Commit c07aea3e authored by Matteo Croce's avatar Matteo Croce Committed by David S. Miller
Browse files

mm: add a signature in struct page 



This is needed by the page_pool to avoid recycling a page not allocated
via page_pool.

The page->signature field is aliased to page->lru.next and
page->compound_head, but it can't be set by mistake because the
signature value is a bad pointer, and can't trigger a false positive
in PageTail() because the last bit is 0.

Co-developed-by: default avatarMatthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: default avatarMatthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: default avatarMatteo Croce <mcroce@microsoft.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 35cba15a

include/linux/mm.h

+6 −5
Original line number Diff line number Diff line
@@ -1668,10 +1668,11 @@ struct address_space *page_mapping(struct page *page); 
static inline bool page_is_pfmemalloc(const struct page *page)

{

	/*

	 * Page index cannot be this large so this must be

	 * a pfmemalloc page.

	 * lru.next has bit 1 set if the page is allocated from the

	 * pfmemalloc reserves.  Callers may simply overwrite it if

	 * they do not need to preserve that information.

	 */

	return page->index == -1UL;

	return (uintptr_t)page->lru.next & BIT(1);

}



/*
@@ -1680,12 +1681,12 @@ static inline bool page_is_pfmemalloc(const struct page *page) 
 */

static inline void set_page_pfmemalloc(struct page *page)

{

	page->index = -1UL;

	page->lru.next = (void *)BIT(1);

}



static inline void clear_page_pfmemalloc(struct page *page)

{

	page->index = 0;

	page->lru.next = NULL;

}



/*

include/linux/mm_types.h

+7 −0
Original line number Diff line number Diff line
@@ -96,6 +96,13 @@ struct page { 
			unsigned long private;

		};

		struct {	/* page_pool used by netstack */

			/**

			 * @pp_magic: magic value to avoid recycling non

			 * page_pool allocated pages.

			 */

			unsigned long pp_magic;

			struct page_pool *pp;

			unsigned long _pp_mapping_pad;

			/**

			 * @dma_addr: might require a 64-bit value on

			 * 32-bit architectures.

include/linux/poison.h

+3 −0
Original line number Diff line number Diff line
@@ -78,4 +78,7 @@ 
/********** security/ **********/

#define KEY_DESTROY		0xbd



/********** net/core/page_pool.c **********/

#define PP_SIGNATURE		(0x40 + POISON_POINTER_DELTA)



#endif

net/core/page_pool.c

+6 −0
Original line number Diff line number Diff line
@@ -17,6 +17,7 @@ 
#include <linux/dma-mapping.h>

#include <linux/page-flags.h>

#include <linux/mm.h> /* for __put_page() */

#include <linux/poison.h>



#include <trace/events/page_pool.h>
@@ -221,6 +222,8 @@ static struct page *__page_pool_alloc_page_order(struct page_pool *pool, 
		return NULL;

	}



	page->pp_magic |= PP_SIGNATURE;



	/* Track how many pages are held 'in-flight' */

	pool->pages_state_hold_cnt++;

	trace_page_pool_state_hold(pool, page, pool->pages_state_hold_cnt);
@@ -263,6 +266,7 @@ static struct page *__page_pool_alloc_pages_slow(struct page_pool *pool, 
			put_page(page);

			continue;

		}

		page->pp_magic |= PP_SIGNATURE;

		pool->alloc.cache[pool->alloc.count++] = page;

		/* Track how many pages are held 'in-flight' */

		pool->pages_state_hold_cnt++;
@@ -341,6 +345,8 @@ void page_pool_release_page(struct page_pool *pool, struct page *page) 
			     DMA_ATTR_SKIP_CPU_SYNC);

	page_pool_set_dma_addr(page, 0);

skip_dma_unmap:

	page->pp_magic = 0;



	/* This may be the last page returned, releasing the pool, so

	 * it is not safe to reference pool afterwards.

	 */