blob: 56958ffa5a3a9c242c26d363845020599946c7aa [file] [log] [blame]
// SPDX-License-Identifier: GPL-2.0
// Copyright(c) 2018 Intel Corporation. All rights reserved.
#include <linux/mm.h>
#include <linux/init.h>
#include <linux/mmzone.h>
#include <linux/random.h>
#include <linux/moduleparam.h>
#include "internal.h"
#include "shuffle.h"
static unsigned long shuffle_state __ro_after_init;
* Depending on the architecture, module parameter parsing may run
* before, or after the cache detection. SHUFFLE_FORCE_DISABLE prevents,
* or reverts the enabling of the shuffle implementation. SHUFFLE_ENABLE
* attempts to turn on the implementation, but aborts if it finds
__meminit void page_alloc_shuffle(enum mm_shuffle_ctl ctl)
set_bit(SHUFFLE_FORCE_DISABLE, &shuffle_state);
if (test_bit(SHUFFLE_FORCE_DISABLE, &shuffle_state)) {
if (test_and_clear_bit(SHUFFLE_ENABLE, &shuffle_state))
} else if (ctl == SHUFFLE_ENABLE
&& !test_and_set_bit(SHUFFLE_ENABLE, &shuffle_state))
static bool shuffle_param;
static int shuffle_show(char *buffer, const struct kernel_param *kp)
return sprintf(buffer, "%c\n", test_bit(SHUFFLE_ENABLE, &shuffle_state)
? 'Y' : 'N');
static __meminit int shuffle_store(const char *val,
const struct kernel_param *kp)
int rc = param_set_bool(val, kp);
if (rc < 0)
return rc;
if (shuffle_param)
return 0;
module_param_call(shuffle, shuffle_store, shuffle_show, &shuffle_param, 0400);
* For two pages to be swapped in the shuffle, they must be free (on a
* 'free_area' lru), have the same order, and have the same migratetype.
static struct page * __meminit shuffle_valid_page(struct zone *zone,
unsigned long pfn, int order)
struct page *page = pfn_to_online_page(pfn);
* Given we're dealing with randomly selected pfns in a zone we
* need to ask questions like...
/* ... is the page managed by the buddy? */
if (!page)
return NULL;
/* ... is the page assigned to the same zone? */
if (page_zone(page) != zone)
return NULL;
/* the page free and currently on a free_area list? */
if (!PageBuddy(page))
return NULL;
* the page on the same list as the page we will
* shuffle it with?
if (page_order(page) != order)
return NULL;
return page;
* Fisher-Yates shuffle the freelist which prescribes iterating through an
* array, pfns in this case, and randomly swapping each entry with another in
* the span, end_pfn - start_pfn.
* To keep the implementation simple it does not attempt to correct for sources
* of bias in the distribution, like modulo bias or pseudo-random number
* generator bias. I.e. the expectation is that this shuffling raises the bar
* for attacks that exploit the predictability of page allocations, but need not
* be a perfect shuffle.
#define SHUFFLE_RETRY 10
void __meminit __shuffle_zone(struct zone *z)
unsigned long i, flags;
unsigned long start_pfn = z->zone_start_pfn;
unsigned long end_pfn = zone_end_pfn(z);
const int order = SHUFFLE_ORDER;
const int order_pages = 1 << order;
spin_lock_irqsave(&z->lock, flags);
start_pfn = ALIGN(start_pfn, order_pages);
for (i = start_pfn; i < end_pfn; i += order_pages) {
unsigned long j;
int migratetype, retry;
struct page *page_i, *page_j;
* We expect page_i, in the sub-range of a zone being added
* (@start_pfn to @end_pfn), to more likely be valid compared to
* page_j randomly selected in the span @zone_start_pfn to
* @spanned_pages.
page_i = shuffle_valid_page(z, i, order);
if (!page_i)
for (retry = 0; retry < SHUFFLE_RETRY; retry++) {
* Pick a random order aligned page in the zone span as
* a swap target. If the selected pfn is a hole, retry
* up to SHUFFLE_RETRY attempts find a random valid pfn
* in the zone.
j = z->zone_start_pfn +
ALIGN_DOWN(get_random_long() % z->spanned_pages,
page_j = shuffle_valid_page(z, j, order);
if (page_j && page_j != page_i)
if (retry >= SHUFFLE_RETRY) {
pr_debug("%s: failed to swap %#lx\n", __func__, i);
* Each migratetype corresponds to its own list, make sure the
* types match otherwise we're moving pages to lists where they
* do not belong.
migratetype = get_pageblock_migratetype(page_i);
if (get_pageblock_migratetype(page_j) != migratetype) {
pr_debug("%s: migratetype mismatch %#lx\n", __func__, i);
list_swap(&page_i->lru, &page_j->lru);
pr_debug("%s: swap: %#lx -> %#lx\n", __func__, i, j);
/* take it easy on the zone lock */
if ((i % (100 * order_pages)) == 0) {
spin_unlock_irqrestore(&z->lock, flags);
spin_lock_irqsave(&z->lock, flags);
spin_unlock_irqrestore(&z->lock, flags);
* shuffle_free_memory - reduce the predictability of the page allocator
* @pgdat: node page data
void __meminit __shuffle_free_memory(pg_data_t *pgdat)
struct zone *z;
for (z = pgdat->node_zones; z < pgdat->node_zones + MAX_NR_ZONES; z++)
void add_to_free_area_random(struct page *page, struct free_area *area,
int migratetype)
static u64 rand;
static u8 rand_bits;
* The lack of locking is deliberate. If 2 threads race to
* update the rand state it just adds to the entropy.
if (rand_bits == 0) {
rand_bits = 64;
rand = get_random_u64();
if (rand & 1)
add_to_free_area(page, area, migratetype);
add_to_free_area_tail(page, area, migratetype);
rand >>= 1;