// SPDX-License-Identifier: GPL-2.0
/* IPVS: Maglev Hashing scheduling module
*
* Authors: Inju Song <[email protected]>
*
*/
/* The mh algorithm is to assign a preference list of all the lookup
* table positions to each destination and populate the table with
* the most-preferred position of destinations. Then it is to select
* destination with the hash key of source IP address through looking
* up a the lookup table.
*
* The algorithm is detailed in:
* [3.4 Consistent Hasing]
https://www.usenix.org/system/files/conference/nsdi16/nsdi16-paper-eisenbud.pdf
*
*/
#define KMSG_COMPONENT "IPVS"
#define pr_fmt(fmt) KMSG_COMPONENT ": " fmt
#include <linux/ip.h>
#include <linux/slab.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/skbuff.h>
#include <net/ip_vs.h>
#include <linux/siphash.h>
#include <linux/bitops.h>
#include <linux/gcd.h>
#define IP_VS_SVC_F_SCHED_MH_FALLBACK IP_VS_SVC_F_SCHED1 /* MH fallback */
#define IP_VS_SVC_F_SCHED_MH_PORT IP_VS_SVC_F_SCHED2 /* MH use port */
struct ip_vs_mh_lookup {
struct ip_vs_dest __rcu *dest; /* real server (cache) */
};
struct ip_vs_mh_dest_setup {
unsigned int offset; /* starting offset */
unsigned int skip; /* skip */
unsigned int perm; /* next_offset */
int turns; /* weight / gcd() and rshift */
};
/* Available prime numbers for MH table */
static int primes[] = {251, 509, 1021, 2039, 4093,
8191, 16381, 32749, 65521, 131071};
/* For IPVS MH entry hash table */
#ifndef CONFIG_IP_VS_MH_TAB_INDEX
#define CONFIG_IP_VS_MH_TAB_INDEX 12
#endif
#define IP_VS_MH_TAB_BITS (CONFIG_IP_VS_MH_TAB_INDEX / 2)
#define IP_VS_MH_TAB_INDEX (CONFIG_IP_VS_MH_TAB_INDEX - 8)
#define IP_VS_MH_TAB_SIZE primes[IP_VS_MH_TAB_INDEX]
struct ip_vs_mh_state {
struct rcu_head rcu_head;
struct ip_vs_mh_lookup *lookup;
struct ip_vs_mh_dest_setup *dest_setup;
hsiphash_key_t hash1, hash2;
int gcd;
int rshift;
};
static inline void generate_hash_secret(hsiphash_key_t *hash1,
hsiphash_key_t *hash2)
{
hash1->key[0] = 2654435761UL;
hash1->key[1] = 2654435761UL;
hash2->key[0] = 2654446892UL;
hash2->key[1] = 2654446892UL;
}
/* Helper function to determine if server is unavailable */
static inline bool is_unavailable(struct ip_vs_dest *dest)
{
return atomic_read(&dest->weight) <= 0 ||
dest->flags & IP_VS_DEST_F_OVERLOAD;
}
/* Returns hash value for IPVS MH entry */
static inline unsigned int
ip_vs_mh_hashkey(int af, const union nf_inet_addr *addr,
__be16 port, hsiphash_key_t *key, unsigned int offset)
{
unsigned int v;
__be32 addr_fold = addr->ip;
#ifdef CONFIG_IP_VS_IPV6
if (af == AF_INET6)
addr_fold = addr->ip6[0] ^ addr->ip6[1] ^
addr->ip6[2] ^ addr->ip6[3];
#endif
v = (offset + ntohs(port) + ntohl(addr_fold));
return hsiphash(&v, sizeof(v), key);
}
/* Reset all the hash buckets of the specified table. */
static void ip_vs_mh_reset(struct ip_vs_mh_state *s)
{
int i;
struct ip_vs_mh_lookup *l;
struct ip_vs_dest *dest;
l = &s->lookup[0];
for (i = 0; i < IP_VS_MH_TAB_SIZE; i++) {
dest = rcu_dereference_protected(l->dest, 1);
if (dest) {
ip_vs_dest_put(dest);
RCU_INIT_POINTER(l->dest, NULL);
}
l++;
}
}
static int ip_vs_mh_permutate(struct ip_vs_mh_state *s,
struct ip_vs_service *svc)
{
struct list_head *p;
struct ip_vs_mh_dest_setup *ds;
struct ip_vs_dest *dest;
int lw;
/* If gcd is smaller then 1, number of dests or
* all last_weight of dests are zero. So, skip
* permutation for the dests.
*/
if (s->gcd < 1)
return 0;
/* Set dest_setup for the dests permutation */
p = &svc->destinations;
ds = &s->dest_setup[0];
while ((p = p->next) != &svc->destinations) {
dest = list_entry(p, struct ip_vs_dest, n_list);
ds->offset = ip_vs_mh_hashkey(svc->af, &dest->addr,
dest->port, &s->hash1, 0) %
IP_VS_MH_TAB_SIZE;
ds->skip = ip_vs_mh_hashkey(svc->af, &dest->addr,
dest->port, &s->hash2, 0) %
(IP_VS_MH_TAB_SIZE - 1) + 1;
ds->perm = ds->offset;
lw = atomic_read(&dest->last_weight);
ds->turns = ((lw / s->gcd) >> s->rshift) ? : (lw != 0);
ds++;
}
return 0;
}
static int ip_vs_mh_populate(struct ip_vs_mh_state *s,
struct ip_vs_service *svc)
{
int n, c, dt_count;
unsigned long *table;
struct list_head *p;
struct ip_vs_mh_dest_setup *ds;
struct ip_vs_dest *dest, *new_dest;
/* If gcd is smaller then 1, number of dests or
* all last_weight of dests are zero. So, skip
* the population for the dests and reset lookup table.
*/
if (s->gcd < 1) {
ip_vs_mh_reset(s);
return 0;
}
table = bitmap_zalloc(IP_VS_MH_TAB_SIZE, GFP_KERNEL);
if (!table)
return -ENOMEM;
p = &svc->destinations;
n = 0;
dt_count = 0;
while (n < IP_VS_MH_TAB_SIZE) {
if (p == &svc->destinations)
p = p->next;
ds = &s->dest_setup[0];
while (p != &svc->destinations) {
/* Ignore added server with zero weight */
if (ds->turns < 1) {
p = p->next;
ds++;
continue;
}
c = ds->perm;
while (test_bit(c, table)) {
/* Add skip, mod IP_VS_MH_TAB_SIZE */
ds->perm += ds->skip;
if (ds->perm >= IP_VS_MH_TAB_SIZE)
ds->perm -= IP_VS_MH_TAB_SIZE;
c = ds->perm;
}
__set_bit(c, table);
dest = rcu_dereference_protected(s->lookup[c].dest, 1);
new_dest = list_entry(p, struct ip_vs_dest, n_list);
if (dest != new_dest) {
if (dest)
ip_vs_dest_put(dest);
ip_vs_dest_hold(new_dest);
RCU_INIT_POINTER(s->lookup[c].dest, new_dest);
}
if (++n == IP_VS_MH_TAB_SIZE)
goto out;
if (++dt_count >= ds->turns) {
dt_count = 0;
p = p->next;
ds++;
}
}
}
out:
bitmap_free(table);
return 0;
}
/* Get ip_vs_dest associated with supplied parameters. */
static inline struct ip_vs_dest *
ip_vs_mh_get(struct ip_vs_service *svc, struct ip_vs_mh_state *s,
const union nf_inet_addr *addr, __be16 port)
{
unsigned int hash = ip_vs_mh_hashkey(svc->af, addr, port, &s->hash1, 0)
% IP_VS_MH_TAB_SIZE;
struct ip_vs_dest *dest = rcu_dereference(s->lookup[hash].dest);
return (!dest || is_unavailable(dest)) ? NULL : dest;
}
/* As ip_vs_mh_get, but with fallback if selected server is unavailable */
static inline struct ip_vs_dest *
ip_vs_mh_get_fallback(struct ip_vs_service *svc, struct ip_vs_mh_state *s,
const union nf_inet_addr *addr, __be16 port)
{
unsigned int offset, roffset;
unsigned int hash, ihash;
struct ip_vs_dest *dest;
/* First try the dest it's supposed to go to */
ihash = ip_vs_mh_hashkey(svc->af, addr, port,
&s->hash1, 0) % IP_VS_MH_TAB_SIZE;
dest = rcu_dereference(s->lookup[ihash].dest);
if (!dest)
return NULL;
if (!is_unavailable(dest))
return dest;
IP_VS_DBG_BUF(6, "MH: selected unavailable server %s:%u, reselecting",
IP_VS_DBG_ADDR(dest->af, &dest->addr), ntohs(dest->port));
/* If the original dest is unavailable, loop around the table
* starting from ihash to find a new dest
*/
for (offset = 0; offset < IP_VS_MH_TAB_SIZE; offset++) {
roffset = (offset + ihash) % IP_VS_MH_TAB_SIZE;
hash = ip_vs_mh_hashkey(svc->af, addr, port, &s->hash1,
roffset) % IP_VS_MH_TAB_SIZE;
dest = rcu_dereference(s->lookup[hash].dest);
if (!dest)
break;
if (!is_unavailable(dest))
return dest;
IP_VS_DBG_BUF(6,
"MH: selected unavailable server %s:%u (offset %u), reselecting",
IP_VS_DBG_ADDR(dest->af, &dest->addr),
ntohs(dest->port), roffset);
}
return NULL;
}
/* Assign all the hash buckets of the specified table with the service. */
static int ip_vs_mh_reassign(struct ip_vs_mh_state *s,
struct ip_vs_service *svc)
{
int ret;
if (svc->num_dests > IP_VS_MH_TAB_SIZE)
return -EINVAL;
if (svc->num_dests >= 1) {
s->dest_setup = kcalloc(svc->num_dests,
sizeof(struct ip_vs_mh_dest_setup),
GFP_KERNEL);
if (!s->dest_setup)
return -ENOMEM;
}
ip_vs_mh_permutate(s, svc);
ret = ip_vs_mh_populate(s, svc);
if (ret < 0)
goto out;
IP_VS_DBG_BUF(6, "MH: reassign lookup table of %s:%u\n",
IP_VS_DBG_ADDR(svc->af, &svc->addr),
ntohs(svc->port));
out:
if (svc->num_dests >= 1) {
kfree(s->dest_setup);
s->dest_setup = NULL;
}
return ret;
}
static int ip_vs_mh_gcd_weight(struct ip_vs_service *svc)
{
struct ip_vs_dest *dest;
int weight;
int g = 0;
list_for_each_entry(dest, &svc->destinations, n_list) {
weight = atomic_read(&dest->last_weight);
if (weight > 0) {
if (g > 0)
g = gcd(weight, g);
else
g = weight;
}
}
return g;
}
/* To avoid assigning huge weight for the MH table,
* calculate shift value with gcd.
*/
static int ip_vs_mh_shift_weight(struct ip_vs_service *svc, int gcd)
{
struct ip_vs_dest *dest;
int new_weight, weight = 0;
int mw, shift;
/* If gcd is smaller then 1, number of dests or
* all last_weight of dests are zero. So, return
* shift value as zero.
*/
if (gcd < 1)
return 0;
list_for_each_entry(dest, &svc->destinations, n_list) {
new_weight = atomic_read(&dest->last_weight);
if (new_weight > weight)
weight = new_weight;
}
/* Because gcd is greater than zero,
* the maximum weight and gcd are always greater than zero
*/
mw = weight / gcd;
/* shift = occupied bits of weight/gcd - MH highest bits */
shift = fls(mw) - IP_VS_MH_TAB_BITS;
return (shift >= 0) ? shift : 0;
}
static void ip_vs_mh_state_free(struct rcu_head *head)
{
struct ip_vs_mh_state *s;
s = container_of(head, struct ip_vs_mh_state, rcu_head);
kfree(s->lookup);
kfree(s);
}
static int ip_vs_mh_init_svc(struct ip_vs_service *svc)
{
int ret;
struct ip_vs_mh_state *s;
/* Allocate the MH table for this service */
s = kzalloc(sizeof(*s), GFP_KERNEL);
if (!s)
return -ENOMEM;
s->lookup = kcalloc(IP_VS_MH_TAB_SIZE, sizeof(struct ip_vs_mh_lookup),
GFP_KERNEL);
if (!s->lookup) {
kfree(s);
return -ENOMEM;
}
generate_hash_secret(&s->hash1, &s->hash2);
s->gcd = ip_vs_mh_gcd_weight(svc);
s->rshift = ip_vs_mh_shift_weight(svc, s->gcd);
IP_VS_DBG(6,
"MH lookup table (memory=%zdbytes) allocated for current service\n",
sizeof(struct ip_vs_mh_lookup) * IP_VS_MH_TAB_SIZE);
/* Assign the lookup table with current dests */
ret = ip_vs_mh_reassign(s, svc);
if (ret < 0) {
ip_vs_mh_reset(s);
ip_vs_mh_state_free(&s->rcu_head);
return ret;
}
/* No more failures, attach state */
svc->sched_data = s;
return 0;
}
static void ip_vs_mh_done_svc(struct ip_vs_service *svc)
{
struct ip_vs_mh_state *s = svc->sched_data;
/* Got to clean up lookup entry here */
ip_vs_mh_reset(s);
call_rcu(&s->rcu_head, ip_vs_mh_state_free);
IP_VS_DBG(6, "MH lookup table (memory=%zdbytes) released\n",
sizeof(struct ip_vs_mh_lookup) * IP_VS_MH_TAB_SIZE);
}
static int ip_vs_mh_dest_changed(struct ip_vs_service *svc,
struct ip_vs_dest *dest)
{
struct ip_vs_mh_state *s = svc->sched_data;
s->gcd = ip_vs_mh_gcd_weight(svc);
s->rshift = ip_vs_mh_shift_weight(svc, s->gcd);
/* Assign the lookup table with the updated service */
return ip_vs_mh_reassign(s, svc);
}
/* Helper function to get port number */
static inline __be16
ip_vs_mh_get_port(const struct sk_buff *skb, struct ip_vs_iphdr *iph)
{
__be16 _ports[2], *ports;
/* At this point we know that we have a valid packet of some kind.
* Because ICMP packets are only guaranteed to have the first 8
* bytes, let's just grab the ports. Fortunately they're in the
* same position for all three of the protocols we care about.
*/
switch (iph->protocol) {
case IPPROTO_TCP:
case IPPROTO_UDP:
case IPPROTO_SCTP:
ports = skb_header_pointer(skb, iph->len, sizeof(_ports),
&_ports);
if (unlikely(!ports))
return 0;
if (likely(!ip_vs_iph_inverse(iph)))
return ports[0];
else
return ports[1];
default:
return 0;
}
}
/* Maglev Hashing scheduling */
static struct ip_vs_dest *
ip_vs_mh_schedule(struct ip_vs_service *svc, const struct sk_buff *skb,
struct ip_vs_iphdr *iph)
{
struct ip_vs_dest *dest;
struct ip_vs_mh_state *s;
__be16 port = 0;
const union nf_inet_addr *hash_addr;
hash_addr = ip_vs_iph_inverse(iph) ? &iph->daddr : &iph->saddr;
IP_VS_DBG(6, "%s : Scheduling...\n", __func__);
if (svc->flags & IP_VS_SVC_F_SCHED_MH_PORT)
port = ip_vs_mh_get_port(skb, iph);
s = (struct ip_vs_mh_state *)svc->sched_data;
if (svc->flags & IP_VS_SVC_F_SCHED_MH_FALLBACK)
dest = ip_vs_mh_get_fallback(svc, s, hash_addr, port);
else
dest = ip_vs_mh_get(svc, s, hash_addr, port);
if (!dest) {
ip_vs_scheduler_err(svc, "no destination available");
return NULL;
}
IP_VS_DBG_BUF(6, "MH: source IP address %s:%u --> server %s:%u\n",
IP_VS_DBG_ADDR(svc->af, hash_addr),
ntohs(port),
IP_VS_DBG_ADDR(dest->af, &dest->addr),
ntohs(dest->port));
return dest;
}
/* IPVS MH Scheduler structure */
static struct ip_vs_scheduler ip_vs_mh_scheduler = {
.name = "mh",
.refcnt = ATOMIC_INIT(0),
.module = THIS_MODULE,
.n_list = LIST_HEAD_INIT(ip_vs_mh_scheduler.n_list),
.init_service = ip_vs_mh_init_svc,
.done_service = ip_vs_mh_done_svc,
.add_dest = ip_vs_mh_dest_changed,
.del_dest = ip_vs_mh_dest_changed,
.upd_dest = ip_vs_mh_dest_changed,
.schedule = ip_vs_mh_schedule,
};
static int __init ip_vs_mh_init(void)
{
return register_ip_vs_scheduler(&ip_vs_mh_scheduler);
}
static void __exit ip_vs_mh_cleanup(void)
{
unregister_ip_vs_scheduler(&ip_vs_mh_scheduler);
rcu_barrier();
}
module_init(ip_vs_mh_init);
module_exit(ip_vs_mh_cleanup);
MODULE_DESCRIPTION("Maglev hashing ipvs scheduler");
MODULE_LICENSE("GPL v2");
MODULE_AUTHOR("Inju Song <[email protected]>");
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