From 2c3c1048746a4622d8c89a29670120dc8fab93c4 Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Sun, 7 Apr 2024 20:49:45 +0200 Subject: Adding upstream version 6.1.76. Signed-off-by: Daniel Baumann --- mm/shuffle.c | 182 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 182 insertions(+) create mode 100644 mm/shuffle.c (limited to 'mm/shuffle.c') diff --git a/mm/shuffle.c b/mm/shuffle.c new file mode 100644 index 000000000..fb1393b8b --- /dev/null +++ b/mm/shuffle.c @@ -0,0 +1,182 @@ +// SPDX-License-Identifier: GPL-2.0 +// Copyright(c) 2018 Intel Corporation. All rights reserved. + +#include +#include +#include +#include +#include +#include "internal.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 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; +} -- cgit v1.2.3