forked from Qortal/Brooklyn
You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
183 lines
4.7 KiB
183 lines
4.7 KiB
// 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" |
|
|
|
DEFINE_STATIC_KEY_FALSE(page_alloc_shuffle_key); |
|
|
|
static bool shuffle_param; |
|
static int shuffle_show(char *buffer, const struct kernel_param *kp) |
|
{ |
|
return sprintf(buffer, "%c\n", shuffle_param ? '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) |
|
static_branch_enable(&page_alloc_shuffle_key); |
|
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; |
|
|
|
/* ...is the page free and currently on a free_area list? */ |
|
if (!PageBuddy(page)) |
|
return NULL; |
|
|
|
/* |
|
* ...is the page on the same list as the page we will |
|
* shuffle it with? |
|
*/ |
|
if (buddy_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) |
|
continue; |
|
|
|
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, |
|
order_pages); |
|
page_j = shuffle_valid_page(z, j, order); |
|
if (page_j && page_j != page_i) |
|
break; |
|
} |
|
if (retry >= SHUFFLE_RETRY) { |
|
pr_debug("%s: failed to swap %#lx\n", __func__, i); |
|
continue; |
|
} |
|
|
|
/* |
|
* 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); |
|
continue; |
|
} |
|
|
|
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); |
|
cond_resched(); |
|
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++) |
|
shuffle_zone(z); |
|
} |
|
|
|
bool shuffle_pick_tail(void) |
|
{ |
|
static u64 rand; |
|
static u8 rand_bits; |
|
bool ret; |
|
|
|
/* |
|
* 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(); |
|
} |
|
|
|
ret = rand & 1; |
|
|
|
rand_bits--; |
|
rand >>= 1; |
|
|
|
return ret; |
|
}
|
|
|