)
                goto fail;
        bio_post_read_ctx_pool =
                mempool_create_slab_pool(NUM_PREALLOC_POST_READ_CTXS,
                                         bio_post_read_ctx_cache);
        if (!bio_post_read_ctx_pool)
                goto fail_free_cache;
        return 0;

fail_free_cache:
        kmem_cache_destroy(bio_post_read_ctx_cache);
fail:
        return -ENOMEM;
}

void ext4_exit_post_read_processing(void)
{
        mempool_destroy(bio_post_read_ctx_pool);
        kmem_cache_destroy(bio_post_read_ctx_cache);
}