Re: [PATCH 1/1] mm: Fix struct page layout on 32-bit systems
From: Matthew Wilcox <willy@infradead.org>
Date: 2021-04-14 21:36:19
Also in:
linux-mips, linux-mm, linuxppc-dev, lkml, netdev
On Wed, Apr 14, 2021 at 09:13:22PM +0200, Jesper Dangaard Brouer wrote:
(If others want to reproduce). First I could not reproduce on ARM32. Then I found out that enabling CONFIG_XEN on ARCH=arm was needed to cause the issue by enabling CONFIG_ARCH_DMA_ADDR_T_64BIT.
hmmm ... you should be able to provoke it by enabling ARM_LPAE,
which selects PHYS_ADDR_T_64BIT, and
config ARCH_DMA_ADDR_T_64BIT
def_bool 64BIT || PHYS_ADDR_T_64BIT
struct page {
long unsigned int flags; /* 0 4 */
/* XXX 4 bytes hole, try to pack */
union {
struct {
struct list_head lru; /* 8 8 */
struct address_space * mapping; /* 16 4 */
long unsigned int index; /* 20 4 */
long unsigned int private; /* 24 4 */
}; /* 8 20 */
struct {
dma_addr_t dma_addr; /* 8 8 */
}; /* 8 8 */[...]
} __attribute__((__aligned__(8))); /* 8 24 */
union {
atomic_t _mapcount; /* 32 4 */
unsigned int page_type; /* 32 4 */
unsigned int active; /* 32 4 */
int units; /* 32 4 */
}; /* 32 4 */
atomic_t _refcount; /* 36 4 */
/* size: 40, cachelines: 1, members: 4 */
/* sum members: 36, holes: 1, sum holes: 4 */
/* forced alignments: 1, forced holes: 1, sum forced holes: 4 */
/* last cacheline: 40 bytes */
} __attribute__((__aligned__(8)));If you also enable CONFIG_MEMCG or enough options to make LAST_CPUPID_NOT_IN_PAGE_FLAGS true, you'll end up with another 4-byte hole at the end. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel