Plan 9 Resource Sharing for Linux v9fs

#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/page-debug-flags.h>
#include <linux/poison.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_highpage(struct page *page)
{
	/*
	 * Page poisoning for highmem pages is not implemented.
	 *
	 * This can be called from interrupt contexts.
	 * So we need to create a new kmap_atomic slot for this
	 * application and it will need interrupt protection.
	 */
}

static void poison_page(struct page *page)
{
	void *addr;

	if (PageHighMem(page)) {
		poison_highpage(page);
		return;
	}
	set_page_poison(page);
	addr = page_address(page);
	memset(addr, PAGE_POISON, PAGE_SIZE);
}

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)
{
	unsigned char *start;
	unsigned char *end;

	for (start = mem; start < mem + bytes; start++) {
		if (*start != PAGE_POISON)
			break;
	}
	if (start == mem + bytes)
		return;

	for (end = mem + bytes - 1; end > start; end--) {
		if (*end != PAGE_POISON)
			break;
	}

	if (!printk_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_highpage(struct page *page)
{
	/*
	 * See comment in poison_highpage().
	 * Highmem pages should not be poisoned for now
	 */
	BUG_ON(page_poison(page));
}

static void unpoison_page(struct page *page)
{
	if (PageHighMem(page)) {
		unpoison_highpage(page);
		return;
	}
	if (page_poison(page)) {
		void *addr = page_address(page);

		check_poison_mem(addr, PAGE_SIZE);
		clear_page_poison(page);
	}
}

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);
}