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![Daniel Vetter](/assets/img/avatar_default.png)
We need to make sure implementations don't cheat and don't have a possible schedule/blocking point deeply burried where review can't catch it. I'm not sure whether this is the best way to make sure all the might_sleep() callsites trigger, and it's a bit ugly in the code flow. But it gets the job done. Inspired by an i915 patch series which did exactly that, because the rules haven't been entirely clear to us. Link: https://lore.kernel.org/r/20190826201425.17547-5-daniel.vetter@ffwll.ch Reviewed-by: Christian König <christian.koenig@amd.com> (v1) Reviewed-by: Jérôme Glisse <jglisse@redhat.com> (v4) Signed-off-by: Daniel Vetter <daniel.vetter@intel.com> Reviewed-by: Jason Gunthorpe <jgg@mellanox.com> Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
546 lines
16 KiB
C
546 lines
16 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* linux/mm/mmu_notifier.c
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*
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* Copyright (C) 2008 Qumranet, Inc.
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* Copyright (C) 2008 SGI
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* Christoph Lameter <cl@linux.com>
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*/
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#include <linux/rculist.h>
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#include <linux/mmu_notifier.h>
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#include <linux/export.h>
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#include <linux/mm.h>
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#include <linux/err.h>
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#include <linux/srcu.h>
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#include <linux/rcupdate.h>
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#include <linux/sched.h>
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#include <linux/sched/mm.h>
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#include <linux/slab.h>
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/* global SRCU for all MMs */
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DEFINE_STATIC_SRCU(srcu);
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#ifdef CONFIG_LOCKDEP
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struct lockdep_map __mmu_notifier_invalidate_range_start_map = {
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.name = "mmu_notifier_invalidate_range_start"
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};
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#endif
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/*
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* This function can't run concurrently against mmu_notifier_register
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* because mm->mm_users > 0 during mmu_notifier_register and exit_mmap
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* runs with mm_users == 0. Other tasks may still invoke mmu notifiers
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* in parallel despite there being no task using this mm any more,
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* through the vmas outside of the exit_mmap context, such as with
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* vmtruncate. This serializes against mmu_notifier_unregister with
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* the mmu_notifier_mm->lock in addition to SRCU and it serializes
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* against the other mmu notifiers with SRCU. struct mmu_notifier_mm
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* can't go away from under us as exit_mmap holds an mm_count pin
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* itself.
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*/
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void __mmu_notifier_release(struct mm_struct *mm)
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{
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struct mmu_notifier *mn;
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int id;
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/*
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* SRCU here will block mmu_notifier_unregister until
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* ->release returns.
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*/
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id = srcu_read_lock(&srcu);
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hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist)
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/*
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* If ->release runs before mmu_notifier_unregister it must be
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* handled, as it's the only way for the driver to flush all
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* existing sptes and stop the driver from establishing any more
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* sptes before all the pages in the mm are freed.
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*/
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if (mn->ops->release)
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mn->ops->release(mn, mm);
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spin_lock(&mm->mmu_notifier_mm->lock);
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while (unlikely(!hlist_empty(&mm->mmu_notifier_mm->list))) {
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mn = hlist_entry(mm->mmu_notifier_mm->list.first,
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struct mmu_notifier,
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hlist);
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/*
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* We arrived before mmu_notifier_unregister so
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* mmu_notifier_unregister will do nothing other than to wait
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* for ->release to finish and for mmu_notifier_unregister to
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* return.
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*/
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hlist_del_init_rcu(&mn->hlist);
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}
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spin_unlock(&mm->mmu_notifier_mm->lock);
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srcu_read_unlock(&srcu, id);
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/*
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* synchronize_srcu here prevents mmu_notifier_release from returning to
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* exit_mmap (which would proceed with freeing all pages in the mm)
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* until the ->release method returns, if it was invoked by
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* mmu_notifier_unregister.
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*
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* The mmu_notifier_mm can't go away from under us because one mm_count
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* is held by exit_mmap.
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*/
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synchronize_srcu(&srcu);
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}
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/*
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* If no young bitflag is supported by the hardware, ->clear_flush_young can
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* unmap the address and return 1 or 0 depending if the mapping previously
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* existed or not.
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*/
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int __mmu_notifier_clear_flush_young(struct mm_struct *mm,
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unsigned long start,
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unsigned long end)
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{
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struct mmu_notifier *mn;
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int young = 0, id;
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id = srcu_read_lock(&srcu);
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hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
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if (mn->ops->clear_flush_young)
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young |= mn->ops->clear_flush_young(mn, mm, start, end);
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}
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srcu_read_unlock(&srcu, id);
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return young;
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}
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int __mmu_notifier_clear_young(struct mm_struct *mm,
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unsigned long start,
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unsigned long end)
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{
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struct mmu_notifier *mn;
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int young = 0, id;
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id = srcu_read_lock(&srcu);
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hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
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if (mn->ops->clear_young)
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young |= mn->ops->clear_young(mn, mm, start, end);
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}
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srcu_read_unlock(&srcu, id);
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return young;
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}
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int __mmu_notifier_test_young(struct mm_struct *mm,
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unsigned long address)
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{
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struct mmu_notifier *mn;
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int young = 0, id;
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id = srcu_read_lock(&srcu);
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hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
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if (mn->ops->test_young) {
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young = mn->ops->test_young(mn, mm, address);
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if (young)
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break;
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}
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}
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srcu_read_unlock(&srcu, id);
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return young;
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}
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void __mmu_notifier_change_pte(struct mm_struct *mm, unsigned long address,
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pte_t pte)
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{
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struct mmu_notifier *mn;
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int id;
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id = srcu_read_lock(&srcu);
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hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
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if (mn->ops->change_pte)
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mn->ops->change_pte(mn, mm, address, pte);
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}
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srcu_read_unlock(&srcu, id);
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}
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int __mmu_notifier_invalidate_range_start(struct mmu_notifier_range *range)
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{
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struct mmu_notifier *mn;
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int ret = 0;
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int id;
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id = srcu_read_lock(&srcu);
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hlist_for_each_entry_rcu(mn, &range->mm->mmu_notifier_mm->list, hlist) {
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if (mn->ops->invalidate_range_start) {
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int _ret;
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if (!mmu_notifier_range_blockable(range))
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non_block_start();
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_ret = mn->ops->invalidate_range_start(mn, range);
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if (!mmu_notifier_range_blockable(range))
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non_block_end();
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if (_ret) {
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pr_info("%pS callback failed with %d in %sblockable context.\n",
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mn->ops->invalidate_range_start, _ret,
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!mmu_notifier_range_blockable(range) ? "non-" : "");
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WARN_ON(mmu_notifier_range_blockable(range) ||
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ret != -EAGAIN);
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ret = _ret;
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}
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}
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}
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srcu_read_unlock(&srcu, id);
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return ret;
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}
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void __mmu_notifier_invalidate_range_end(struct mmu_notifier_range *range,
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bool only_end)
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{
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struct mmu_notifier *mn;
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int id;
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lock_map_acquire(&__mmu_notifier_invalidate_range_start_map);
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id = srcu_read_lock(&srcu);
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hlist_for_each_entry_rcu(mn, &range->mm->mmu_notifier_mm->list, hlist) {
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/*
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* Call invalidate_range here too to avoid the need for the
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* subsystem of having to register an invalidate_range_end
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* call-back when there is invalidate_range already. Usually a
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* subsystem registers either invalidate_range_start()/end() or
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* invalidate_range(), so this will be no additional overhead
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* (besides the pointer check).
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*
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* We skip call to invalidate_range() if we know it is safe ie
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* call site use mmu_notifier_invalidate_range_only_end() which
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* is safe to do when we know that a call to invalidate_range()
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* already happen under page table lock.
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*/
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if (!only_end && mn->ops->invalidate_range)
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mn->ops->invalidate_range(mn, range->mm,
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range->start,
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range->end);
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if (mn->ops->invalidate_range_end) {
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if (!mmu_notifier_range_blockable(range))
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non_block_start();
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mn->ops->invalidate_range_end(mn, range);
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if (!mmu_notifier_range_blockable(range))
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non_block_end();
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}
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}
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srcu_read_unlock(&srcu, id);
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lock_map_release(&__mmu_notifier_invalidate_range_start_map);
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}
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void __mmu_notifier_invalidate_range(struct mm_struct *mm,
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unsigned long start, unsigned long end)
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{
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struct mmu_notifier *mn;
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int id;
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id = srcu_read_lock(&srcu);
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hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
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if (mn->ops->invalidate_range)
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mn->ops->invalidate_range(mn, mm, start, end);
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}
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srcu_read_unlock(&srcu, id);
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}
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/*
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* Same as mmu_notifier_register but here the caller must hold the
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* mmap_sem in write mode.
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*/
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int __mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
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{
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struct mmu_notifier_mm *mmu_notifier_mm = NULL;
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int ret;
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lockdep_assert_held_write(&mm->mmap_sem);
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BUG_ON(atomic_read(&mm->mm_users) <= 0);
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if (IS_ENABLED(CONFIG_LOCKDEP)) {
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fs_reclaim_acquire(GFP_KERNEL);
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lock_map_acquire(&__mmu_notifier_invalidate_range_start_map);
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lock_map_release(&__mmu_notifier_invalidate_range_start_map);
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fs_reclaim_release(GFP_KERNEL);
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}
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mn->mm = mm;
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mn->users = 1;
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if (!mm->mmu_notifier_mm) {
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/*
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* kmalloc cannot be called under mm_take_all_locks(), but we
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* know that mm->mmu_notifier_mm can't change while we hold
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* the write side of the mmap_sem.
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*/
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mmu_notifier_mm =
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kmalloc(sizeof(struct mmu_notifier_mm), GFP_KERNEL);
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if (!mmu_notifier_mm)
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return -ENOMEM;
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INIT_HLIST_HEAD(&mmu_notifier_mm->list);
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spin_lock_init(&mmu_notifier_mm->lock);
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}
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ret = mm_take_all_locks(mm);
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if (unlikely(ret))
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goto out_clean;
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/* Pairs with the mmdrop in mmu_notifier_unregister_* */
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mmgrab(mm);
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/*
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* Serialize the update against mmu_notifier_unregister. A
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* side note: mmu_notifier_release can't run concurrently with
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* us because we hold the mm_users pin (either implicitly as
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* current->mm or explicitly with get_task_mm() or similar).
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* We can't race against any other mmu notifier method either
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* thanks to mm_take_all_locks().
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*/
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if (mmu_notifier_mm)
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mm->mmu_notifier_mm = mmu_notifier_mm;
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spin_lock(&mm->mmu_notifier_mm->lock);
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hlist_add_head_rcu(&mn->hlist, &mm->mmu_notifier_mm->list);
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spin_unlock(&mm->mmu_notifier_mm->lock);
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mm_drop_all_locks(mm);
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BUG_ON(atomic_read(&mm->mm_users) <= 0);
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return 0;
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out_clean:
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kfree(mmu_notifier_mm);
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return ret;
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}
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EXPORT_SYMBOL_GPL(__mmu_notifier_register);
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/**
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* mmu_notifier_register - Register a notifier on a mm
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* @mn: The notifier to attach
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* @mm: The mm to attach the notifier to
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*
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* Must not hold mmap_sem nor any other VM related lock when calling
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* this registration function. Must also ensure mm_users can't go down
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* to zero while this runs to avoid races with mmu_notifier_release,
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* so mm has to be current->mm or the mm should be pinned safely such
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* as with get_task_mm(). If the mm is not current->mm, the mm_users
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* pin should be released by calling mmput after mmu_notifier_register
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* returns.
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*
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* mmu_notifier_unregister() or mmu_notifier_put() must be always called to
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* unregister the notifier.
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*
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* While the caller has a mmu_notifier get the mn->mm pointer will remain
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* valid, and can be converted to an active mm pointer via mmget_not_zero().
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*/
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int mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
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{
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int ret;
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down_write(&mm->mmap_sem);
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ret = __mmu_notifier_register(mn, mm);
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up_write(&mm->mmap_sem);
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return ret;
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}
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EXPORT_SYMBOL_GPL(mmu_notifier_register);
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static struct mmu_notifier *
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find_get_mmu_notifier(struct mm_struct *mm, const struct mmu_notifier_ops *ops)
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{
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struct mmu_notifier *mn;
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spin_lock(&mm->mmu_notifier_mm->lock);
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hlist_for_each_entry_rcu (mn, &mm->mmu_notifier_mm->list, hlist) {
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if (mn->ops != ops)
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continue;
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if (likely(mn->users != UINT_MAX))
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mn->users++;
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else
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mn = ERR_PTR(-EOVERFLOW);
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spin_unlock(&mm->mmu_notifier_mm->lock);
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return mn;
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}
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spin_unlock(&mm->mmu_notifier_mm->lock);
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return NULL;
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}
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/**
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* mmu_notifier_get_locked - Return the single struct mmu_notifier for
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* the mm & ops
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* @ops: The operations struct being subscribe with
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* @mm : The mm to attach notifiers too
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*
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* This function either allocates a new mmu_notifier via
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* ops->alloc_notifier(), or returns an already existing notifier on the
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* list. The value of the ops pointer is used to determine when two notifiers
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* are the same.
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*
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* Each call to mmu_notifier_get() must be paired with a call to
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* mmu_notifier_put(). The caller must hold the write side of mm->mmap_sem.
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*
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* While the caller has a mmu_notifier get the mm pointer will remain valid,
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* and can be converted to an active mm pointer via mmget_not_zero().
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*/
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struct mmu_notifier *mmu_notifier_get_locked(const struct mmu_notifier_ops *ops,
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struct mm_struct *mm)
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{
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struct mmu_notifier *mn;
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int ret;
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lockdep_assert_held_write(&mm->mmap_sem);
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if (mm->mmu_notifier_mm) {
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mn = find_get_mmu_notifier(mm, ops);
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if (mn)
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return mn;
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}
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mn = ops->alloc_notifier(mm);
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if (IS_ERR(mn))
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return mn;
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mn->ops = ops;
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ret = __mmu_notifier_register(mn, mm);
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if (ret)
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goto out_free;
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return mn;
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out_free:
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mn->ops->free_notifier(mn);
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return ERR_PTR(ret);
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}
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EXPORT_SYMBOL_GPL(mmu_notifier_get_locked);
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/* this is called after the last mmu_notifier_unregister() returned */
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void __mmu_notifier_mm_destroy(struct mm_struct *mm)
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{
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BUG_ON(!hlist_empty(&mm->mmu_notifier_mm->list));
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kfree(mm->mmu_notifier_mm);
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mm->mmu_notifier_mm = LIST_POISON1; /* debug */
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}
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/*
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* This releases the mm_count pin automatically and frees the mm
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* structure if it was the last user of it. It serializes against
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* running mmu notifiers with SRCU and against mmu_notifier_unregister
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* with the unregister lock + SRCU. All sptes must be dropped before
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* calling mmu_notifier_unregister. ->release or any other notifier
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* method may be invoked concurrently with mmu_notifier_unregister,
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* and only after mmu_notifier_unregister returned we're guaranteed
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* that ->release or any other method can't run anymore.
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*/
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void mmu_notifier_unregister(struct mmu_notifier *mn, struct mm_struct *mm)
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{
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BUG_ON(atomic_read(&mm->mm_count) <= 0);
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if (!hlist_unhashed(&mn->hlist)) {
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/*
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* SRCU here will force exit_mmap to wait for ->release to
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* finish before freeing the pages.
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*/
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int id;
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id = srcu_read_lock(&srcu);
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/*
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* exit_mmap will block in mmu_notifier_release to guarantee
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* that ->release is called before freeing the pages.
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*/
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if (mn->ops->release)
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mn->ops->release(mn, mm);
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srcu_read_unlock(&srcu, id);
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spin_lock(&mm->mmu_notifier_mm->lock);
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/*
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* Can not use list_del_rcu() since __mmu_notifier_release
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* can delete it before we hold the lock.
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*/
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hlist_del_init_rcu(&mn->hlist);
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spin_unlock(&mm->mmu_notifier_mm->lock);
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}
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/*
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* Wait for any running method to finish, of course including
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* ->release if it was run by mmu_notifier_release instead of us.
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*/
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synchronize_srcu(&srcu);
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BUG_ON(atomic_read(&mm->mm_count) <= 0);
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mmdrop(mm);
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}
|
|
EXPORT_SYMBOL_GPL(mmu_notifier_unregister);
|
|
|
|
static void mmu_notifier_free_rcu(struct rcu_head *rcu)
|
|
{
|
|
struct mmu_notifier *mn = container_of(rcu, struct mmu_notifier, rcu);
|
|
struct mm_struct *mm = mn->mm;
|
|
|
|
mn->ops->free_notifier(mn);
|
|
/* Pairs with the get in __mmu_notifier_register() */
|
|
mmdrop(mm);
|
|
}
|
|
|
|
/**
|
|
* mmu_notifier_put - Release the reference on the notifier
|
|
* @mn: The notifier to act on
|
|
*
|
|
* This function must be paired with each mmu_notifier_get(), it releases the
|
|
* reference obtained by the get. If this is the last reference then process
|
|
* to free the notifier will be run asynchronously.
|
|
*
|
|
* Unlike mmu_notifier_unregister() the get/put flow only calls ops->release
|
|
* when the mm_struct is destroyed. Instead free_notifier is always called to
|
|
* release any resources held by the user.
|
|
*
|
|
* As ops->release is not guaranteed to be called, the user must ensure that
|
|
* all sptes are dropped, and no new sptes can be established before
|
|
* mmu_notifier_put() is called.
|
|
*
|
|
* This function can be called from the ops->release callback, however the
|
|
* caller must still ensure it is called pairwise with mmu_notifier_get().
|
|
*
|
|
* Modules calling this function must call mmu_notifier_synchronize() in
|
|
* their __exit functions to ensure the async work is completed.
|
|
*/
|
|
void mmu_notifier_put(struct mmu_notifier *mn)
|
|
{
|
|
struct mm_struct *mm = mn->mm;
|
|
|
|
spin_lock(&mm->mmu_notifier_mm->lock);
|
|
if (WARN_ON(!mn->users) || --mn->users)
|
|
goto out_unlock;
|
|
hlist_del_init_rcu(&mn->hlist);
|
|
spin_unlock(&mm->mmu_notifier_mm->lock);
|
|
|
|
call_srcu(&srcu, &mn->rcu, mmu_notifier_free_rcu);
|
|
return;
|
|
|
|
out_unlock:
|
|
spin_unlock(&mm->mmu_notifier_mm->lock);
|
|
}
|
|
EXPORT_SYMBOL_GPL(mmu_notifier_put);
|
|
|
|
/**
|
|
* mmu_notifier_synchronize - Ensure all mmu_notifiers are freed
|
|
*
|
|
* This function ensures that all outstanding async SRU work from
|
|
* mmu_notifier_put() is completed. After it returns any mmu_notifier_ops
|
|
* associated with an unused mmu_notifier will no longer be called.
|
|
*
|
|
* Before using the caller must ensure that all of its mmu_notifiers have been
|
|
* fully released via mmu_notifier_put().
|
|
*
|
|
* Modules using the mmu_notifier_put() API should call this in their __exit
|
|
* function to avoid module unloading races.
|
|
*/
|
|
void mmu_notifier_synchronize(void)
|
|
{
|
|
synchronize_srcu(&srcu);
|
|
}
|
|
EXPORT_SYMBOL_GPL(mmu_notifier_synchronize);
|
|
|
|
bool
|
|
mmu_notifier_range_update_to_read_only(const struct mmu_notifier_range *range)
|
|
{
|
|
if (!range->vma || range->event != MMU_NOTIFY_PROTECTION_VMA)
|
|
return false;
|
|
/* Return true if the vma still have the read flag set. */
|
|
return range->vma->vm_flags & VM_READ;
|
|
}
|
|
EXPORT_SYMBOL_GPL(mmu_notifier_range_update_to_read_only);
|