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![Izik Eidus](/assets/img/avatar_default.png)
KSM is a linux driver that allows dynamicly sharing identical memory pages between one or more processes. Unlike tradtional page sharing that is made at the allocation of the memory, ksm do it dynamicly after the memory was created. Memory is periodically scanned; identical pages are identified and merged. The sharing is made in a transparent way to the processes that use it. Ksm is highly important for hypervisors (kvm), where in production enviorments there might be many copys of the same data data among the host memory. This kind of data can be: similar kernels, librarys, cache, and so on. Even that ksm was wrote for kvm, any userspace application that want to use it to share its data can try it. Ksm may be useful for any application that might have similar (page aligment) data strctures among the memory, ksm will find this data merge it to one copy, and even if it will be changed and thereforew copy on writed, ksm will merge it again as soon as it will be identical again. Another reason to consider using ksm is the fact that it might simplify alot the userspace code of application that want to use shared private data, instead that the application will mange shared area, ksm will do this for the application, and even write to this data will be allowed without any synchinization acts from the application. Ksm was designed to be a loadable module that doesn't change the VM code of linux. This patch: The set_pte_at_notify() macro allows setting a pte in the shadow page table directly, instead of flushing the shadow page table entry and then getting vmexit to set it. It uses a new change_pte() callback to do so. set_pte_at_notify() is an optimization for kvm, and other users of mmu_notifiers, for COW pages. It is useful for kvm when ksm is used, because it allows kvm not to have to receive vmexit and only then map the ksm page into the shadow page table, but instead map it directly at the same time as Linux maps the page into the host page table. Users of mmu_notifiers who don't implement new mmu_notifier_change_pte() callback will just receive the mmu_notifier_invalidate_page() callback. Signed-off-by: Izik Eidus <ieidus@redhat.com> Signed-off-by: Chris Wright <chrisw@redhat.com> Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Rik van Riel <riel@redhat.com> Cc: Wu Fengguang <fengguang.wu@intel.com> Cc: Balbir Singh <balbir@in.ibm.com> Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: Lee Schermerhorn <lee.schermerhorn@hp.com> Cc: Avi Kivity <avi@redhat.com> Cc: Nick Piggin <nickpiggin@yahoo.com.au> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
313 lines
10 KiB
C
313 lines
10 KiB
C
#ifndef _LINUX_MMU_NOTIFIER_H
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#define _LINUX_MMU_NOTIFIER_H
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#include <linux/list.h>
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#include <linux/spinlock.h>
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#include <linux/mm_types.h>
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struct mmu_notifier;
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struct mmu_notifier_ops;
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#ifdef CONFIG_MMU_NOTIFIER
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/*
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* The mmu notifier_mm structure is allocated and installed in
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* mm->mmu_notifier_mm inside the mm_take_all_locks() protected
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* critical section and it's released only when mm_count reaches zero
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* in mmdrop().
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*/
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struct mmu_notifier_mm {
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/* all mmu notifiers registerd in this mm are queued in this list */
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struct hlist_head list;
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/* to serialize the list modifications and hlist_unhashed */
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spinlock_t lock;
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};
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struct mmu_notifier_ops {
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/*
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* Called either by mmu_notifier_unregister or when the mm is
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* being destroyed by exit_mmap, always before all pages are
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* freed. This can run concurrently with other mmu notifier
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* methods (the ones invoked outside the mm context) and it
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* should tear down all secondary mmu mappings and freeze the
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* secondary mmu. If this method isn't implemented you've to
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* be sure that nothing could possibly write to the pages
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* through the secondary mmu by the time the last thread with
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* tsk->mm == mm exits.
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*
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* As side note: the pages freed after ->release returns could
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* be immediately reallocated by the gart at an alias physical
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* address with a different cache model, so if ->release isn't
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* implemented because all _software_ driven memory accesses
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* through the secondary mmu are terminated by the time the
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* last thread of this mm quits, you've also to be sure that
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* speculative _hardware_ operations can't allocate dirty
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* cachelines in the cpu that could not be snooped and made
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* coherent with the other read and write operations happening
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* through the gart alias address, so leading to memory
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* corruption.
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*/
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void (*release)(struct mmu_notifier *mn,
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struct mm_struct *mm);
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/*
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* clear_flush_young is called after the VM is
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* test-and-clearing the young/accessed bitflag in the
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* pte. This way the VM will provide proper aging to the
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* accesses to the page through the secondary MMUs and not
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* only to the ones through the Linux pte.
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*/
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int (*clear_flush_young)(struct mmu_notifier *mn,
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struct mm_struct *mm,
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unsigned long address);
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/*
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* change_pte is called in cases that pte mapping to page is changed:
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* for example, when ksm remaps pte to point to a new shared page.
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*/
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void (*change_pte)(struct mmu_notifier *mn,
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struct mm_struct *mm,
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unsigned long address,
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pte_t pte);
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/*
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* Before this is invoked any secondary MMU is still ok to
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* read/write to the page previously pointed to by the Linux
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* pte because the page hasn't been freed yet and it won't be
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* freed until this returns. If required set_page_dirty has to
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* be called internally to this method.
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*/
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void (*invalidate_page)(struct mmu_notifier *mn,
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struct mm_struct *mm,
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unsigned long address);
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/*
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* invalidate_range_start() and invalidate_range_end() must be
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* paired and are called only when the mmap_sem and/or the
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* locks protecting the reverse maps are held. The subsystem
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* must guarantee that no additional references are taken to
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* the pages in the range established between the call to
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* invalidate_range_start() and the matching call to
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* invalidate_range_end().
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*
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* Invalidation of multiple concurrent ranges may be
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* optionally permitted by the driver. Either way the
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* establishment of sptes is forbidden in the range passed to
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* invalidate_range_begin/end for the whole duration of the
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* invalidate_range_begin/end critical section.
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*
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* invalidate_range_start() is called when all pages in the
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* range are still mapped and have at least a refcount of one.
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*
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* invalidate_range_end() is called when all pages in the
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* range have been unmapped and the pages have been freed by
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* the VM.
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*
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* The VM will remove the page table entries and potentially
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* the page between invalidate_range_start() and
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* invalidate_range_end(). If the page must not be freed
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* because of pending I/O or other circumstances then the
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* invalidate_range_start() callback (or the initial mapping
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* by the driver) must make sure that the refcount is kept
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* elevated.
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*
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* If the driver increases the refcount when the pages are
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* initially mapped into an address space then either
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* invalidate_range_start() or invalidate_range_end() may
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* decrease the refcount. If the refcount is decreased on
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* invalidate_range_start() then the VM can free pages as page
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* table entries are removed. If the refcount is only
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* droppped on invalidate_range_end() then the driver itself
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* will drop the last refcount but it must take care to flush
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* any secondary tlb before doing the final free on the
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* page. Pages will no longer be referenced by the linux
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* address space but may still be referenced by sptes until
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* the last refcount is dropped.
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*/
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void (*invalidate_range_start)(struct mmu_notifier *mn,
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struct mm_struct *mm,
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unsigned long start, unsigned long end);
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void (*invalidate_range_end)(struct mmu_notifier *mn,
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struct mm_struct *mm,
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unsigned long start, unsigned long end);
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};
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/*
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* The notifier chains are protected by mmap_sem and/or the reverse map
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* semaphores. Notifier chains are only changed when all reverse maps and
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* the mmap_sem locks are taken.
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*
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* Therefore notifier chains can only be traversed when either
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*
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* 1. mmap_sem is held.
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* 2. One of the reverse map locks is held (i_mmap_lock or anon_vma->lock).
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* 3. No other concurrent thread can access the list (release)
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*/
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struct mmu_notifier {
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struct hlist_node hlist;
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const struct mmu_notifier_ops *ops;
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};
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static inline int mm_has_notifiers(struct mm_struct *mm)
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{
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return unlikely(mm->mmu_notifier_mm);
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}
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extern int mmu_notifier_register(struct mmu_notifier *mn,
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struct mm_struct *mm);
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extern int __mmu_notifier_register(struct mmu_notifier *mn,
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struct mm_struct *mm);
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extern void mmu_notifier_unregister(struct mmu_notifier *mn,
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struct mm_struct *mm);
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extern void __mmu_notifier_mm_destroy(struct mm_struct *mm);
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extern void __mmu_notifier_release(struct mm_struct *mm);
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extern int __mmu_notifier_clear_flush_young(struct mm_struct *mm,
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unsigned long address);
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extern void __mmu_notifier_change_pte(struct mm_struct *mm,
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unsigned long address, pte_t pte);
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extern void __mmu_notifier_invalidate_page(struct mm_struct *mm,
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unsigned long address);
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extern void __mmu_notifier_invalidate_range_start(struct mm_struct *mm,
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unsigned long start, unsigned long end);
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extern void __mmu_notifier_invalidate_range_end(struct mm_struct *mm,
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unsigned long start, unsigned long end);
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static inline void mmu_notifier_release(struct mm_struct *mm)
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{
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if (mm_has_notifiers(mm))
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__mmu_notifier_release(mm);
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}
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static inline int mmu_notifier_clear_flush_young(struct mm_struct *mm,
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unsigned long address)
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{
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if (mm_has_notifiers(mm))
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return __mmu_notifier_clear_flush_young(mm, address);
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return 0;
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}
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static inline void mmu_notifier_change_pte(struct mm_struct *mm,
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unsigned long address, pte_t pte)
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{
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if (mm_has_notifiers(mm))
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__mmu_notifier_change_pte(mm, address, pte);
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}
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static inline void mmu_notifier_invalidate_page(struct mm_struct *mm,
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unsigned long address)
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{
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if (mm_has_notifiers(mm))
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__mmu_notifier_invalidate_page(mm, address);
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}
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static inline void mmu_notifier_invalidate_range_start(struct mm_struct *mm,
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unsigned long start, unsigned long end)
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{
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if (mm_has_notifiers(mm))
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__mmu_notifier_invalidate_range_start(mm, start, end);
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}
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static inline void mmu_notifier_invalidate_range_end(struct mm_struct *mm,
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unsigned long start, unsigned long end)
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{
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if (mm_has_notifiers(mm))
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__mmu_notifier_invalidate_range_end(mm, start, end);
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}
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static inline void mmu_notifier_mm_init(struct mm_struct *mm)
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{
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mm->mmu_notifier_mm = NULL;
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}
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static inline void mmu_notifier_mm_destroy(struct mm_struct *mm)
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{
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if (mm_has_notifiers(mm))
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__mmu_notifier_mm_destroy(mm);
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}
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/*
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* These two macros will sometime replace ptep_clear_flush.
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* ptep_clear_flush is impleemnted as macro itself, so this also is
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* implemented as a macro until ptep_clear_flush will converted to an
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* inline function, to diminish the risk of compilation failure. The
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* invalidate_page method over time can be moved outside the PT lock
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* and these two macros can be later removed.
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*/
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#define ptep_clear_flush_notify(__vma, __address, __ptep) \
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({ \
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pte_t __pte; \
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struct vm_area_struct *___vma = __vma; \
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unsigned long ___address = __address; \
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__pte = ptep_clear_flush(___vma, ___address, __ptep); \
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mmu_notifier_invalidate_page(___vma->vm_mm, ___address); \
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__pte; \
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})
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#define ptep_clear_flush_young_notify(__vma, __address, __ptep) \
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({ \
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int __young; \
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struct vm_area_struct *___vma = __vma; \
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unsigned long ___address = __address; \
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__young = ptep_clear_flush_young(___vma, ___address, __ptep); \
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__young |= mmu_notifier_clear_flush_young(___vma->vm_mm, \
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___address); \
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__young; \
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})
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#define set_pte_at_notify(__mm, __address, __ptep, __pte) \
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({ \
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struct mm_struct *___mm = __mm; \
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unsigned long ___address = __address; \
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pte_t ___pte = __pte; \
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\
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set_pte_at(___mm, ___address, __ptep, ___pte); \
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mmu_notifier_change_pte(___mm, ___address, ___pte); \
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})
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#else /* CONFIG_MMU_NOTIFIER */
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static inline void mmu_notifier_release(struct mm_struct *mm)
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{
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}
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static inline int mmu_notifier_clear_flush_young(struct mm_struct *mm,
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unsigned long address)
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{
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return 0;
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}
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static inline void mmu_notifier_change_pte(struct mm_struct *mm,
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unsigned long address, pte_t pte)
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{
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}
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static inline void mmu_notifier_invalidate_page(struct mm_struct *mm,
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unsigned long address)
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{
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}
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static inline void mmu_notifier_invalidate_range_start(struct mm_struct *mm,
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unsigned long start, unsigned long end)
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{
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}
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static inline void mmu_notifier_invalidate_range_end(struct mm_struct *mm,
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unsigned long start, unsigned long end)
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{
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}
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static inline void mmu_notifier_mm_init(struct mm_struct *mm)
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{
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}
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static inline void mmu_notifier_mm_destroy(struct mm_struct *mm)
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{
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}
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#define ptep_clear_flush_young_notify ptep_clear_flush_young
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#define ptep_clear_flush_notify ptep_clear_flush
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#define set_pte_at_notify set_pte_at
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#endif /* CONFIG_MMU_NOTIFIER */
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#endif /* _LINUX_MMU_NOTIFIER_H */
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