From: Matthew Wilcox <willy@infradead.org>
To: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Cc: Jesper Dangaard Brouer <brouer@redhat.com>,
kernel test robot <lkp@intel.com>, Linux-MM <linux-mm@kvack.org>,
kbuild-all@lists.01.org, clang-built-linux@googlegroups.com,
open list <linux-kernel@vger.kernel.org>,
linux-fsdevel@vger.kernel.org,
Michael Ellerman <mpe@ellerman.id.au>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>,
linuxppc-dev@lists.ozlabs.org,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
"David S. Miller" <davem@davemloft.net>,
Ivan Khoronzhuk <ivan.khoronzhuk@linaro.org>,
Matteo Croce <mcroce@linux.microsoft.com>,
"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
Grygorii Strashko <grygorii.strashko@ti.com>
Subject: Re: Bogus struct page layout on 32-bit
Date: Sat, 10 Apr 2021 15:06:52 +0100 [thread overview]
Message-ID: <20210410140652.GY2531743@casper.infradead.org> (raw)
In-Reply-To: <CAC_iWjLXZ6-hhvmvee6r4R_N64u-hrnLqE_CSS1nQk+YaMQQnA@mail.gmail.com>
How about moving the flags into the union? A bit messy, but we don't
have to play games with __packed__.
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 1210a8e41fad..f374d2f06255 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -68,16 +68,22 @@ struct mem_cgroup;
#endif
struct page {
- unsigned long flags; /* Atomic flags, some possibly
- * updated asynchronously */
/*
- * Five words (20/40 bytes) are available in this union.
- * WARNING: bit 0 of the first word is used for PageTail(). That
- * means the other users of this union MUST NOT use the bit to
+ * This union is six words (24 / 48 bytes) in size.
+ * The first word is reserved for atomic flags, often updated
+ * asynchronously. Use the PageFoo() macros to access it. Some
+ * of the flags can be reused for your own purposes, but the
+ * word as a whole often contains other information and overwriting
+ * it will cause functions like page_zone() and page_node() to stop
+ * working correctly.
+ *
+ * Bit 0 of the second word is used for PageTail(). That
+ * means the other users of this union MUST leave the bit zero to
* avoid collision and false-positive PageTail().
*/
union {
struct { /* Page cache and anonymous pages */
+ unsigned long flags;
/**
* @lru: Pageout list, eg. active_list protected by
* lruvec->lru_lock. Sometimes used as a generic list
@@ -96,6 +102,8 @@ struct page {
unsigned long private;
};
struct { /* page_pool used by netstack */
+ unsigned long _pp_flags;
+ unsigned long _pp_pad;
/**
* @dma_addr: might require a 64-bit value even on
* 32-bit architectures.
@@ -103,6 +111,7 @@ struct page {
dma_addr_t dma_addr;
};
struct { /* slab, slob and slub */
+ unsigned long _slab_flags;
union {
struct list_head slab_list;
struct { /* Partial pages */
@@ -130,6 +139,7 @@ struct page {
};
};
struct { /* Tail pages of compound page */
+ unsigned long _tail1_flags;
unsigned long compound_head; /* Bit zero is set */
/* First tail page only */
@@ -139,12 +149,14 @@ struct page {
unsigned int compound_nr; /* 1 << compound_order */
};
struct { /* Second tail page of compound page */
+ unsigned long _tail2_flags;
unsigned long _compound_pad_1; /* compound_head */
atomic_t hpage_pinned_refcount;
/* For both global and memcg */
struct list_head deferred_list;
};
struct { /* Page table pages */
+ unsigned long _pt_flags;
unsigned long _pt_pad_1; /* compound_head */
pgtable_t pmd_huge_pte; /* protected by page->ptl */
unsigned long _pt_pad_2; /* mapping */
@@ -159,6 +171,7 @@ struct page {
#endif
};
struct { /* ZONE_DEVICE pages */
+ unsigned long _zd_flags;
/** @pgmap: Points to the hosting device page map. */
struct dev_pagemap *pgmap;
void *zone_device_data;
@@ -174,8 +187,11 @@ struct page {
*/
};
- /** @rcu_head: You can use this to free a page by RCU. */
- struct rcu_head rcu_head;
+ struct {
+ unsigned long _rcu_flags;
+ /** @rcu_head: You can use this to free a page by RCU. */
+ struct rcu_head rcu_head;
+ };
};
union { /* This union is 4 bytes in size. */
next prev parent reply other threads:[~2021-04-10 14:08 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-09 18:50 [PATCH v7 00/28] Memory Folios Matthew Wilcox (Oracle)
2021-04-09 18:50 ` [PATCH v7 01/28] mm: Optimise nth_page for contiguous memmap Matthew Wilcox (Oracle)
2021-04-12 6:08 ` Christoph Hellwig
2021-04-09 18:50 ` [PATCH v7 02/28] mm: Introduce struct folio Matthew Wilcox (Oracle)
2021-04-09 22:45 ` kernel test robot
2021-04-10 2:43 ` Bogus struct page layout on 32-bit Matthew Wilcox
2021-04-10 6:21 ` Jesper Dangaard Brouer
2021-04-10 8:52 ` Ilias Apalodimas
2021-04-10 14:06 ` Matthew Wilcox [this message]
2021-04-10 15:54 ` Russell King - ARM Linux admin
2021-04-16 9:26 ` Grygorii Strashko
2021-04-16 14:10 ` Arnd Bergmann
2021-04-17 13:08 ` David Laight
2021-04-10 14:17 ` David Laight
2021-04-10 19:10 ` Arnd Bergmann
2021-04-11 22:35 ` Matthew Wilcox
2021-04-10 2:51 ` [PATCH v7 02/28] mm: Introduce struct folio kernel test robot
2021-04-16 15:55 ` Matthew Wilcox
2021-04-19 9:06 ` Kirill A. Shutemov
2021-04-09 18:50 ` [PATCH v7 03/28] mm: Add folio_pgdat and folio_zone Matthew Wilcox (Oracle)
2021-04-09 18:50 ` [PATCH v7 04/28] mm/vmstat: Add functions to account folio statistics Matthew Wilcox (Oracle)
2021-04-09 18:50 ` [PATCH v7 05/28] mm/debug: Add VM_BUG_ON_FOLIO and VM_WARN_ON_ONCE_FOLIO Matthew Wilcox (Oracle)
2021-04-09 18:50 ` [PATCH v7 06/28] mm: Add folio reference count functions Matthew Wilcox (Oracle)
2021-04-09 18:50 ` [PATCH v7 07/28] mm: Add put_folio Matthew Wilcox (Oracle)
2021-04-09 18:50 ` [PATCH v7 08/28] mm: Add get_folio Matthew Wilcox (Oracle)
2021-04-09 18:50 ` [PATCH v7 09/28] mm: Create FolioFlags Matthew Wilcox (Oracle)
2021-04-19 13:25 ` Peter Zijlstra
2021-04-19 13:55 ` Matthew Wilcox
2021-04-09 18:50 ` [PATCH v7 10/28] mm: Handle per-folio private data Matthew Wilcox (Oracle)
2021-04-09 18:50 ` [PATCH v7 11/28] mm/filemap: Add folio_index, folio_file_page and folio_contains Matthew Wilcox (Oracle)
2021-04-09 18:50 ` [PATCH v7 12/28] mm/filemap: Add folio_next_index Matthew Wilcox (Oracle)
2021-04-09 18:50 ` [PATCH v7 13/28] mm/filemap: Add folio_offset and folio_file_offset Matthew Wilcox (Oracle)
2021-04-09 18:50 ` [PATCH v7 14/28] mm/util: Add folio_mapping and folio_file_mapping Matthew Wilcox (Oracle)
2021-04-09 18:50 ` [PATCH v7 15/28] mm: Add folio_mapcount Matthew Wilcox (Oracle)
2021-04-09 18:50 ` [PATCH v7 16/28] mm/memcg: Add folio wrappers for various functions Matthew Wilcox (Oracle)
2021-04-09 18:50 ` [PATCH v7 17/28] mm/filemap: Add unlock_folio Matthew Wilcox (Oracle)
2021-04-09 18:50 ` [PATCH v7 18/28] mm/filemap: Add lock_folio Matthew Wilcox (Oracle)
2021-04-09 18:50 ` [PATCH v7 19/28] mm/filemap: Add lock_folio_killable Matthew Wilcox (Oracle)
2021-04-09 18:50 ` [PATCH v7 20/28] mm/filemap: Add __lock_folio_async Matthew Wilcox (Oracle)
2021-04-09 18:50 ` [PATCH v7 21/28] mm/filemap: Add __lock_folio_or_retry Matthew Wilcox (Oracle)
2021-04-09 18:50 ` [PATCH v7 22/28] mm/filemap: Add wait_on_folio_locked Matthew Wilcox (Oracle)
2021-04-09 18:51 ` [PATCH v7 23/28] mm/filemap: Add end_folio_writeback Matthew Wilcox (Oracle)
2021-04-09 18:51 ` [PATCH v7 24/28] mm/writeback: Add wait_on_folio_writeback Matthew Wilcox (Oracle)
2021-04-09 18:51 ` [PATCH v7 25/28] mm/writeback: Add wait_for_stable_folio Matthew Wilcox (Oracle)
2021-04-09 18:51 ` [PATCH v7 26/28] mm/filemap: Convert wait_on_page_bit to wait_on_folio_bit Matthew Wilcox (Oracle)
2021-04-09 18:51 ` [PATCH v7 27/28] mm/filemap: Convert wake_up_page_bit to wake_up_folio_bit Matthew Wilcox (Oracle)
2021-04-09 18:51 ` [PATCH v7 28/28] mm/filemap: Convert page wait queues to be folios Matthew Wilcox (Oracle)
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