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(I'm so sorry!) Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel os linux
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123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159160161162163164165166167168169170171172173174175176177178179180181182183184// 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 "page_alloc.h"#include "shuffle.h"
DEFINE_STATIC_KEY_FALSE(page_alloc_shuffle_key);
static bool shuffle_param;
static __meminit int shuffle_param_set(const char *val, const struct kernel_param *kp){ if (param_set_bool(val, kp)) return -EINVAL; if (*(bool *)kp->arg) static_branch_enable(&page_alloc_shuffle_key); return 0;}
static const struct kernel_param_ops shuffle_param_ops = { .set = shuffle_param_set, .get = param_get_bool,};module_param_cb(shuffle, &shuffle_param_ops, &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 10void __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;}