// 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;}