[patch 1/3] mmu_notifier: Core code

From: Christoph Lameter
Date: Wed Jan 30 2008 - 23:59:39 EST

Notifier functions for hardware and software that establishes external
references to pages of a Linux system. The notifier calls ensure that
external mappings are removed when the Linux VM removes memory ranges
or individual pages from a process.

These fall into two classes:

1. mmu_notifier

These are callbacks registered with an mm_struct. If pages are
removed from an address space then callbacks are performed.

Spinlocks must be held in order to walk reverse maps. The
invalidate_page() callbacks are performed with spinlocks are held.

The invalidate_range_start/end callbacks can be performed in contexts
where sleeping is allowed or in atomic contexts. A flag is passed
to indicate an atomic context.


2. mmu_rmap_notifier

Callbacks for subsystems that provide their own rmaps. These
need to walk their own rmaps for a page. The invalidate_page
callback is outside of locks so that we are not in a strictly
atomic context (but we may be in a PF_MEMALLOC context if the
notifier is called from reclaim code) and are able to sleep.

Rmap notifiers need an extra page bit and are only available
on 64 bit platforms.

Pages must be marked dirty if dirty bits are found to be set in
the external ptes.

Requirements on synchronization within the driver:

Multiple invalidate_range_begin/ends may be nested or called
concurrently. That is legit. However, no new external references
may be established as long as any invalidate_xxx is running or
any invalidate_range_begin() and has not been completed through a
corresponding call to invalidate_range_end().

Locking within the notifier needs to serialize events correspondingly.

If all invalidate_xx notifier calls take a driver lock then it is possible
to run follow_page() under the same lock. The lock can then guarantee
that no page is removed and provides an additional existence guarantee
of the page.

invalidate_range_begin() must clear all references in the range
and stop the establishment of new references.

invalidate_range_end() reenables the establishment of references.
atomic indicates that the function is called in an atomic context.
We can sleep if atomic == 0.

Signed-off-by: Christoph Lameter <clameter@xxxxxxx>
Signed-off-by: Andrea Arcangeli <andrea@xxxxxxxxxxxx>

---
include/linux/mm_types.h | 6 +
include/linux/mmu_notifier.h | 248 +++++++++++++++++++++++++++++++++++++++++++
include/linux/page-flags.h | 11 +
kernel/fork.c | 2
mm/Kconfig | 4
mm/Makefile | 1
mm/mmap.c | 3
mm/mmu_notifier.c | 118 ++++++++++++++++++++
8 files changed, 393 insertions(+)

Index: linux-2.6/include/linux/mm_types.h
===================================================================
--- linux-2.6.orig/include/linux/mm_types.h 2008-01-30 19:49:32.000000000 -0800
+++ linux-2.6/include/linux/mm_types.h 2008-01-30 19:49:34.000000000 -0800
@@ -153,6 +153,10 @@ struct vm_area_struct {
#endif
};

+struct mmu_notifier_head {
+ struct hlist_head head;
+};
+
struct mm_struct {
struct vm_area_struct * mmap; /* list of VMAs */
struct rb_root mm_rb;
@@ -219,6 +223,8 @@ struct mm_struct {
/* aio bits */
rwlock_t ioctx_list_lock;
struct kioctx *ioctx_list;
+
+ struct mmu_notifier_head mmu_notifier; /* MMU notifier list */
};

#endif /* _LINUX_MM_TYPES_H */
Index: linux-2.6/include/linux/mmu_notifier.h
===================================================================
--- /dev/null 1970-01-01 00:00:00.000000000 +0000
+++ linux-2.6/include/linux/mmu_notifier.h 2008-01-30 20:25:43.000000000 -0800
@@ -0,0 +1,248 @@
+#ifndef _LINUX_MMU_NOTIFIER_H
+#define _LINUX_MMU_NOTIFIER_H
+
+/*
+ * MMU motifier
+ *
+ * Notifier functions for hardware and software that establishes external
+ * references to pages of a Linux system. The notifier calls ensure that
+ * external mappings are removed when the Linux VM removes memory ranges
+ * or individual pages from a process.
+ *
+ * These fall into two classes
+ *
+ * 1. mmu_notifier
+ *
+ * These are callbacks registered with an mm_struct. If mappings are
+ * removed from an address space then callbacks are performed.
+ *
+ * Spinlocks must be held in order to walk reverse maps. The
+ * invalidate_page notifications are performed with spinlocks are held.
+ *
+ * The invalidate_range_start/end callbacks can be performed in contexts
+ * where sleeping is allowed or in atomic contexts. A flag is passed
+ * to indicate an atomic context.
+ *
+ *
+ * 2. mmu_rmap_notifier
+ *
+ * Callbacks for subsystems that provide their own rmaps. These
+ * need to walk their own rmaps for a page. The invalidate_page
+ * callback is outside of locks so that we are not in a strictly
+ * atomic context (but we may be in a PF_MEMALLOC context if the
+ * notifier is called from reclaim code) and are able to sleep.
+ *
+ * Rmap notifiers need an extra page bit and are only available
+ * on 64 bit platforms.
+ *
+ * Pages must be marked dirty if dirty bits found to be set in
+ * the external ptes.
+ */
+
+#include <linux/list.h>
+#include <linux/spinlock.h>
+#include <linux/rcupdate.h>
+#include <linux/mm_types.h>
+
+struct mmu_notifier_ops;
+
+struct mmu_notifier {
+ struct hlist_node hlist;
+ const struct mmu_notifier_ops *ops;
+};
+
+struct mmu_notifier_ops {
+ /*
+ * The release notifier is called when no other execution threads
+ * are left. Synchronization is not necessary.
+ */
+ void (*release)(struct mmu_notifier *mn,
+ struct mm_struct *mm);
+
+ /* Dummy needed because the mmu_notifier() macro requires it */
+ void (*invalidate_all)(struct mmu_notifier *mn, struct mm_struct *mm,
+ int dummy);
+
+ /*
+ * age_page is called from contexts where the pte_lock is held
+ */
+ int (*age_page)(struct mmu_notifier *mn,
+ struct mm_struct *mm,
+ unsigned long address);
+
+ /* invalidate_page is called from contexts where the pte_lock is held */
+ void (*invalidate_page)(struct mmu_notifier *mn,
+ struct mm_struct *mm,
+ unsigned long address);
+
+ /*
+ * invalidate_range_begin() and invalidate_range_end() must paired.
+ * Multiple invalidate_range_begin/ends may be nested or called
+ * concurrently. That is legit. However, no new external references
+ * may be established as long as any invalidate_xxx is running or
+ * any invalidate_range_begin() and has not been completed through a
+ * corresponding call to invalidate_range_end().
+ *
+ * Locking within the notifier needs to serialize events correspondingly.
+ *
+ * If all invalidate_xx notifier calls take a driver lock then it is possible
+ * to run follow_page() under the same lock. The lock can then guarantee
+ * that no page is removed. That way we can avoid increasing the refcount
+ * of the pages.
+ *
+ * invalidate_range_begin() must clear all references in the range
+ * and stop the establishment of new references.
+ *
+ * invalidate_range_end() reenables the establishment of references.
+ *
+ * atomic indicates that the function is called in an atomic context.
+ * We can sleep if atomic == 0.
+ */
+ void (*invalidate_range_begin)(struct mmu_notifier *mn,
+ struct mm_struct *mm,
+ unsigned long start, unsigned long end,
+ int atomic);
+
+ void (*invalidate_range_end)(struct mmu_notifier *mn,
+ struct mm_struct *mm, int atomic);
+};
+
+struct mmu_rmap_notifier_ops;
+
+struct mmu_rmap_notifier {
+ struct hlist_node hlist;
+ const struct mmu_rmap_notifier_ops *ops;
+};
+
+struct mmu_rmap_notifier_ops {
+ /*
+ * Called with the page lock held after ptes are modified or removed
+ * so that a subsystem with its own rmap's can remove remote ptes
+ * mapping a page.
+ */
+ void (*invalidate_page)(struct mmu_rmap_notifier *mrn,
+ struct page *page);
+};
+
+#ifdef CONFIG_MMU_NOTIFIER
+
+/*
+ * Must hold the mmap_sem for write.
+ *
+ * RCU is used to traverse the list. A quiescent period needs to pass
+ * before the notifier is guaranteed to be visible to all threads
+ */
+extern void __mmu_notifier_register(struct mmu_notifier *mn,
+ struct mm_struct *mm);
+/* Will acquire mmap_sem for write*/
+extern void mmu_notifier_register(struct mmu_notifier *mn,
+ struct mm_struct *mm);
+/*
+ * Will acquire mmap_sem for write.
+ *
+ * A quiescent period needs to pass before the mmu_notifier structure
+ * can be released. mmu_notifier_release() will wait for a quiescent period
+ * after calling the ->release callback. So it is safe to call
+ * mmu_notifier_unregister from the ->release function.
+ */
+extern void mmu_notifier_unregister(struct mmu_notifier *mn,
+ struct mm_struct *mm);
+
+
+extern void mmu_notifier_release(struct mm_struct *mm);
+extern int mmu_notifier_age_page(struct mm_struct *mm,
+ unsigned long address);
+
+static inline void mmu_notifier_head_init(struct mmu_notifier_head *mnh)
+{
+ INIT_HLIST_HEAD(&mnh->head);
+}
+
+#define mmu_notifier(function, mm, args...) \
+ do { \
+ struct mmu_notifier *__mn; \
+ struct hlist_node *__n; \
+ \
+ if (unlikely(!hlist_empty(&(mm)->mmu_notifier.head))) { \
+ rcu_read_lock(); \
+ hlist_for_each_entry_rcu(__mn, __n, \
+ &(mm)->mmu_notifier.head, \
+ hlist) \
+ if (__mn->ops->function) \
+ __mn->ops->function(__mn, \
+ mm, \
+ args); \
+ rcu_read_unlock(); \
+ } \
+ } while (0)
+
+extern void mmu_rmap_notifier_register(struct mmu_rmap_notifier *mrn);
+extern void mmu_rmap_notifier_unregister(struct mmu_rmap_notifier *mrn);
+
+/* Must hold PageLock */
+extern void mmu_rmap_export_page(struct page *page);
+
+extern struct hlist_head mmu_rmap_notifier_list;
+
+#define mmu_rmap_notifier(function, args...) \
+ do { \
+ struct mmu_rmap_notifier *__mrn; \
+ struct hlist_node *__n; \
+ \
+ rcu_read_lock(); \
+ hlist_for_each_entry_rcu(__mrn, __n, \
+ &mmu_rmap_notifier_list, hlist) \
+ if (__mrn->ops->function) \
+ __mrn->ops->function(__mrn, args); \
+ rcu_read_unlock(); \
+ } while (0);
+
+#else /* CONFIG_MMU_NOTIFIER */
+
+/*
+ * Notifiers that use the parameters that they were passed so that the
+ * compiler does not complain about unused variables but does proper
+ * parameter checks even if !CONFIG_MMU_NOTIFIER.
+ * Macros generate no code.
+ */
+#define mmu_notifier(function, mm, args...) \
+ do { \
+ if (0) { \
+ struct mmu_notifier *__mn; \
+ \
+ __mn = (struct mmu_notifier *)(0x00ff); \
+ __mn->ops->function(__mn, mm, args); \
+ }; \
+ } while (0)
+
+#define mmu_rmap_notifier(function, args...) \
+ do { \
+ if (0) { \
+ struct mmu_rmap_notifier *__mrn; \
+ \
+ __mrn = (struct mmu_rmap_notifier *)(0x00ff); \
+ __mrn->ops->function(__mrn, args); \
+ } \
+ } while (0);
+
+static inline void mmu_notifier_register(struct mmu_notifier *mn,
+ struct mm_struct *mm) {}
+static inline void mmu_notifier_unregister(struct mmu_notifier *mn,
+ struct mm_struct *mm) {}
+static inline void mmu_notifier_release(struct mm_struct *mm) {}
+static inline int mmu_notifier_age_page(struct mm_struct *mm,
+ unsigned long address)
+{
+ return 0;
+}
+
+static inline void mmu_notifier_head_init(struct mmu_notifier_head *mmh) {}
+
+static inline void mmu_rmap_notifier_register(struct mmu_rmap_notifier *mrn)
+ {}
+static inline void mmu_rmap_notifier_unregister(struct mmu_rmap_notifier *mrn)
+ {}
+
+#endif /* CONFIG_MMU_NOTIFIER */
+
+#endif /* _LINUX_MMU_NOTIFIER_H */
Index: linux-2.6/include/linux/page-flags.h
===================================================================
--- linux-2.6.orig/include/linux/page-flags.h 2008-01-30 19:49:32.000000000 -0800
+++ linux-2.6/include/linux/page-flags.h 2008-01-30 20:30:50.000000000 -0800
@@ -105,6 +105,7 @@
* 64 bit | FIELDS | ?????? FLAGS |
* 63 32 0
*/
+#define PG_external_rmap 30 /* Page has external rmap */
#define PG_uncached 31 /* Page has been mapped as uncached */
#endif

@@ -260,6 +261,16 @@ static inline void __ClearPageTail(struc
#define SetPageUncached(page) set_bit(PG_uncached, &(page)->flags)
#define ClearPageUncached(page) clear_bit(PG_uncached, &(page)->flags)

+#if defined(CONFIG_MMU_NOTIFIER) && defined(CONFIG_64BIT)
+#define PageExternalRmap(page) test_bit(PG_external_rmap, &(page)->flags)
+#define SetPageExternalRmap(page) set_bit(PG_external_rmap, &(page)->flags)
+#define ClearPageExternalRmap(page) clear_bit(PG_external_rmap, \
+ &(page)->flags)
+#else
+#define ClearPageExternalRmap(page) do {} while (0)
+#define PageExternalRmap(page) 0
+#endif
+
struct page; /* forward declaration */

extern void cancel_dirty_page(struct page *page, unsigned int account_size);
Index: linux-2.6/mm/Kconfig
===================================================================
--- linux-2.6.orig/mm/Kconfig 2008-01-30 19:49:32.000000000 -0800
+++ linux-2.6/mm/Kconfig 2008-01-30 19:49:34.000000000 -0800
@@ -193,3 +193,7 @@ config NR_QUICK
config VIRT_TO_BUS
def_bool y
depends on !ARCH_NO_VIRT_TO_BUS
+
+config MMU_NOTIFIER
+ def_bool y
+ bool "MMU notifier, for paging KVM/RDMA"
Index: linux-2.6/mm/Makefile
===================================================================
--- linux-2.6.orig/mm/Makefile 2008-01-30 19:49:32.000000000 -0800
+++ linux-2.6/mm/Makefile 2008-01-30 19:49:34.000000000 -0800
@@ -30,4 +30,5 @@ obj-$(CONFIG_FS_XIP) += filemap_xip.o
obj-$(CONFIG_MIGRATION) += migrate.o
obj-$(CONFIG_SMP) += allocpercpu.o
obj-$(CONFIG_QUICKLIST) += quicklist.o
+obj-$(CONFIG_MMU_NOTIFIER) += mmu_notifier.o

Index: linux-2.6/mm/mmu_notifier.c
===================================================================
--- /dev/null 1970-01-01 00:00:00.000000000 +0000
+++ linux-2.6/mm/mmu_notifier.c 2008-01-30 20:31:12.000000000 -0800
@@ -0,0 +1,118 @@
+/*
+ * linux/mm/mmu_notifier.c
+ *
+ * Copyright (C) 2008 Qumranet, Inc.
+ * Copyright (C) 2008 SGI
+ * Christoph Lameter <clameter@xxxxxxx>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2. See
+ * the COPYING file in the top-level directory.
+ */
+
+#include <linux/module.h>
+#include <linux/mm.h>
+#include <linux/mmu_notifier.h>
+
+/*
+ * No synchronization. This function can only be called when only a single
+ * process remains that performs teardown.
+ */
+void mmu_notifier_release(struct mm_struct *mm)
+{
+ struct mmu_notifier *mn;
+ struct hlist_node *n, *t;
+
+ if (unlikely(!hlist_empty(&mm->mmu_notifier.head))) {
+ hlist_for_each_entry_safe(mn, n, t,
+ &mm->mmu_notifier.head, hlist) {
+ hlist_del_init(&mn->hlist);
+ if (mn->ops->release)
+ mn->ops->release(mn, mm);
+ }
+ }
+}
+
+/*
+ * If no young bitflag is supported by the hardware, ->age_page can
+ * unmap the address and return 1 or 0 depending if the mapping previously
+ * existed or not.
+ */
+int mmu_notifier_age_page(struct mm_struct *mm, unsigned long address)
+{
+ struct mmu_notifier *mn;
+ struct hlist_node *n;
+ int young = 0;
+
+ if (unlikely(!hlist_empty(&mm->mmu_notifier.head))) {
+ rcu_read_lock();
+ hlist_for_each_entry_rcu(mn, n,
+ &mm->mmu_notifier.head, hlist) {
+ if (mn->ops->age_page)
+ young |= mn->ops->age_page(mn, mm, address);
+ }
+ rcu_read_unlock();
+ }
+
+ return young;
+}
+
+/*
+ * Note that all notifiers use RCU. The updates are only guaranteed to be
+ * visible to other processes after a RCU quiescent period!
+ */
+void __mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
+{
+ hlist_add_head_rcu(&mn->hlist, &mm->mmu_notifier.head);
+}
+EXPORT_SYMBOL_GPL(__mmu_notifier_register);
+
+void mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
+{
+ down_write(&mm->mmap_sem);
+ __mmu_notifier_register(mn, mm);
+ up_write(&mm->mmap_sem);
+}
+EXPORT_SYMBOL_GPL(mmu_notifier_register);
+
+void mmu_notifier_unregister(struct mmu_notifier *mn, struct mm_struct *mm)
+{
+ down_write(&mm->mmap_sem);
+ hlist_del_rcu(&mn->hlist);
+ up_write(&mm->mmap_sem);
+}
+EXPORT_SYMBOL_GPL(mmu_notifier_unregister);
+
+#ifdef CONFIG_64BIT
+static DEFINE_SPINLOCK(mmu_notifier_list_lock);
+HLIST_HEAD(mmu_rmap_notifier_list);
+
+void mmu_rmap_notifier_register(struct mmu_rmap_notifier *mrn)
+{
+ spin_lock(&mmu_notifier_list_lock);
+ hlist_add_head_rcu(&mrn->hlist, &mmu_rmap_notifier_list);
+ spin_unlock(&mmu_notifier_list_lock);
+}
+EXPORT_SYMBOL(mmu_rmap_notifier_register);
+
+void mmu_rmap_notifier_unregister(struct mmu_rmap_notifier *mrn)
+{
+ spin_lock(&mmu_notifier_list_lock);
+ hlist_del_rcu(&mrn->hlist);
+ spin_unlock(&mmu_notifier_list_lock);
+}
+EXPORT_SYMBOL(mmu_rmap_notifier_unregister);
+
+/*
+ * Export a page.
+ *
+ * Pagelock must be held.
+ * Must be called before a page is put on an external rmap.
+ */
+void mmu_rmap_export_page(struct page *page)
+{
+ BUG_ON(!PageLocked(page));
+ SetPageExternalRmap(page);
+}
+EXPORT_SYMBOL(mmu_rmap_export_page);
+
+#endif
Index: linux-2.6/kernel/fork.c
===================================================================
--- linux-2.6.orig/kernel/fork.c 2008-01-30 19:49:32.000000000 -0800
+++ linux-2.6/kernel/fork.c 2008-01-30 19:49:34.000000000 -0800
@@ -52,6 +52,7 @@
#include <linux/tty.h>
#include <linux/proc_fs.h>
#include <linux/blkdev.h>
+#include <linux/mmu_notifier.h>

#include <asm/pgtable.h>
#include <asm/pgalloc.h>
@@ -360,6 +361,7 @@ static struct mm_struct * mm_init(struct

if (likely(!mm_alloc_pgd(mm))) {
mm->def_flags = 0;
+ mmu_notifier_head_init(&mm->mmu_notifier);
return mm;
}
free_mm(mm);
Index: linux-2.6/mm/mmap.c
===================================================================
--- linux-2.6.orig/mm/mmap.c 2008-01-30 19:49:32.000000000 -0800
+++ linux-2.6/mm/mmap.c 2008-01-30 20:29:31.000000000 -0800
@@ -26,6 +26,7 @@
#include <linux/mount.h>
#include <linux/mempolicy.h>
#include <linux/rmap.h>
+#include <linux/mmu_notifier.h>

#include <asm/uaccess.h>
#include <asm/cacheflush.h>
@@ -2033,6 +2034,7 @@ void exit_mmap(struct mm_struct *mm)
unsigned long end;

/* mm's last user has gone, and its about to be pulled down */
+ mmu_notifier(invalidate_all, mm, 0);
arch_exit_mmap(mm);

lru_add_drain();
@@ -2044,6 +2046,7 @@ void exit_mmap(struct mm_struct *mm)
vm_unacct_memory(nr_accounted);
free_pgtables(&tlb, vma, FIRST_USER_ADDRESS, 0);
tlb_finish_mmu(tlb, 0, end);
+ mmu_notifier_release(mm);

/*
* Walk the list again, actually closing and freeing it,

--
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