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mm: add a signature in struct page

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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: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Matteo Croce <mcroce@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Matteo Croce 2021-06-07 21:02:36 +02:00 committed by David S. Miller
parent 35cba15a50
commit c07aea3ef4
4 changed files with 22 additions and 5 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

11
include/linux/mm.h
View file

@ -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;
}
/*

7
include/linux/mm_types.h
View file

@ -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.

3
include/linux/poison.h
View file

@ -78,4 +78,7 @@
/********** security/ **********/
#define KEY_DESTROY 0xbd
/********** net/core/page_pool.c **********/
#define PP_SIGNATURE (0x40 + POISON_POINTER_DELTA)
#endif

6
net/core/page_pool.c
View file

@ -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.
*/