Re: [PATCH 01 of 12] Core of mmu notifiers

Andrea Arcangeli
2008-04-24T06:49:40Z

On Thu, Apr 24, 2008 at 12:19:28AM +0200, Andrea Arcangeli wrote:
> /dev/kvm closure. Given this can be a considered a bugfix to
> mmu_notifier_unregister I'll apply it to 1/N and I'll release a new

I'm not sure anymore this can be considered a bugfix given how large
change this resulted in the locking and register/unregister/release
behavior.

Here a full draft patch for review and testing. Works great with KVM
so far at least...

- mmu_notifier_register has to run on current->mm or on
get_task_mm() (in the later case it can mmput after
mmu_notifier_register returns)

- mmu_notifier_register in turn can't race against
mmu_notifier_release as that runs in exit_mmap after the last mmput

- mmu_notifier_unregister can run at any time, even after exit_mmap
completed. No mm_count pin is required, it's taken automatically by
register and released by unregister

- mmu_notifier_unregister serializes against all mmu notifiers with
srcu, and it serializes especially against a concurrent
mmu_notifier_unregister with a mix of a spinlock and SRCU

- the spinlock let us keep track who run first between
mmu_notifier_unregister and mmu_notifier_release, this makes life
much easier for the driver to handle as the driver is then
guaranteed that ->release will run.

- The first that runs executes ->release method as well after dropping
the spinlock but before releasing the srcu lock

- it was unsafe to unpin the module count from ->release, as release
itself has to run the 'ret' instruction to return back to the mmu
notifier code

- the ->release method is mandatory as it has to run before the pages
are freed to zap all existing sptes

- the one that arrives second between mmu_notifier_unregister and
mmu_notifier_register waits the first with srcu

As said this is a much larger change than I hoped, but as usual it can
only affect KVM/GRU/XPMEM if something is wrong with this. I don't
exclude we'll have to backoff to the previous mm_users model. The main
issue with taking a mm_users pin is that filehandles associated with
vmas aren't closed by exit() if the mm_users is pinned (that simply
leaks ram with kvm). It looks more correct not to relay on the
mm_users being >0 only in mmu_notifier_register. The other big change
is that ->release is mandatory and always called by the first between
mmu_notifier_unregister or mmu_notifier_release. Both
mmu_notifier_unregister and mmu_notifier_release are slow paths so
taking a spinlock there is no big deal.

Impact when the mmu notifiers are disarmed is unchanged.

The interesting part of the kvm patch to test this change is
below. After this last bit KVM patch status is almost final if this
new mmu notifier update is remotely ok, I've another one that does the
locking change to remove the page pin.

+static void kvm_free_vcpus(struct kvm *kvm);
+/* This must zap all the sptes because all pages will be freed then */
+static void kvm_mmu_notifier_release(struct mmu_notifier *mn,
+ struct mm_struct *mm)
+{
+ struct kvm *kvm = mmu_notifier_to_kvm(mn);
+ BUG_ON(mm != kvm->mm);
+ kvm_free_pit(kvm);
+ kfree(kvm->arch.vpic);
+ kfree(kvm->arch.vioapic);
+ kvm_free_vcpus(kvm);
+ kvm_free_physmem(kvm);
+ if (kvm->arch.apic_access_page)
+ put_page(kvm->arch.apic_access_page);
+}
+
+static const struct mmu_notifier_ops kvm_mmu_notifier_ops = {
+ .release = kvm_mmu_notifier_release,
+ .invalidate_page = kvm_mmu_notifier_invalidate_page,
+ .invalidate_range_end = kvm_mmu_notifier_invalidate_range_end,
+ .clear_flush_young = kvm_mmu_notifier_clear_flush_young,
+};
+
struct kvm *kvm_arch_create_vm(void)
{
struct kvm *kvm = kzalloc(sizeof(struct kvm), GFP_KERNEL);
+ int err;

if (!kvm)
return ERR_PTR(-ENOMEM);

INIT_LIST_HEAD(&kvm->arch.active_mmu_pages);

+ kvm->arch.mmu_notifier.ops = &kvm_mmu_notifier_ops;
+ err = mmu_notifier_register(&kvm->arch.mmu_notifier, current->mm);
+ if (err) {
+ kfree(kvm);
+ return ERR_PTR(err);
+ }
+
return kvm;
}

@@ -3899,13 +3967,12 @@ static void kvm_free_vcpus(struct kvm *kvm)

void kvm_arch_destroy_vm(struct kvm *kvm)
{
- kvm_free_pit(kvm);
- kfree(kvm->arch.vpic);
- kfree(kvm->arch.vioapic);
- kvm_free_vcpus(kvm);
- kvm_free_physmem(kvm);
- if (kvm->arch.apic_access_page)
- put_page(kvm->arch.apic_access_page);
+ /*
+ * kvm_mmu_notifier_release() will be called before
+ * mmu_notifier_unregister returns, if it didn't run
+ * already.
+ */
+ mmu_notifier_unregister(&kvm->arch.mmu_notifier, kvm->mm);
kfree(kvm);
}

Let's call this mmu notifier #v14-test1.

Signed-off-by: Andrea Arcangeli <andrea@qumranet.com>
Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Christoph Lameter <clameter@sgi.com>

diff --git a/include/linux/mm.h b/include/linux/mm.h
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1050,6 +1050,27 @@
unsigned long addr, unsigned long len,
unsigned long flags, struct page **pages);

+/*
+ * mm_lock will take mmap_sem writably (to prevent all modifications
+ * and scanning of vmas) and then also takes the mapping locks for
+ * each of the vma to lockout any scans of pagetables of this address
+ * space. This can be used to effectively holding off reclaim from the
+ * address space.
+ *
+ * mm_lock can fail if there is not enough memory to store a pointer
+ * array to all vmas.
+ *
+ * mm_lock and mm_unlock are expensive operations that may take a long time.
+ */
+struct mm_lock_data {
+ spinlock_t **i_mmap_locks;
+ spinlock_t **anon_vma_locks;
+ size_t nr_i_mmap_locks;
+ size_t nr_anon_vma_locks;
+};
+extern int mm_lock(struct mm_struct *mm, struct mm_lock_data *data);
+extern void mm_unlock(struct mm_struct *mm, struct mm_lock_data *data);
+
extern unsigned long get_unmapped_area(struct file *, unsigned long, unsigned long, unsigned long, unsigned long);

extern unsigned long do_mmap_pgoff(struct file *file, unsigned long addr,
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -19,6 +19,7 @@
#define AT_VECTOR_SIZE (2*(AT_VECTOR_SIZE_ARCH + AT_VECTOR_SIZE_BASE + 1))

struct address_space;
+struct mmu_notifier_mm;

#if NR_CPUS >= CONFIG_SPLIT_PTLOCK_CPUS
typedef atomic_long_t mm_counter_t;
@@ -225,6 +226,9 @@
#ifdef CONFIG_CGROUP_MEM_RES_CTLR
struct mem_cgroup *mem_cgroup;
#endif
+#ifdef CONFIG_MMU_NOTIFIER
+ struct mmu_notifier_mm *mmu_notifier_mm;
+#endif
};

#endif /* _LINUX_MM_TYPES_H */
diff --git a/include/linux/mmu_notifier.h b/include/linux/mmu_notifier.h
new file mode 100644
--- /dev/null
+++ b/include/linux/mmu_notifier.h
@@ -0,0 +1,251 @@
+#ifndef _LINUX_MMU_NOTIFIER_H
+#define _LINUX_MMU_NOTIFIER_H
+
+#include <linux/list.h>
+#include <linux/spinlock.h>
+#include <linux/mm_types.h>
+
+struct mmu_notifier;
+struct mmu_notifier_ops;
+
+#ifdef CONFIG_MMU_NOTIFIER
+#include <linux/srcu.h>
+
+struct mmu_notifier_mm {
+ struct hlist_head list;
+ struct srcu_struct srcu;
+ /* to serialize mmu_notifier_unregister against mmu_notifier_release */
+ spinlock_t unregister_lock;
+};
+
+struct mmu_notifier_ops {
+ /*
+ * Called after all other threads have terminated and the executing
+ * thread is the only remaining execution thread. There are no
+ * users of the mm_struct remaining.
+ *
+ * If the methods are implemented in a module, the module
+ * can't be unloaded until release() is called.
+ */
+ 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);
+
+ /*
+ * Before this is invoked any secondary MMU is still ok to
+ * read/write to the page previously pointed by the Linux pte
+ * because the old page hasn't been freed yet. 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 is held and/or
+ * the semaphores protecting the reverse maps. Both functions
+ * may sleep. The subsystem must guarantee that no additional
+ * references 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 permitted
+ * by the driver or the driver may exclude other invalidation
+ * from proceeding by blocking on new invalidate_range_start()
+ * callback that overlap invalidates that are already in
+ * progress. Either way the establishment of sptes to the
+ * range can only be allowed if all invalidate_range_stop()
+ * function have been called.
+ *
+ * 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_sem or anon_vma->sem).
+ * 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 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 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 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_notify(__vma, __address, __ptep) \
+({ \
+ pte_t __pte; \
+ struct vm_area_struct *___vma = __vma; \
+ unsigned long ___address = __address; \
+ __pte = ptep_clear_flush(___vma, ___address, __ptep); \
+ mmu_notifier_invalidate_page(___vma->vm_mm, ___address); \
+ __pte; \
+})
+
+#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; \
+})
+
+#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 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 ptep_clear_flush_notify ptep_clear_flush
+
+#endif /* CONFIG_MMU_NOTIFIER */
+
+#endif /* _LINUX_MMU_NOTIFIER_H */
diff --git a/kernel/fork.c b/kernel/fork.c
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -53,6 +53,7 @@
#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>
@@ -362,6 +363,7 @@

if (likely(!mm_alloc_pgd(mm))) {
mm->def_flags = 0;
+ mmu_notifier_mm_init(mm);
return mm;
}

@@ -395,6 +397,7 @@
BUG_ON(mm == &init_mm);
mm_free_pgd(mm);
destroy_context(mm);
+ mmu_notifier_mm_destroy(mm);
free_mm(mm);
}
EXPORT_SYMBOL_GPL(__mmdrop);
diff --git a/mm/Kconfig b/mm/Kconfig
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -193,3 +193,7 @@
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"
diff --git a/mm/Makefile b/mm/Makefile
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -33,4 +33,5 @@
obj-$(CONFIG_SMP) += allocpercpu.o
obj-$(CONFIG_QUICKLIST) += quicklist.o
obj-$(CONFIG_CGROUP_MEM_RES_CTLR) += memcontrol.o
+obj-$(CONFIG_MMU_NOTIFIER) += mmu_notifier.o

diff --git a/mm/filemap_xip.c b/mm/filemap_xip.c
--- a/mm/filemap_xip.c
+++ b/mm/filemap_xip.c
@@ -194,7 +194,7 @@
if (pte) {
/* Nuke the page table entry. */
flush_cache_page(vma, address, pte_pfn(*pte));
- pteval = ptep_clear_flush(vma, address, pte);
+ pteval = ptep_clear_flush_notify(vma, address, pte);
page_remove_rmap(page, vma);
dec_mm_counter(mm, file_rss);
BUG_ON(pte_dirty(pteval));
diff --git a/mm/fremap.c b/mm/fremap.c
--- a/mm/fremap.c
+++ b/mm/fremap.c
@@ -15,6 +15,7 @@
#include <linux/rmap.h>
#include <linux/module.h>
#include <linux/syscalls.h>
+#include <linux/mmu_notifier.h>

#include <asm/mmu_context.h>
#include <asm/cacheflush.h>
@@ -214,7 +215,9 @@
spin_unlock(&mapping->i_mmap_lock);
}

+ mmu_notifier_invalidate_range_start(mm, start, start + size);
err = populate_range(mm, vma, start, size, pgoff);
+ mmu_notifier_invalidate_range_end(mm, start, start + size);
if (!err && !(flags & MAP_NONBLOCK)) {
if (unlikely(has_write_lock)) {
downgrade_write(&mm->mmap_sem);
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -14,6 +14,7 @@
#include <linux/mempolicy.h>
#include <linux/cpuset.h>
#include <linux/mutex.h>
+#include <linux/mmu_notifier.h>

#include <asm/page.h>
#include <asm/pgtable.h>
@@ -799,6 +800,7 @@
BUG_ON(start & ~HPAGE_MASK);
BUG_ON(end & ~HPAGE_MASK);

+ mmu_notifier_invalidate_range_start(mm, start, end);
spin_lock(&mm->page_table_lock);
for (address = start; address < end; address += HPAGE_SIZE) {
ptep = huge_pte_offset(mm, address);
@@ -819,6 +821,7 @@
}
spin_unlock(&mm->page_table_lock);
flush_tlb_range(vma, start, end);
+ mmu_notifier_invalidate_range_end(mm, start, end);
list_for_each_entry_safe(page, tmp, &page_list, lru) {
list_del(&page->lru);
put_page(page);
diff --git a/mm/memory.c b/mm/memory.c
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -51,6 +51,7 @@
#include <linux/init.h>
#include <linux/writeback.h>
#include <linux/memcontrol.h>
+#include <linux/mmu_notifier.h>

#include <asm/pgalloc.h>
#include <asm/uaccess.h>
@@ -596,6 +597,7 @@
unsigned long next;
unsigned long addr = vma->vm_start;
unsigned long end = vma->vm_end;
+ int ret;

/*
* Don't copy ptes where a page fault will fill them correctly.
@@ -603,25 +605,39 @@
* readonly mappings. The tradeoff is that copy_page_range is more
* efficient than faulting.
*/
+ ret = 0;
if (!(vma->vm_flags & (VM_HUGETLB|VM_NONLINEAR|VM_PFNMAP|VM_INSERTPAGE))) {
if (!vma->anon_vma)
- return 0;
+ goto out;
}

- if (is_vm_hugetlb_page(vma))
- return copy_hugetlb_page_range(dst_mm, src_mm, vma);
+ if (unlikely(is_vm_hugetlb_page(vma))) {
+ ret = copy_hugetlb_page_range(dst_mm, src_mm, vma);
+ goto out;
+ }

+ if (is_cow_mapping(vma->vm_flags))
+ mmu_notifier_invalidate_range_start(src_mm, addr, end);
+
+ ret = 0;
dst_pgd = pgd_offset(dst_mm, addr);
src_pgd = pgd_offset(src_mm, addr);
do {
next = pgd_addr_end(addr, end);
if (pgd_none_or_clear_bad(src_pgd))
continue;
- if (copy_pud_range(dst_mm, src_mm, dst_pgd, src_pgd,
- vma, addr, next))
- return -ENOMEM;
+ if (unlikely(copy_pud_range(dst_mm, src_mm, dst_pgd, src_pgd,
+ vma, addr, next))) {
+ ret = -ENOMEM;
+ break;
+ }
} while (dst_pgd++, src_pgd++, addr = next, addr != end);
- return 0;
+
+ if (is_cow_mapping(vma->vm_flags))
+ mmu_notifier_invalidate_range_end(src_mm,
+ vma->vm_start, end);
+out:
+ return ret;
}

static unsigned long zap_pte_range(struct mmu_gather *tlb,
@@ -825,7 +841,9 @@
unsigned long start = start_addr;
spinlock_t *i_mmap_lock = details? details->i_mmap_lock: NULL;
int fullmm = (*tlbp)->fullmm;
+ struct mm_struct *mm = vma->vm_mm;

+ mmu_notifier_invalidate_range_start(mm, start_addr, end_addr);
for ( ; vma && vma->vm_start < end_addr; vma = vma->vm_next) {
unsigned long end;

@@ -876,6 +894,7 @@
}
}
out:
+ mmu_notifier_invalidate_range_end(mm, start_addr, end_addr);
return start; /* which is now the end (or restart) address */
}

@@ -1463,10 +1482,11 @@
{
pgd_t *pgd;
unsigned long next;
- unsigned long end = addr + size;
+ unsigned long start = addr, end = addr + size;
int err;

BUG_ON(addr >= end);
+ mmu_notifier_invalidate_range_start(mm, start, end);
pgd = pgd_offset(mm, addr);
do {
next = pgd_addr_end(addr, end);
@@ -1474,6 +1494,7 @@
if (err)
break;
} while (pgd++, addr = next, addr != end);
+ mmu_notifier_invalidate_range_end(mm, start, end);
return err;
}
EXPORT_SYMBOL_GPL(apply_to_page_range);
@@ -1675,7 +1696,7 @@
* seen in the presence of one thread doing SMC and another
* thread doing COW.
*/
- ptep_clear_flush(vma, address, page_table);
+ ptep_clear_flush_notify(vma, address, page_table);
set_pte_at(mm, address, page_table, entry);
update_mmu_cache(vma, address, entry);
lru_cache_add_active(new_page);
diff --git a/mm/mmap.c b/mm/mmap.c
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -26,6 +26,9 @@
#include <linux/mount.h>
#include <linux/mempolicy.h>
#include <linux/rmap.h>
+#include <linux/vmalloc.h>
+#include <linux/sort.h>
+#include <linux/mmu_notifier.h>

#include <asm/uaccess.h>
#include <asm/cacheflush.h>
@@ -2038,6 +2041,7 @@

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

lru_add_drain();
flush_cache_mm(mm);
@@ -2242,3 +2246,144 @@

return 0;
}
+
+static int mm_lock_cmp(const void *a, const void *b)
+{
+ unsigned long _a = (unsigned long)*(spinlock_t **)a;
+ unsigned long _b = (unsigned long)*(spinlock_t **)b;
+
+ cond_resched();
+ if (_a < _b)
+ return -1;
+ if (_a > _b)
+ return 1;
+ return 0;
+}
+
+static unsigned long mm_lock_sort(struct mm_struct *mm, spinlock_t **locks,
+ int anon)
+{
+ struct vm_area_struct *vma;
+ size_t i = 0;
+
+ for (vma = mm->mmap; vma; vma = vma->vm_next) {
+ if (anon) {
+ if (vma->anon_vma)
+ locks[i++] = &vma->anon_vma->lock;
+ } else {
+ if (vma->vm_file && vma->vm_file->f_mapping)
+ locks[i++] = &vma->vm_file->f_mapping->i_mmap_lock;
+ }
+ }
+
+ if (!i)
+ goto out;
+
+ sort(locks, i, sizeof(spinlock_t *), mm_lock_cmp, NULL);
+
+out:
+ return i;
+}
+
+static inline unsigned long mm_lock_sort_anon_vma(struct mm_struct *mm,
+ spinlock_t **locks)
+{
+ return mm_lock_sort(mm, locks, 1);
+}
+
+static inline unsigned long mm_lock_sort_i_mmap(struct mm_struct *mm,
+ spinlock_t **locks)
+{
+ return mm_lock_sort(mm, locks, 0);
+}
+
+static void mm_lock_unlock(spinlock_t **locks, size_t nr, int lock)
+{
+ spinlock_t *last = NULL;
+ size_t i;
+
+ for (i = 0; i < nr; i++)
+ /* Multiple vmas may use the same lock. */
+ if (locks[i] != last) {
+ BUG_ON((unsigned long) last > (unsigned long) locks[i]);
+ last = locks[i];
+ if (lock)
+ spin_lock(last);
+ else
+ spin_unlock(last);
+ }
+}
+
+static inline void __mm_lock(spinlock_t **locks, size_t nr)
+{
+ mm_lock_unlock(locks, nr, 1);
+}
+
+static inline void __mm_unlock(spinlock_t **locks, size_t nr)
+{
+ mm_lock_unlock(locks, nr, 0);
+}
+
+/*
+ * This operation locks against the VM for all pte/vma/mm related
+ * operations that could ever happen on a certain mm. This includes
+ * vmtruncate, try_to_unmap, and all page faults. The holder
+ * must not hold any mm related lock. A single task can't take more
+ * than one mm lock in a row or it would deadlock.
+ */
+int mm_lock(struct mm_struct *mm, struct mm_lock_data *data)
+{
+ spinlock_t **anon_vma_locks, **i_mmap_locks;
+
+ down_write(&mm->mmap_sem);
+ if (mm->map_count) {
+ anon_vma_locks = vmalloc(sizeof(spinlock_t *) * mm->map_count);
+ if (unlikely(!anon_vma_locks)) {
+ up_write(&mm->mmap_sem);
+ return -ENOMEM;
+ }
+
+ i_mmap_locks = vmalloc(sizeof(spinlock_t *) * mm->map_count);
+ if (unlikely(!i_mmap_locks)) {
+ up_write(&mm->mmap_sem);
+ vfree(anon_vma_locks);
+ return -ENOMEM;
+ }
+
+ data->nr_anon_vma_locks = mm_lock_sort_anon_vma(mm, anon_vma_locks);
+ data->nr_i_mmap_locks = mm_lock_sort_i_mmap(mm, i_mmap_locks);
+
+ if (data->nr_anon_vma_locks) {
+ __mm_lock(anon_vma_locks, data->nr_anon_vma_locks);
+ data->anon_vma_locks = anon_vma_locks;
+ } else
+ vfree(anon_vma_locks);
+
+ if (data->nr_i_mmap_locks) {
+ __mm_lock(i_mmap_locks, data->nr_i_mmap_locks);
+ data->i_mmap_locks = i_mmap_locks;
+ } else
+ vfree(i_mmap_locks);
+ }
+ return 0;
+}
+
+static void mm_unlock_vfree(spinlock_t **locks, size_t nr)
+{
+ __mm_unlock(locks, nr);
+ vfree(locks);
+}
+
+/* avoid memory allocations for mm_unlock to prevent deadlock */
+void mm_unlock(struct mm_struct *mm, struct mm_lock_data *data)
+{
+ if (mm->map_count) {
+ if (data->nr_anon_vma_locks)
+ mm_unlock_vfree(data->anon_vma_locks,
+ data->nr_anon_vma_locks);
+ if (data->i_mmap_locks)
+ mm_unlock_vfree(data->i_mmap_locks,
+ data->nr_i_mmap_locks);
+ }
+ up_write(&mm->mmap_sem);
+}
diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c
new file mode 100644
--- /dev/null
+++ b/mm/mmu_notifier.c
@@ -0,0 +1,241 @@
+/*
+ * linux/mm/mmu_notifier.c
+ *
+ * Copyright (C) 2008 Qumranet, Inc.
+ * Copyright (C) 2008 SGI
+ * Christoph Lameter <clameter@sgi.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2. See
+ * the COPYING file in the top-level directory.
+ */
+
+#include <linux/mmu_notifier.h>
+#include <linux/module.h>
+#include <linux/mm.h>
+#include <linux/err.h>
+#include <linux/srcu.h>
+#include <linux/rcupdate.h>
+#include <linux/sched.h>
+
+/*
+ * This function can't run concurrently against mmu_notifier_register
+ * or any other mmu notifier method. mmu_notifier_register can only
+ * run with mm->mm_users > 0 (and exit_mmap runs only when mm_users is
+ * zero). All other tasks of this mm already quit so they can't invoke
+ * mmu notifiers anymore. This can run concurrently only against
+ * mmu_notifier_unregister and it serializes against it with the
+ * unregister_lock in addition to RCU. struct mmu_notifier_mm can't go
+ * away from under us as the exit_mmap holds a mm_count pin itself.
+ *
+ * The ->release method can't allow the module to be unloaded, the
+ * module can only be unloaded after mmu_notifier_unregister run. This
+ * is because the release method has to run the ret instruction to
+ * return back here, and so it can't allow the ret instruction to be
+ * freed.
+ */
+void __mmu_notifier_release(struct mm_struct *mm)
+{
+ struct mmu_notifier *mn;
+ int srcu;
+
+ srcu = srcu_read_lock(&mm->mmu_notifier_mm->srcu);
+ spin_lock(&mm->mmu_notifier_mm->unregister_lock);
+ while (unlikely(!hlist_empty(&mm->mmu_notifier_mm->list))) {
+ mn = hlist_entry(mm->mmu_notifier_mm->list.first,
+ struct mmu_notifier,
+ hlist);
+ /*
+ * We arrived before mmu_notifier_unregister so
+ * mmu_notifier_unregister will do nothing else than
+ * to wait ->release to finish and
+ * mmu_notifier_unregister to return.
+ */
+ hlist_del_init(&mn->hlist);
+ /*
+ * if ->release runs before mmu_notifier_unregister it
+ * must be handled as it's the only way for the driver
+ * to flush all existing sptes before the pages in the
+ * mm are freed.
+ */
+ spin_unlock(&mm->mmu_notifier_mm->unregister_lock);
+ /* SRCU will block mmu_notifier_unregister */
+ mn->ops->release(mn, mm);
+ spin_lock(&mm->mmu_notifier_mm->unregister_lock);
+ }
+ spin_unlock(&mm->mmu_notifier_mm->unregister_lock);
+ srcu_read_unlock(&mm->mmu_notifier_mm->srcu, srcu);
+
+ /*
+ * Wait ->release if mmu_notifier_unregister run list_del_rcu.
+ * srcu can't go away from under us because one mm_count is
+ * hold by exit_mmap.
+ */
+ synchronize_srcu(&mm->mmu_notifier_mm->srcu);
+}
+
+/*
+ * If no young bitflag is supported by the hardware, ->clear_flush_young can
+ * unmap the address and return 1 or 0 depending if the mapping previously
+ * existed or not.
+ */
+int __mmu_notifier_clear_flush_young(struct mm_struct *mm,
+ unsigned long address)
+{
+ struct mmu_notifier *mn;
+ struct hlist_node *n;
+ int young = 0, srcu;
+
+ srcu = srcu_read_lock(&mm->mmu_notifier_mm->srcu);
+ hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
+ if (mn->ops->clear_flush_young)
+ young |= mn->ops->clear_flush_young(mn, mm, address);
+ }
+ srcu_read_unlock(&mm->mmu_notifier_mm->srcu, srcu);
+
+ return young;
+}
+
+void __mmu_notifier_invalidate_page(struct mm_struct *mm,
+ unsigned long address)
+{
+ struct mmu_notifier *mn;
+ struct hlist_node *n;
+ int srcu;
+
+ srcu = srcu_read_lock(&mm->mmu_notifier_mm->srcu);
+ hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
+ if (mn->ops->invalidate_page)
+ mn->ops->invalidate_page(mn, mm, address);
+ }
+ srcu_read_unlock(&mm->mmu_notifier_mm->srcu, srcu);
+}
+
+void __mmu_notifier_invalidate_range_start(struct mm_struct *mm,
+ unsigned long start, unsigned long end)
+{
+ struct mmu_notifier *mn;
+ struct hlist_node *n;
+ int srcu;
+
+ srcu = srcu_read_lock(&mm->mmu_notifier_mm->srcu);
+ hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
+ if (mn->ops->invalidate_range_start)
+ mn->ops->invalidate_range_start(mn, mm, start, end);
+ }
+ srcu_read_unlock(&mm->mmu_notifier_mm->srcu, srcu);
+}
+
+void __mmu_notifier_invalidate_range_end(struct mm_struct *mm,
+ unsigned long start, unsigned long end)
+{
+ struct mmu_notifier *mn;
+ struct hlist_node *n;
+ int srcu;
+
+ srcu = srcu_read_lock(&mm->mmu_notifier_mm->srcu);
+ hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
+ if (mn->ops->invalidate_range_end)
+ mn->ops->invalidate_range_end(mn, mm, start, end);
+ }
+ srcu_read_unlock(&mm->mmu_notifier_mm->srcu, srcu);
+}
+
+/*
+ * Must not hold mmap_sem nor any other VM related lock when calling
+ * this registration function. Must also ensure mm_users can't go down
+ * to zero while this runs to avoid races with mmu_notifier_release,
+ * so mm has to be current->mm or the mm should be pinned safely like
+ * with get_task_mm(). mmput can be called after mmu_notifier_register
+ * returns. mmu_notifier_unregister must be always called to
+ * unregister the notifier. mm_count is automatically pinned to allow
+ * mmu_notifier_unregister to safely run at any time later, before or
+ * after exit_mmap. ->release will always be called before exit_mmap
+ * frees the pages.
+ */
+int mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
+{
+ struct mm_lock_data data;
+ int ret;
+
+ BUG_ON(atomic_read(&mm->mm_users) <= 0);
+
+ ret = mm_lock(mm, &data);
+ if (unlikely(ret))
+ goto out;
+
+ if (!mm_has_notifiers(mm)) {
+ mm->mmu_notifier_mm = kmalloc(sizeof(struct mmu_notifier_mm),
+ GFP_KERNEL);
+ ret = -ENOMEM;
+ if (unlikely(!mm_has_notifiers(mm)))
+ goto out_unlock;
+
+ ret = init_srcu_struct(&mm->mmu_notifier_mm->srcu);
+ if (unlikely(ret)) {
+ kfree(mm->mmu_notifier_mm);
+ mmu_notifier_mm_init(mm);
+ goto out_unlock;
+ }
+ INIT_HLIST_HEAD(&mm->mmu_notifier_mm->list);
+ spin_lock_init(&mm->mmu_notifier_mm->unregister_lock);
+ }
+ atomic_inc(&mm->mm_count);
+
+ hlist_add_head_rcu(&mn->hlist, &mm->mmu_notifier_mm->list);
+out_unlock:
+ mm_unlock(mm, &data);
+out:
+ BUG_ON(atomic_read(&mm->mm_users) <= 0);
+ return ret;
+}
+EXPORT_SYMBOL_GPL(mmu_notifier_register);
+
+/* this is called after the last mmu_notifier_unregister() returned */
+void __mmu_notifier_mm_destroy(struct mm_struct *mm)
+{
+ BUG_ON(!hlist_empty(&mm->mmu_notifier_mm->list));
+ cleanup_srcu_struct(&mm->mmu_notifier_mm->srcu);
+ kfree(mm->mmu_notifier_mm);
+ mm->mmu_notifier_mm = LIST_POISON1; /* debug */
+}
+
+/*
+ * This releases the mm_count pin automatically and frees the mm
+ * structure if it was the last user of it. It serializes against
+ * running mmu notifiers with SRCU and against mmu_notifier_unregister
+ * with the unregister lock + SRCU. All sptes must be dropped before
+ * calling mmu_notifier_unregister. ->release or any other notifier
+ * method may be invoked concurrently with mmu_notifier_unregister,
+ * and only after mmu_notifier_unregister returned we're guaranteed
+ * that ->release or any other method can't run anymore.
+ */
+void mmu_notifier_unregister(struct mmu_notifier *mn, struct mm_struct *mm)
+{
+ int before_release = 0, srcu;
+
+ BUG_ON(atomic_read(&mm->mm_count) <= 0);
+
+ srcu = srcu_read_lock(&mm->mmu_notifier_mm->srcu);
+ spin_lock(&mm->mmu_notifier_mm->unregister_lock);
+ if (!hlist_unhashed(&mn->hlist)) {
+ hlist_del_rcu(&mn->hlist);
+ before_release = 1;
+ }
+ spin_unlock(&mm->mmu_notifier_mm->unregister_lock);
+ if (before_release)
+ /*
+ * exit_mmap will block in mmu_notifier_release to
+ * guarantee ->release is called before freeing the
+ * pages.
+ */
+ mn->ops->release(mn, mm);
+ srcu_read_unlock(&mm->mmu_notifier_mm->srcu, srcu);
+
+ /* wait any running method to finish, including ->release */
+ synchronize_srcu(&mm->mmu_notifier_mm->srcu);
+
+ BUG_ON(atomic_read(&mm->mm_count) <= 0);
+
+ mmdrop(mm);
+}
+EXPORT_SYMBOL_GPL(mmu_notifier_unregister);
diff --git a/mm/mprotect.c b/mm/mprotect.c
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -21,6 +21,7 @@
#include <linux/syscalls.h>
#include <linux/swap.h>
#include <linux/swapops.h>
+#include <linux/mmu_notifier.h>
#include <asm/uaccess.h>
#include <asm/pgtable.h>
#include <asm/cacheflush.h>
@@ -198,10 +199,12 @@
dirty_accountable = 1;
}

+ mmu_notifier_invalidate_range_start(mm, start, end);
if (is_vm_hugetlb_page(vma))
hugetlb_change_protection(vma, start, end, vma->vm_page_prot);
else
change_protection(vma, start, end, vma->vm_page_prot, dirty_accountable);
+ mmu_notifier_invalidate_range_end(mm, start, end);
vm_stat_account(mm, oldflags, vma->vm_file, -nrpages);
vm_stat_account(mm, newflags, vma->vm_file, nrpages);
return 0;
diff --git a/mm/mremap.c b/mm/mremap.c
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -18,6 +18,7 @@
#include <linux/highmem.h>
#include <linux/security.h>
#include <linux/syscalls.h>
+#include <linux/mmu_notifier.h>

#include <asm/uaccess.h>
#include <asm/cacheflush.h>
@@ -74,7 +75,11 @@
struct mm_struct *mm = vma->vm_mm;
pte_t *old_pte, *new_pte, pte;
spinlock_t *old_ptl, *new_ptl;
+ unsigned long old_start;

+ old_start = old_addr;
+ mmu_notifier_invalidate_range_start(vma->vm_mm,
+ old_start, old_end);
if (vma->vm_file) {
/*
* Subtle point from Rajesh Venkatasubramanian: before
@@ -116,6 +121,7 @@
pte_unmap_unlock(old_pte - 1, old_ptl);
if (mapping)
spin_unlock(&mapping->i_mmap_lock);
+ mmu_notifier_invalidate_range_end(vma->vm_mm, old_start, old_end);
}

#define LATENCY_LIMIT (64 * PAGE_SIZE)
diff --git a/mm/rmap.c b/mm/rmap.c
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -49,6 +49,7 @@
#include <linux/module.h>
#include <linux/kallsyms.h>
#include <linux/memcontrol.h>
+#include <linux/mmu_notifier.h>

#include <asm/tlbflush.h>

@@ -287,7 +288,7 @@
if (vma->vm_flags & VM_LOCKED) {
referenced++;
*mapcount = 1; /* break early from loop */
- } else if (ptep_clear_flush_young(vma, address, pte))
+ } else if (ptep_clear_flush_young_notify(vma, address, pte))
referenced++;

/* Pretend the page is referenced if the task has the
@@ -456,7 +457,7 @@
pte_t entry;

flush_cache_page(vma, address, pte_pfn(*pte));
- entry = ptep_clear_flush(vma, address, pte);
+ entry = ptep_clear_flush_notify(vma, address, pte);
entry = pte_wrprotect(entry);
entry = pte_mkclean(entry);
set_pte_at(mm, address, pte, entry);
@@ -717,14 +718,14 @@
* skipped over this mm) then we should reactivate it.
*/
if (!migration && ((vma->vm_flags & VM_LOCKED) ||
- (ptep_clear_flush_young(vma, address, pte)))) {
+ (ptep_clear_flush_young_notify(vma, address, pte)))) {
ret = SWAP_FAIL;
goto out_unmap;
}

/* Nuke the page table entry. */
flush_cache_page(vma, address, page_to_pfn(page));
- pteval = ptep_clear_flush(vma, address, pte);
+ pteval = ptep_clear_flush_notify(vma, address, pte);

/* Move the dirty bit to the physical page now the pte is gone. */
if (pte_dirty(pteval))
@@ -849,12 +850,12 @@
page = vm_normal_page(vma, address, *pte);
BUG_ON(!page || PageAnon(page));

- if (ptep_clear_flush_young(vma, address, pte))
+ if (ptep_clear_flush_young_notify(vma, address, pte))
continue;

/* Nuke the page table entry. */
flush_cache_page(vma, address, pte_pfn(*pte));
- pteval = ptep_clear_flush(vma, address, pte);
+ pteval = ptep_clear_flush_notify(vma, address, pte);

/* If nonlinear, store the file page offset in the pte. */
if (page->index != linear_page_index(vma, address))

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