// SPDX-License-Identifier: GPL-2.0
/*
 * Request reply cache. This is currently a global cache, but this may
 * change in the future and be a per-client cache.
 *
 * This code is heavily inspired by the 44BSD implementation, although
 * it does things a bit differently.
 *
 * Copyright (C) 1995, 1996 Olaf Kirch <okir@monad.swb.de>
 */

#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/sunrpc/addr.h>
#include <linux/highmem.h>
#include <linux/log2.h>
#include <linux/hash.h>
#include <net/checksum.h>

#include "nfsd.h"
#include "cache.h"

#define NFSDDBG_FACILITY        NFSDDBG_REPCACHE

/*
 * We use this value to determine the number of hash buckets from the max
 * cache size, the idea being that when the cache is at its maximum number
 * of entries, then this should be the average number of entries per bucket.
 */
#define TARGET_BUCKET_SIZE      64

struct nfsd_drc_bucket {
        struct list_head lru_head;
        spinlock_t cache_lock;
};

static struct nfsd_drc_bucket   *drc_hashtbl;
static struct kmem_cache        *drc_slab;

/* max number of entries allowed in the cache */
static unsigned int             max_drc_entries;

/* number of significant bits in the hash value */
static unsigned int             maskbits;
static unsigned int             drc_hashsize;

/*
 * Stats and other tracking of on the duplicate reply cache. All of these and
 * the "rc" fields in nfsdstats are protected by the cache_lock
 */

/* total number of entries */
static atomic_t                 num_drc_entries;

/* cache misses due only to checksum comparison failures */
static unsigned int             payload_misses;

/* amount of memory (in bytes) currently consumed by the DRC */
static unsigned int             drc_mem_usage;

/* longest hash chain seen */
static unsigned int             longest_chain;

/* size of cache when we saw the longest hash chain */
static unsigned int             longest_chain_cachesize;

static int      nfsd_cache_append(struct svc_rqst *rqstp, struct kvec *vec);
static unsigned long nfsd_reply_cache_count(struct shrinker *shrink,
                                            struct shrink_control *sc);
static unsigned long nfsd_reply_cache_scan(struct shrinker *shrink,
                                           struct shrink_control *sc);

static struct shrinker nfsd_reply_cache_shrinker = {
        .scan_objects = nfsd_reply_cache_scan,
        .count_objects = nfsd_reply_cache_count,
        .seeks  = 1,
};

/*
 * Put a cap on the size of the DRC based on the amount of available
 * low memory in the machine.
 *
 *  64MB:    8192
 * 128MB:   11585
 * 256MB:   16384
 * 512MB:   23170
 *   1GB:   32768
 *   2GB:   46340
 *   4GB:   65536
 *   8GB:   92681
 *  16GB:  131072
 *
 * ...with a hard cap of 256k entries. In the worst case, each entry will be
 * ~1k, so the above numbers should give a rough max of the amount of memory
 * used in k.
 */
static unsigned int
nfsd_cache_size_limit(void)
{
        unsigned int limit;
        unsigned long low_pages = totalram_pages - totalhigh_pages;

        limit = (16 * int_sqrt(low_pages)) << (PAGE_SHIFT-10);
        return min_t(unsigned int, limit, 256*1024);
}

/*
 * Compute the number of hash buckets we need. Divide the max cachesize by
 * the "target" max bucket size, and round up to next power of two.
 */
static unsigned int
nfsd_hashsize(unsigned int limit)
{
        return roundup_pow_of_two(limit / TARGET_BUCKET_SIZE);
}

static u32
nfsd_cache_hash(__be32 xid)
{
        return hash_32(be32_to_cpu(xid), maskbits);
}

static struct svc_cacherep *
nfsd_reply_cache_alloc(void)
{
        struct svc_cacherep     *rp;

        rp = kmem_cache_alloc(drc_slab, GFP_KERNEL);
        if (rp) {
                rp->c_state = RC_UNUSED;
                rp->c_type = RC_NOCACHE;
                INIT_LIST_HEAD(&rp->c_lru);
        }
        return rp;
}

static void
nfsd_reply_cache_free_locked(struct svc_cacherep *rp)
{
        if (rp->c_type == RC_REPLBUFF && rp->c_replvec.iov_base) {
                drc_mem_usage -= rp->c_replvec.iov_len;
                kfree(rp->c_replvec.iov_base);
        }
        list_del(&rp->c_lru);
        atomic_dec(&num_drc_entries);
        drc_mem_usage -= sizeof(*rp);
        kmem_cache_free(drc_slab, rp);
}

static void
nfsd_reply_cache_free(struct nfsd_drc_bucket *b, struct svc_cacherep *rp)
{
        spin_lock(&b->cache_lock);
        nfsd_reply_cache_free_locked(rp);
        spin_unlock(&b->cache_lock);
}

int nfsd_reply_cache_init(void)
{
        unsigned int hashsize;
        unsigned int i;
        int status = 0;

        max_drc_entries = nfsd_cache_size_limit();
        atomic_set(&num_drc_entries, 0);
        hashsize = nfsd_hashsize(max_drc_entries);
        maskbits = ilog2(hashsize);

        status = register_shrinker(&nfsd_reply_cache_shrinker);
        if (status)
                return status;

        drc_slab = kmem_cache_create("nfsd_drc", sizeof(struct svc_cacherep),
                                        0, 0, NULL);
        if (!drc_slab)
                goto out_nomem;

        drc_hashtbl = kcalloc(hashsize, sizeof(*drc_hashtbl), GFP_KERNEL);
        if (!drc_hashtbl) {
                drc_hashtbl = vzalloc(array_size(hashsize,
                                                 sizeof(*drc_hashtbl)));
                if (!drc_hashtbl)
                        goto out_nomem;
        }

        for (i = 0; i < hashsize; i++) {
                INIT_LIST_HEAD(&drc_hashtbl[i].lru_head);
                spin_lock_init(&drc_hashtbl[i].cache_lock);
        }
        drc_hashsize = hashsize;

        return 0;
out_nomem:
        printk(KERN_ERR "nfsd: failed to allocate reply cache\n");
        nfsd_reply_cache_shutdown();
        return -ENOMEM;
}

void nfsd_reply_cache_shutdown(void)
{
        struct svc_cacherep     *rp;
        unsigned int i;

        unregister_shrinker(&nfsd_reply_cache_shrinker);

        for (i = 0; i < drc_hashsize; i++) {
                struct list_head *head = &drc_hashtbl[i].lru_head;
                while (!list_empty(head)) {
                        rp = list_first_entry(head, struct svc_cacherep, c_lru);
                        nfsd_reply_cache_free_locked(rp);
                }
        }

        kvfree(drc_hashtbl);
        drc_hashtbl = NULL;
        drc_hashsize = 0;

        kmem_cache_destroy(drc_slab);
        drc_slab = NULL;
}

/*
 * Move cache entry to end of LRU list, and queue the cleaner to run if it's
 * not already scheduled.
 */
static void
lru_put_end(struct nfsd_drc_bucket *b, struct svc_cacherep *rp)
{
        rp->c_timestamp = jiffies;
        list_move_tail(&rp->c_lru, &b->lru_head);
}

static long
prune_bucket(struct nfsd_drc_bucket *b)
{
        struct svc_cacherep *rp, *tmp;
        long freed = 0;

        list_for_each_entry_safe(rp, tmp, &b->lru_head, c_lru) {
                /*
                 * Don't free entries attached to calls that are still
                 * in-progress, but do keep scanning the list.
                 */
                if (rp->c_state == RC_INPROG)
                        continue;
                if (atomic_read(&num_drc_entries) <= max_drc_entries &&
                    time_before(jiffies, rp->c_timestamp + RC_EXPIRE))
                        break;
                nfsd_reply_cache_free_locked(rp);
                freed++;
        }
        return freed;
}

/*
 * Walk the LRU list and prune off entries that are older than RC_EXPIRE.
 * Also prune the oldest ones when the total exceeds the max number of entries.
 */
static long
prune_cache_entries(void)
{
        unsigned int i;
        long freed = 0;

        for (i = 0; i < drc_hashsize; i++) {
                struct nfsd_drc_bucket *b = &drc_hashtbl[i];

                if (list_empty(&b->lru_head))
                        continue;
                spin_lock(&b->cache_lock);
                freed += prune_bucket(b);
                spin_unlock(&b->cache_lock);
        }
        return freed;
}

static unsigned long
nfsd_reply_cache_count(struct shrinker *shrink, struct shrink_control *sc)
{
        return atomic_read(&num_drc_entries);
}

static unsigned long
nfsd_reply_cache_scan(struct shrinker *shrink, struct shrink_control *sc)
{
        return prune_cache_entries();
}
/*
 * Walk an xdr_buf and get a CRC for at most the first RC_CSUMLEN bytes
 */
static __wsum
nfsd_cache_csum(struct svc_rqst *rqstp)
{
        int idx;
        unsigned int base;
        __wsum csum;
        struct xdr_buf *buf = &rqstp->rq_arg;
        const unsigned char *p = buf->head[0].iov_base;
        size_t csum_len = min_t(size_t, buf->head[0].iov_len + buf->page_len,
                                RC_CSUMLEN);
        size_t len = min(buf->head[0].iov_len, csum_len);

        /* rq_arg.head first */
        csum = csum_partial(p, len, 0);
        csum_len -= len;

        /* Continue into page array */
        idx = buf->page_base / PAGE_SIZE;
        base = buf->page_base & ~PAGE_MASK;
        while (csum_len) {
                p = page_address(buf->pages[idx]) + base;
                len = min_t(size_t, PAGE_SIZE - base, csum_len);
                csum = csum_partial(p, len, csum);
                csum_len -= len;
                base = 0;
                ++idx;
        }
        return csum;
}

static bool
nfsd_cache_match(struct svc_rqst *rqstp, __wsum csum, struct svc_cacherep *rp)
{
        /* Check RPC XID first */
        if (rqstp->rq_xid != rp->c_xid)
                return false;
        /* compare checksum of NFS data */
        if (csum != rp->c_csum) {
                ++payload_misses;
                return false;
        }

        /* Other discriminators */
        if (rqstp->rq_proc != rp->c_proc ||
            rqstp->rq_prot != rp->c_prot ||
            rqstp->rq_vers != rp->c_vers ||
            rqstp->rq_arg.len != rp->c_len ||
            !rpc_cmp_addr(svc_addr(rqstp), (struct sockaddr *)&rp->c_addr) ||
            rpc_get_port(svc_addr(rqstp)) != rpc_get_port((struct sockaddr *)&rp->c_addr))
                return false;

        return true;
}

/*
 * Search the request hash for an entry that matches the given rqstp.
 * Must be called with cache_lock held. Returns the found entry or
 * NULL on failure.
 */
static struct svc_cacherep *
nfsd_cache_search(struct nfsd_drc_bucket *b, struct svc_rqst *rqstp,
                __wsum csum)
{
        struct svc_cacherep     *rp, *ret = NULL;
        struct list_head        *rh = &b->lru_head;
        unsigned int            entries = 0;

        list_for_each_entry(rp, rh, c_lru) {
                ++entries;
                if (nfsd_cache_match(rqstp, csum, rp)) {
                        ret = rp;
                        break;
                }
        }

        /* tally hash chain length stats */
        if (entries > longest_chain) {
                longest_chain = entries;
                longest_chain_cachesize = atomic_read(&num_drc_entries);
        } else if (entries == longest_chain) {
                /* prefer to keep the smallest cachesize possible here */
                longest_chain_cachesize = min_t(unsigned int,
                                longest_chain_cachesize,
                                atomic_read(&num_drc_entries));
        }

        return ret;
}

/*
 * Try to find an entry matching the current call in the cache. When none
 * is found, we try to grab the oldest expired entry off the LRU list. If
 * a suitable one isn't there, then drop the cache_lock and allocate a
 * new one, then search again in case one got inserted while this thread
 * didn't hold the lock.
 */
int
nfsd_cache_lookup(struct svc_rqst *rqstp)
{
        struct svc_cacherep     *rp, *found;
        __be32                  xid = rqstp->rq_xid;
        u32                     proto =  rqstp->rq_prot,
                                vers = rqstp->rq_vers,
                                proc = rqstp->rq_proc;
        __wsum                  csum;
        u32 hash = nfsd_cache_hash(xid);
        struct nfsd_drc_bucket *b = &drc_hashtbl[hash];
        int type = rqstp->rq_cachetype;
        int rtn = RC_DOIT;

        rqstp->rq_cacherep = NULL;
        if (type == RC_NOCACHE) {
                nfsdstats.rcnocache++;
                return rtn;
        }

        csum = nfsd_cache_csum(rqstp);

        /*
         * Since the common case is a cache miss followed by an insert,
         * preallocate an entry.
         */
        rp = nfsd_reply_cache_alloc();
        spin_lock(&b->cache_lock);
        if (likely(rp)) {
                atomic_inc(&num_drc_entries);
                drc_mem_usage += sizeof(*rp);
        }

        /* go ahead and prune the cache */
        prune_bucket(b);

        found = nfsd_cache_search(b, rqstp, csum);
        if (found) {
                if (likely(rp))
                        nfsd_reply_cache_free_locked(rp);
                rp = found;
                goto found_entry;
        }

        if (!rp) {
                dprintk("nfsd: unable to allocate DRC entry!\n");
                goto out;
        }

        nfsdstats.rcmisses++;
        rqstp->rq_cacherep = rp;
        rp->c_state = RC_INPROG;
        rp->c_xid = xid;
        rp->c_proc = proc;
        rpc_copy_addr((struct sockaddr *)&rp->c_addr, svc_addr(rqstp));
        rpc_set_port((struct sockaddr *)&rp->c_addr, rpc_get_port(svc_addr(rqstp)));
        rp->c_prot = proto;
        rp->c_vers = vers;
        rp->c_len = rqstp->rq_arg.len;
        rp->c_csum = csum;

        lru_put_end(b, rp);

        /* release any buffer */
        if (rp->c_type == RC_REPLBUFF) {
                drc_mem_usage -= rp->c_replvec.iov_len;
                kfree(rp->c_replvec.iov_base);
                rp->c_replvec.iov_base = NULL;
        }
        rp->c_type = RC_NOCACHE;
 out:
        spin_unlock(&b->cache_lock);
        return rtn;

found_entry:
        nfsdstats.rchits++;
        /* We found a matching entry which is either in progress or done. */
        lru_put_end(b, rp);

        rtn = RC_DROPIT;
        /* Request being processed */
        if (rp->c_state == RC_INPROG)
                goto out;

        /* From the hall of fame of impractical attacks:
         * Is this a user who tries to snoop on the cache? */
        rtn = RC_DOIT;
        if (!test_bit(RQ_SECURE, &rqstp->rq_flags) && rp->c_secure)
                goto out;

        /* Compose RPC reply header */
        switch (rp->c_type) {
        case RC_NOCACHE:
                break;
        case RC_REPLSTAT:
                svc_putu32(&rqstp->rq_res.head[0], rp->c_replstat);
                rtn = RC_REPLY;
                break;
        case RC_REPLBUFF:
                if (!nfsd_cache_append(rqstp, &rp->c_replvec))
                        goto out;       /* should not happen */
                rtn = RC_REPLY;
                break;
        default:
                printk(KERN_WARNING "nfsd: bad repcache type %d\n", rp->c_type);
                nfsd_reply_cache_free_locked(rp);
        }

        goto out;
}

/*
 * Update a cache entry. This is called from nfsd_dispatch when
 * the procedure has been executed and the complete reply is in
 * rqstp->rq_res.
 *
 * We're copying around data here rather than swapping buffers because
 * the toplevel loop requires max-sized buffers, which would be a waste
 * of memory for a cache with a max reply size of 100 bytes (diropokres).
 *
 * If we should start to use different types of cache entries tailored
 * specifically for attrstat and fh's, we may save even more space.
 *
 * Also note that a cachetype of RC_NOCACHE can legally be passed when
 * nfsd failed to encode a reply that otherwise would have been cached.
 * In this case, nfsd_cache_update is called with statp == NULL.
 */
void
nfsd_cache_update(struct svc_rqst *rqstp, int cachetype, __be32 *statp)
{
        struct svc_cacherep *rp = rqstp->rq_cacherep;
        struct kvec     *resv = &rqstp->rq_res.head[0], *cachv;
        u32             hash;
        struct nfsd_drc_bucket *b;
        int             len;
        size_t          bufsize = 0;

        if (!rp)
                return;

        hash = nfsd_cache_hash(rp->c_xid);
        b = &drc_hashtbl[hash];

        len = resv->iov_len - ((char*)statp - (char*)resv->iov_base);
        len >>= 2;

        /* Don't cache excessive amounts of data and XDR failures */
        if (!statp || len > (256 >> 2)) {
                nfsd_reply_cache_free(b, rp);
                return;
        }

        switch (cachetype) {
        case RC_REPLSTAT:
                if (len != 1)
                        printk("nfsd: RC_REPLSTAT/reply len %d!\n",len);
                rp->c_replstat = *statp;
                break;
        case RC_REPLBUFF:
                cachv = &rp->c_replvec;
                bufsize = len << 2;
                cachv->iov_base = kmalloc(bufsize, GFP_KERNEL);
                if (!cachv->iov_base) {
                        nfsd_reply_cache_free(b, rp);
                        return;
                }
                cachv->iov_len = bufsize;
                memcpy(cachv->iov_base, statp, bufsize);
                break;
        case RC_NOCACHE:
                nfsd_reply_cache_free(b, rp);
                return;
        }
        spin_lock(&b->cache_lock);
        drc_mem_usage += bufsize;
        lru_put_end(b, rp);
        rp->c_secure = test_bit(RQ_SECURE, &rqstp->rq_flags);
        rp->c_type = cachetype;
        rp->c_state = RC_DONE;
        spin_unlock(&b->cache_lock);
        return;
}

/*
 * Copy cached reply to current reply buffer. Should always fit.
 * FIXME as reply is in a page, we should just attach the page, and
 * keep a refcount....
 */
static int
nfsd_cache_append(struct svc_rqst *rqstp, struct kvec *data)
{
        struct kvec     *vec = &rqstp->rq_res.head[0];

        if (vec->iov_len + data->iov_len > PAGE_SIZE) {
                printk(KERN_WARNING "nfsd: cached reply too large (%zd).\n",
                                data->iov_len);
                return 0;
        }
        memcpy((char*)vec->iov_base + vec->iov_len, data->iov_base, data->iov_len);
        vec->iov_len += data->iov_len;
        return 1;
}

/*
 * Note that fields may be added, removed or reordered in the future. Programs
 * scraping this file for info should test the labels to ensure they're
 * getting the correct field.
 */
static int nfsd_reply_cache_stats_show(struct seq_file *m, void *v)
{
        seq_printf(m, "max entries:           %u\n", max_drc_entries);
        seq_printf(m, "num entries:           %u\n",
                        atomic_read(&num_drc_entries));
        seq_printf(m, "hash buckets:          %u\n", 1 << maskbits);
        seq_printf(m, "mem usage:             %u\n", drc_mem_usage);
        seq_printf(m, "cache hits:            %u\n", nfsdstats.rchits);
        seq_printf(m, "cache misses:          %u\n", nfsdstats.rcmisses);
        seq_printf(m, "not cached:            %u\n", nfsdstats.rcnocache);
        seq_printf(m, "payload misses:        %u\n", payload_misses);
        seq_printf(m, "longest chain len:     %u\n", longest_chain);
        seq_printf(m, "cachesize at longest:  %u\n", longest_chain_cachesize);
        return 0;
}

int nfsd_reply_cache_stats_open(struct inode *inode, struct file *file)
{
        return single_open(file, nfsd_reply_cache_stats_show, NULL);
}