#include <linux/kernel.h>#include <linux/string.h>#include <linux/mm.h>#include <linux/highmem.h>#include <linux/page-debug-flags.h>#include <linux/poison.h>#include <linux/ratelimit.h> static inline void set_page_poison(struct page *page){	__set_bit(PAGE_DEBUG_FLAG_POISON, &page->debug_flags);} static inline void clear_page_poison(struct page *page){	__clear_bit(PAGE_DEBUG_FLAG_POISON, &page->debug_flags);} static inline bool page_poison(struct page *page){	return test_bit(PAGE_DEBUG_FLAG_POISON, &page->debug_flags);} static void poison_page(struct page *page){	void *addr = kmap_atomic(page); 	set_page_poison(page);	memset(addr, PAGE_POISON, PAGE_SIZE);	kunmap_atomic(addr);} static void poison_pages(struct page *page, int n){	int i; 	for (i = 0; i < n; i++)		poison_page(page + i);} static bool single_bit_flip(unsigned char a, unsigned char b){	unsigned char error = a ^ b; 	return error && !(error & (error - 1));} static void check_poison_mem(unsigned char *mem, size_t bytes){	static DEFINE_RATELIMIT_STATE(ratelimit, 5 * HZ, 10);	unsigned char *start;	unsigned char *end; 	start = memchr_inv(mem, PAGE_POISON, bytes);	if (!start)		return; 	for (end = mem + bytes - 1; end > start; end--) {		if (*end != PAGE_POISON)			break;	} 	if (!__ratelimit(&ratelimit))		return;	else if (start == end && single_bit_flip(*start, PAGE_POISON))		printk(KERN_ERR "pagealloc: single bit error\n");	else		printk(KERN_ERR "pagealloc: memory corruption\n"); 	print_hex_dump(KERN_ERR, "", DUMP_PREFIX_ADDRESS, 16, 1, start,			end - start + 1, 1);	dump_stack();} static void unpoison_page(struct page *page){	void *addr; 	if (!page_poison(page))		return; 	addr = kmap_atomic(page);	check_poison_mem(addr, PAGE_SIZE);	clear_page_poison(page);	kunmap_atomic(addr);} static void unpoison_pages(struct page *page, int n){	int i; 	for (i = 0; i < n; i++)		unpoison_page(page + i);} void kernel_map_pages(struct page *page, int numpages, int enable){	if (!debug_pagealloc_enabled)		return; 	if (enable)		unpoison_pages(page, numpages);	else		poison_pages(page, numpages);}