mmu_notifier.h

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#ifndef _LINUX_MMU_NOTIFIER_H
#define _LINUX_MMU_NOTIFIER_H

#include <linux/list.h>
#include <linux/spinlock.h>
#include <linux/mm_types.h>
#include <linux/srcu.h>

struct mmu_notifier;
struct mmu_notifier_ops;

#ifdef CONFIG_MMU_NOTIFIER

/*
 * The mmu notifier_mm structure is allocated and installed in
 * mm->mmu_notifier_mm inside the mm_take_all_locks() protected
 * critical section and it's released only when mm_count reaches zero
 * in mmdrop().
 */
struct mmu_notifier_mm {
    /* all mmu notifiers registerd in this mm are queued in this list */
    struct hlist_head list;
    /* to serialize the list modifications and hlist_unhashed */
    spinlock_t lock;
};

struct mmu_notifier_ops {
    /*
     * Called either by mmu_notifier_unregister or when the mm is
     * being destroyed by exit_mmap, always before all pages are
     * freed. This can run concurrently with other mmu notifier
     * methods (the ones invoked outside the mm context) and it
     * should tear down all secondary mmu mappings and freeze the
     * secondary mmu. If this method isn't implemented you've to
     * be sure that nothing could possibly write to the pages
     * through the secondary mmu by the time the last thread with
     * tsk->mm == mm exits.
     *
     * As side note: the pages freed after ->release returns could
     * be immediately reallocated by the gart at an alias physical
     * address with a different cache model, so if ->release isn't
     * implemented because all _software_ driven memory accesses
     * through the secondary mmu are terminated by the time the
     * last thread of this mm quits, you've also to be sure that
     * speculative _hardware_ operations can't allocate dirty
     * cachelines in the cpu that could not be snooped and made
     * coherent with the other read and write operations happening
     * through the gart alias address, so leading to memory
     * corruption.
     */
    void (*release)(struct mmu_notifier *mn,
            struct mm_struct *mm);

    /*
     * clear_flush_young is called after the VM is
     * test-and-clearing the young/accessed bitflag in the
     * pte. This way the VM will provide proper aging to the
     * accesses to the page through the secondary MMUs and not
     * only to the ones through the Linux pte.
     */
    int (*clear_flush_young)(struct mmu_notifier *mn,
                 struct mm_struct *mm,
                 unsigned long address);

    /*
     * test_young is called to check the young/accessed bitflag in
     * the secondary pte. This is used to know if the page is
     * frequently used without actually clearing the flag or tearing
     * down the secondary mapping on the page.
     */
    int (*test_young)(struct mmu_notifier *mn,
              struct mm_struct *mm,
              unsigned long address);

    /*
     * change_pte is called in cases that pte mapping to page is changed:
     * for example, when ksm remaps pte to point to a new shared page.
     */
    void (*change_pte)(struct mmu_notifier *mn,
               struct mm_struct *mm,
               unsigned long address,
               pte_t pte);

    /*
     * Before this is invoked any secondary MMU is still ok to
     * read/write to the page previously pointed to by the Linux
     * pte because the page hasn't been freed yet and it won't be
     * freed until this returns. If required set_page_dirty has to
     * be called internally to this method.
     */
    void (*invalidate_page)(struct mmu_notifier *mn,
                struct mm_struct *mm,
                unsigned long address);

    /*
     * invalidate_range_start() and invalidate_range_end() must be
     * paired and are called only when the mmap_sem and/or the
     * locks protecting the reverse maps are held. The subsystem
     * must guarantee that no additional references are taken to
     * the pages in the range established between the call to
     * invalidate_range_start() and the matching call to
     * invalidate_range_end().
     *
     * Invalidation of multiple concurrent ranges may be
     * optionally permitted by the driver. Either way the
     * establishment of sptes is forbidden in the range passed to
     * invalidate_range_begin/end for the whole duration of the
     * invalidate_range_begin/end critical section.
     *
     * invalidate_range_start() is called when all pages in the
     * range are still mapped and have at least a refcount of one.
     *
     * invalidate_range_end() is called when all pages in the
     * range have been unmapped and the pages have been freed by
     * the VM.
     *
     * The VM will remove the page table entries and potentially
     * the page between invalidate_range_start() and
     * invalidate_range_end(). If the page must not be freed
     * because of pending I/O or other circumstances then the
     * invalidate_range_start() callback (or the initial mapping
     * by the driver) must make sure that the refcount is kept
     * elevated.
     *
     * If the driver increases the refcount when the pages are
     * initially mapped into an address space then either
     * invalidate_range_start() or invalidate_range_end() may
     * decrease the refcount. If the refcount is decreased on
     * invalidate_range_start() then the VM can free pages as page
     * table entries are removed.  If the refcount is only
     * droppped on invalidate_range_end() then the driver itself
     * will drop the last refcount but it must take care to flush
     * any secondary tlb before doing the final free on the
     * page. Pages will no longer be referenced by the linux
     * address space but may still be referenced by sptes until
     * the last refcount is dropped.
     */
    void (*invalidate_range_start)(struct mmu_notifier *mn,
                       struct mm_struct *mm,
                       unsigned long start, unsigned long end);
    void (*invalidate_range_end)(struct mmu_notifier *mn,
                     struct mm_struct *mm,
                     unsigned long start, unsigned long end);
};

/*
 * The notifier chains are protected by mmap_sem and/or the reverse map
 * semaphores. Notifier chains are only changed when all reverse maps and
 * the mmap_sem locks are taken.
 *
 * Therefore notifier chains can only be traversed when either
 *
 * 1. mmap_sem is held.
 * 2. One of the reverse map locks is held (i_mmap_mutex or anon_vma->mutex).
 * 3. No other concurrent thread can access the list (release)
 */
struct mmu_notifier {
    struct hlist_node hlist;
    const struct mmu_notifier_ops *ops;
};

static inline int mm_has_notifiers(struct mm_struct *mm)
{
    return unlikely(mm->mmu_notifier_mm);
}

extern int mmu_notifier_register(struct mmu_notifier *mn,
                 struct mm_struct *mm);
extern int __mmu_notifier_register(struct mmu_notifier *mn,
                   struct mm_struct *mm);
extern void mmu_notifier_unregister(struct mmu_notifier *mn,
                    struct mm_struct *mm);
extern void __mmu_notifier_mm_destroy(struct mm_struct *mm);
extern void __mmu_notifier_release(struct mm_struct *mm);
extern int __mmu_notifier_clear_flush_young(struct mm_struct *mm,
                      unsigned long address);
extern int __mmu_notifier_test_young(struct mm_struct *mm,
                     unsigned long address);
extern void __mmu_notifier_change_pte(struct mm_struct *mm,
                      unsigned long address, pte_t pte);
extern void __mmu_notifier_invalidate_page(struct mm_struct *mm,
                      unsigned long address);
extern void __mmu_notifier_invalidate_range_start(struct mm_struct *mm,
                  unsigned long start, unsigned long end);
extern void __mmu_notifier_invalidate_range_end(struct mm_struct *mm,
                  unsigned long start, unsigned long end);

static inline void mmu_notifier_release(struct mm_struct *mm)
{
    if (mm_has_notifiers(mm))
        __mmu_notifier_release(mm);
}

static inline int mmu_notifier_clear_flush_young(struct mm_struct *mm,
                      unsigned long address)
{
    if (mm_has_notifiers(mm))
        return __mmu_notifier_clear_flush_young(mm, address);
    return 0;
}

static inline int mmu_notifier_test_young(struct mm_struct *mm,
                      unsigned long address)
{
    if (mm_has_notifiers(mm))
        return __mmu_notifier_test_young(mm, address);
    return 0;
}

static inline void mmu_notifier_change_pte(struct mm_struct *mm,
                       unsigned long address, pte_t pte)
{
    if (mm_has_notifiers(mm))
        __mmu_notifier_change_pte(mm, address, pte);
}

static inline void mmu_notifier_invalidate_page(struct mm_struct *mm,
                      unsigned long address)
{
    if (mm_has_notifiers(mm))
        __mmu_notifier_invalidate_page(mm, address);
}

static inline void mmu_notifier_invalidate_range_start(struct mm_struct *mm,
                  unsigned long start, unsigned long end)
{
    if (mm_has_notifiers(mm))
        __mmu_notifier_invalidate_range_start(mm, start, end);
}

static inline void mmu_notifier_invalidate_range_end(struct mm_struct *mm,
                  unsigned long start, unsigned long end)
{
    if (mm_has_notifiers(mm))
        __mmu_notifier_invalidate_range_end(mm, start, end);
}

static inline void mmu_notifier_mm_init(struct mm_struct *mm)
{
    mm->mmu_notifier_mm = NULL;
}

static inline void mmu_notifier_mm_destroy(struct mm_struct *mm)
{
    if (mm_has_notifiers(mm))
        __mmu_notifier_mm_destroy(mm);
}

#define ptep_clear_flush_young_notify(__vma, __address, __ptep)     \
({                                  \
    int __young;                            \
    struct vm_area_struct *___vma = __vma;              \
    unsigned long ___address = __address;               \
    __young = ptep_clear_flush_young(___vma, ___address, __ptep);   \
    __young |= mmu_notifier_clear_flush_young(___vma->vm_mm,    \
                          ___address);      \
    __young;                            \
})

#define pmdp_clear_flush_young_notify(__vma, __address, __pmdp)     \
({                                  \
    int __young;                            \
    struct vm_area_struct *___vma = __vma;              \
    unsigned long ___address = __address;               \
    __young = pmdp_clear_flush_young(___vma, ___address, __pmdp);   \
    __young |= mmu_notifier_clear_flush_young(___vma->vm_mm,    \
                          ___address);      \
    __young;                            \
})

/*
 * set_pte_at_notify() sets the pte _after_ running the notifier.
 * This is safe to start by updating the secondary MMUs, because the primary MMU
 * pte invalidate must have already happened with a ptep_clear_flush() before
 * set_pte_at_notify() has been invoked.  Updating the secondary MMUs first is
 * required when we change both the protection of the mapping from read-only to
 * read-write and the pfn (like during copy on write page faults). Otherwise the
 * old page would remain mapped readonly in the secondary MMUs after the new
 * page is already writable by some CPU through the primary MMU.
 */
#define set_pte_at_notify(__mm, __address, __ptep, __pte)       \
({                                  \
    struct mm_struct *___mm = __mm;                 \
    unsigned long ___address = __address;               \
    pte_t ___pte = __pte;                       \
                                    \
    mmu_notifier_change_pte(___mm, ___address, ___pte);     \
    set_pte_at(___mm, ___address, __ptep, ___pte);          \
})

#else /* CONFIG_MMU_NOTIFIER */

static inline void mmu_notifier_release(struct mm_struct *mm)
{
}

static inline int mmu_notifier_clear_flush_young(struct mm_struct *mm,
                      unsigned long address)
{
    return 0;
}

static inline int mmu_notifier_test_young(struct mm_struct *mm,
                      unsigned long address)
{
    return 0;
}

static inline void mmu_notifier_change_pte(struct mm_struct *mm,
                       unsigned long address, pte_t pte)
{
}

static inline void mmu_notifier_invalidate_page(struct mm_struct *mm,
                      unsigned long address)
{
}

static inline void mmu_notifier_invalidate_range_start(struct mm_struct *mm,
                  unsigned long start, unsigned long end)
{
}

static inline void mmu_notifier_invalidate_range_end(struct mm_struct *mm,
                  unsigned long start, unsigned long end)
{
}

static inline void mmu_notifier_mm_init(struct mm_struct *mm)
{
}

static inline void mmu_notifier_mm_destroy(struct mm_struct *mm)
{
}

#define ptep_clear_flush_young_notify ptep_clear_flush_young
#define pmdp_clear_flush_young_notify pmdp_clear_flush_young
#define set_pte_at_notify set_pte_at

#endif /* CONFIG_MMU_NOTIFIER */

#endif /* _LINUX_MMU_NOTIFIER_H */