On 01/12/2015 05:46 PM, Jerome Glisse wrote:
> On Sun, Jan 11, 2015 at 03:24:42PM +0200, Oded Gabbay wrote:
>>
>>
>> On 01/06/2015 12:44 AM, j.glisse@xxxxxxxxx wrote:
>>> From: Jérôme Glisse <jglisse@xxxxxxxxxx>
>>>
>>> This patch only introduce core HMM functions for registering a new mirror and
>>> stopping a mirror as well as registering and unregistering a device.
>>>
>>> The lifecycle of HMM object is handled differently then one of mmu_notifier
>>> because unlike mmu_notifier there can be concurrent call from both mm code to
>>> HMM code and/or from device driver code to HMM code. Moreover lifetime of HMM
>>> can be uncorrelated from the lifetime of the process that is being mirror.
>>>
>>> Changed since v1:
>>> - Updated comment of hmm_device_register().
>>>
>>> Signed-off-by: Jérôme Glisse <jglisse@xxxxxxxxxx>
>>> Signed-off-by: Sherry Cheung <SCheung@xxxxxxxxxx>
>>> Signed-off-by: Subhash Gutti <sgutti@xxxxxxxxxx>
>>> Signed-off-by: Mark Hairgrove <mhairgrove@xxxxxxxxxx>
>>> Signed-off-by: John Hubbard <jhubbard@xxxxxxxxxx>
>>> Signed-off-by: Jatin Kumar <jakumar@xxxxxxxxxx>
>>> ---
>>> MAINTAINERS | 7 +
>>> include/linux/hmm.h | 129 ++++++++++++++++
>>> include/linux/mm.h | 11 ++
>>> include/linux/mm_types.h | 14 ++
>>> kernel/fork.c | 2 +
>>> mm/Kconfig | 15 ++
>>> mm/Makefile | 1 +
>>> mm/hmm.c | 373 +++++++++++++++++++++++++++++++++++++++++++++++
>>> 8 files changed, 552 insertions(+)
>>> create mode 100644 include/linux/hmm.h
>>> create mode 100644 mm/hmm.c
>>>
>>> diff --git a/MAINTAINERS b/MAINTAINERS
>>> index c03bc6c..3ec87c4 100644
>>> --- a/MAINTAINERS
>>> +++ b/MAINTAINERS
>>> @@ -4533,6 +4533,13 @@ F: include/uapi/linux/if_hippi.h
>>> F: net/802/hippi.c
>>> F: drivers/net/hippi/
>>>
>>> +HMM - Heterogeneous Memory Management
>>> +M: Jérôme Glisse <jglisse@xxxxxxxxxx>
>>> +L: linux-mm@xxxxxxxxx
>>> +S: Maintained
>>> +F: mm/hmm.c
>>> +F: include/linux/hmm.h
>>> +
>>> HOST AP DRIVER
>>> M: Jouni Malinen <j@xxxxx>
>>> L: hostap@xxxxxxxxx (subscribers-only)
>>> diff --git a/include/linux/hmm.h b/include/linux/hmm.h
>>> new file mode 100644
>>> index 0000000..8eddc15
>>> --- /dev/null
>>> +++ b/include/linux/hmm.h
>>> @@ -0,0 +1,129 @@
>>> +/*
>>> + * Copyright 2013 Red Hat Inc.
>>> + *
>>> + * This program is free software; you can redistribute it and/or modify
>>> + * it under the terms of the GNU General Public License as published by
>>> + * the Free Software Foundation; either version 2 of the License, or
>>> + * (at your option) any later version.
>>> + *
>>> + * This program is distributed in the hope that it will be useful,
>>> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
>>> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
>>> + * GNU General Public License for more details.
>>> + *
>>> + * Authors: Jérôme Glisse <jglisse@xxxxxxxxxx>
>>> + */
>>> +/* This is a heterogeneous memory management (hmm). In a nutshell this provide
>>> + * an API to mirror a process address on a device which has its own mmu using
>>> + * its own page table for the process. It supports everything except special
>>> + * vma.
>>> + *
>>> + * Mandatory hardware features :
>>> + * - An mmu with pagetable.
>>> + * - Read only flag per cpu page.
>>> + * - Page fault ie hardware must stop and wait for kernel to service fault.
>>> + *
>>> + * Optional hardware features :
>>> + * - Dirty bit per cpu page.
>>> + * - Access bit per cpu page.
>>> + *
>>> + * The hmm code handle all the interfacing with the core kernel mm code and
>>> + * provide a simple API. It does support migrating system memory to device
>>> + * memory and handle migration back to system memory on cpu page fault.
>>> + *
>>> + * Migrated memory is considered as swaped from cpu and core mm code point of
>>> + * view.
>>> + */
>>> +#ifndef _HMM_H
>>> +#define _HMM_H
>>> +
>>> +#ifdef CONFIG_HMM
>>> +
>>> +#include <linux/list.h>
>>> +#include <linux/spinlock.h>
>>> +#include <linux/atomic.h>
>>> +#include <linux/mm_types.h>
>>> +#include <linux/mmu_notifier.h>
>>> +#include <linux/workqueue.h>
>>> +#include <linux/mman.h>
>>> +
>>> +
>>> +struct hmm_device;
>>> +struct hmm_mirror;
>>> +struct hmm;
>>> +
>>> +
>>> +/* hmm_device - Each device must register one and only one hmm_device.
>>> + *
>>> + * The hmm_device is the link btw HMM and each device driver.
>>> + */
>>> +
>>> +/* struct hmm_device_operations - HMM device operation callback
>>> + */
>>> +struct hmm_device_ops {
>>> + /* release() - mirror must stop using the address space.
>>> + *
>>> + * @mirror: The mirror that link process address space with the device.
>>> + *
>>> + * This callback is call either on mm destruction or as result to a
>>> + * call to hmm_mirror_release(). Device driver have to stop all hw
>>> + * thread and all usage of the address space, it has to dirty all pages
>>> + * that have been dirty by the device. But it must not clear any entry
>>> + * from the mirror page table.
>>> + */
>>> + void (*release)(struct hmm_mirror *mirror);
>>> +};
>>> +
>>> +/* struct hmm_device - per device HMM structure
>>> + *
>>> + * @name: Device name (uniquely identify the device on the system).
>>> + * @ops: The hmm operations callback.
>>> + * @mirrors: List of all active mirrors for the device.
>>> + * @mutex: Mutex protecting mirrors list.
>>> + *
>>> + * Each device that want to mirror an address space must register one of this
>>> + * struct (only once per linux device).
>>> + */
>>> +struct hmm_device {
>>> + const char *name;
>>> + const struct hmm_device_ops *ops;
>>> + struct list_head mirrors;
>>> + struct mutex mutex;
>>> +};
>>> +
>>> +int hmm_device_register(struct hmm_device *device);
>>> +int hmm_device_unregister(struct hmm_device *device);
>>> +
>>> +
>>> +/* hmm_mirror - device specific mirroring functions.
>>> + *
>>> + * Each device that mirror a process has a uniq hmm_mirror struct associating
>>> + * the process address space with the device. Same process can be mirrored by
>>> + * several different devices at the same time.
>>> + */
>>> +
>>> +/* struct hmm_mirror - per device and per mm HMM structure
>>> + *
>>> + * @device: The hmm_device struct this hmm_mirror is associated to.
>>> + * @hmm: The hmm struct this hmm_mirror is associated to.
>>> + * @dlist: List of all hmm_mirror for same device.
>>> + * @mlist: List of all hmm_mirror for same process.
>>> + *
>>> + * Each device that want to mirror an address space must register one of this
>>> + * struct for each of the address space it wants to mirror. Same device can
>>> + * mirror several different address space. As well same address space can be
>>> + * mirror by different devices.
>>> + */
>>> +struct hmm_mirror {
>>> + struct hmm_device *device;
>>> + struct hmm *hmm;
>>> + struct list_head dlist;
>>> + struct hlist_node mlist;
>>> +};
>>> +
>>> +int hmm_mirror_register(struct hmm_mirror *mirror, struct hmm_device *device);
>>> +void hmm_mirror_unregister(struct hmm_mirror *mirror);
>>> +
>>> +
>>> +#endif /* CONFIG_HMM */
>>> +#endif
>>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>>> index f80d019..0e054f9 100644
>>> --- a/include/linux/mm.h
>>> +++ b/include/linux/mm.h
>>> @@ -2208,5 +2208,16 @@ void __init setup_nr_node_ids(void);
>>> static inline void setup_nr_node_ids(void) {}
>>> #endif
>>>
>>> +#ifdef CONFIG_HMM
>>> +static inline void hmm_mm_init(struct mm_struct *mm)
>>> +{
>>> + mm->hmm = NULL;
>>> +}
>>> +#else /* !CONFIG_HMM */
>>> +static inline void hmm_mm_init(struct mm_struct *mm)
>>> +{
>>> +}
>>> +#endif /* !CONFIG_HMM */
>>> +
>>> #endif /* __KERNEL__ */
>>> #endif /* _LINUX_MM_H */
>>> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
>>> index 6d34aa2..57a3e1c 100644
>>> --- a/include/linux/mm_types.h
>>> +++ b/include/linux/mm_types.h
>>> @@ -15,6 +15,10 @@
>>> #include <asm/page.h>
>>> #include <asm/mmu.h>
>>>
>>> +#ifdef CONFIG_HMM
>>> +struct hmm;
>>> +#endif
>>> +
>>> #ifndef AT_VECTOR_SIZE_ARCH
>>> #define AT_VECTOR_SIZE_ARCH 0
>>> #endif
>>> @@ -426,6 +430,16 @@ struct mm_struct {
>>> #ifdef CONFIG_MMU_NOTIFIER
>>> struct mmu_notifier_mm *mmu_notifier_mm;
>>> #endif
>>> +#ifdef CONFIG_HMM
>>> + /*
>>> + * hmm always register an mmu_notifier we rely on mmu notifier to keep
>>> + * refcount on mm struct as well as forbiding registering hmm on a
>>> + * dying mm
>>> + *
>>> + * This field is set with mmap_sem old in write mode.
>>> + */
>>> + struct hmm *hmm;
>>> +#endif
>>> #if defined(CONFIG_TRANSPARENT_HUGEPAGE) && !USE_SPLIT_PMD_PTLOCKS
>>> pgtable_t pmd_huge_pte; /* protected by page_table_lock */
>>> #endif
>>> diff --git a/kernel/fork.c b/kernel/fork.c
>>> index 4dc2dda..0bb9dc4 100644
>>> --- a/kernel/fork.c
>>> +++ b/kernel/fork.c
>>> @@ -27,6 +27,7 @@
>>> #include <linux/binfmts.h>
>>> #include <linux/mman.h>
>>> #include <linux/mmu_notifier.h>
>>> +#include <linux/hmm.h>
>>> #include <linux/fs.h>
>>> #include <linux/mm.h>
>>> #include <linux/vmacache.h>
>>> @@ -568,6 +569,7 @@ static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p)
>>> mm_init_aio(mm);
>>> mm_init_owner(mm, p);
>>> mmu_notifier_mm_init(mm);
>>> + hmm_mm_init(mm);
>>> clear_tlb_flush_pending(mm);
>>> #if defined(CONFIG_TRANSPARENT_HUGEPAGE) && !USE_SPLIT_PMD_PTLOCKS
>>> mm->pmd_huge_pte = NULL;
>>> diff --git a/mm/Kconfig b/mm/Kconfig
>>> index 1d1ae6b..b249db0 100644
>>> --- a/mm/Kconfig
>>> +++ b/mm/Kconfig
>>> @@ -618,3 +618,18 @@ config MAX_STACK_SIZE_MB
>>> changed to a smaller value in which case that is used.
>>>
>>> A sane initial value is 80 MB.
>>> +
>>> +if STAGING
>>> +config HMM
>>> + bool "Enable heterogeneous memory management (HMM)"
>>> + depends on MMU
>>> + select MMU_NOTIFIER
>>> + select GENERIC_PAGE_TABLE
>>> + default n
>>> + help
>>> + Heterogeneous memory management provide infrastructure for a device
>>> + to mirror a process address space into an hardware mmu or into any
>>> + things supporting pagefault like event.
>>> +
>>> + If unsure, say N to disable hmm.
>>> +endif # STAGING
>>> diff --git a/mm/Makefile b/mm/Makefile
>>> index 3548460..cb2f9ed 100644
>>> --- a/mm/Makefile
>>> +++ b/mm/Makefile
>>> @@ -73,3 +73,4 @@ obj-$(CONFIG_GENERIC_EARLY_IOREMAP) += early_ioremap.o
>>> obj-$(CONFIG_CMA) += cma.o
>>> obj-$(CONFIG_MEMORY_BALLOON) += balloon_compaction.o
>>> obj-$(CONFIG_PAGE_EXTENSION) += page_ext.o
>>> +obj-$(CONFIG_HMM) += hmm.o
>>> diff --git a/mm/hmm.c b/mm/hmm.c
>>> new file mode 100644
>>> index 0000000..0b4e220
>>> --- /dev/null
>>> +++ b/mm/hmm.c
>>> @@ -0,0 +1,373 @@
>>> +/*
>>> + * Copyright 2013 Red Hat Inc.
>>> + *
>>> + * This program is free software; you can redistribute it and/or modify
>>> + * it under the terms of the GNU General Public License as published by
>>> + * the Free Software Foundation; either version 2 of the License, or
>>> + * (at your option) any later version.
>>> + *
>>> + * This program is distributed in the hope that it will be useful,
>>> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
>>> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
>>> + * GNU General Public License for more details.
>>> + *
>>> + * Authors: Jérôme Glisse <jglisse@xxxxxxxxxx>
>>> + */
>>> +/* This is the core code for heterogeneous memory management (HMM). HMM intend
>>> + * to provide helper for mirroring a process address space on a device as well
>>> + * as allowing migration of data between system memory and device memory refer
>>> + * as remote memory from here on out.
>>> + *
>>> + * Refer to include/linux/hmm.h for further information on general design.
>>> + */
>>> +#include <linux/export.h>
>>> +#include <linux/bitmap.h>
>>> +#include <linux/list.h>
>>> +#include <linux/rculist.h>
>>> +#include <linux/slab.h>
>>> +#include <linux/mmu_notifier.h>
>>> +#include <linux/mm.h>
>>> +#include <linux/hugetlb.h>
>>> +#include <linux/fs.h>
>>> +#include <linux/file.h>
>>> +#include <linux/ksm.h>
>>> +#include <linux/rmap.h>
>>> +#include <linux/swap.h>
>>> +#include <linux/swapops.h>
>>> +#include <linux/mmu_context.h>
>>> +#include <linux/memcontrol.h>
>>> +#include <linux/hmm.h>
>>> +#include <linux/wait.h>
>>> +#include <linux/mman.h>
>>> +#include <linux/delay.h>
>>> +#include <linux/workqueue.h>
>>> +
>>> +#include "internal.h"
>>> +
>>> +static struct srcu_struct srcu;
>>> +
>>> +
>>> +/* struct hmm - per mm_struct HMM states.
>>> + *
>>> + * @mirrors: List of all mirror for this mm (one per device).
>>> + * @mm: The mm struct this hmm is associated with.
>>> + * @vm_end: Last valid address for this mm (exclusive).
>>> + * @lock: Serialize the mirror list modifications.
>>> + * @kref: Reference counter
>>> + * @mmu_notifier: The mmu_notifier of this mm.
>>> + *
>>> + * For each process address space (mm_struct) there is one and only one hmm
>>> + * struct. hmm functions will redispatch to each devices the change made to
>>> + * the process address space.
>>> + */
>>> +struct hmm {
>>> + struct hlist_head mirrors;
>>> + struct mm_struct *mm;
>>> + unsigned long vm_end;
>>> + spinlock_t lock;
>>> + struct kref kref;
>>> + struct mmu_notifier mmu_notifier;
>>> +};
>>> +
>>> +static struct mmu_notifier_ops hmm_notifier_ops;
>>> +
>>> +
>>> +/* hmm - core HMM functions.
>>> + *
>>> + * Core HMM functions that deal with all the process mm activities.
>>> + */
>>> +
>>> +static int hmm_init(struct hmm *hmm)
>>> +{
>>> + hmm->mm = current->mm;
>>> + hmm->vm_end = TASK_SIZE;
>>> + kref_init(&hmm->kref);
>>> + INIT_HLIST_HEAD(&hmm->mirrors);
>>> + spin_lock_init(&hmm->lock);
>>> +
>>> + /* register notifier */
>>> + hmm->mmu_notifier.ops = &hmm_notifier_ops;
>>> + return __mmu_notifier_register(&hmm->mmu_notifier, current->mm);
>>> +}
>>> +
>>> +static int hmm_add_mirror(struct hmm *hmm, struct hmm_mirror *mirror)
>>> +{
>>> + struct hmm_mirror *tmp;
>>> +
>>> + spin_lock(&hmm->lock);
>>> + hlist_for_each_entry_rcu(tmp, &hmm->mirrors, mlist)
>>> + if (tmp->device == mirror->device) {
>>> + /* Same device can mirror only once. */
>>> + spin_unlock(&hmm->lock);
>>> + return -EINVAL;
>>> + }
>>> + hlist_add_head(&mirror->mlist, &hmm->mirrors);
>>> + spin_unlock(&hmm->lock);
>>> +
>>> + return 0;
>>> +}
>>> +
>>> +static inline struct hmm *hmm_ref(struct hmm *hmm)
>>> +{
>>> + if (!hmm || !kref_get_unless_zero(&hmm->kref))
>>> + return NULL;
>>> + return hmm;
>>> +}
>>> +
>>> +static void hmm_destroy(struct kref *kref)
>>> +{
>>> + struct hmm *hmm;
>>> +
>>> + hmm = container_of(kref, struct hmm, kref);
>>> + BUG_ON(!hlist_empty(&hmm->mirrors));
>>> +
>>> + down_write(&hmm->mm->mmap_sem);
>>> + /* A new hmm might have been register before reaching that point. */
>>> + if (hmm->mm->hmm == hmm)
>>> + hmm->mm->hmm = NULL;
>>> + up_write(&hmm->mm->mmap_sem);
>>> +
>>> + mmu_notifier_unregister(&hmm->mmu_notifier, hmm->mm);
>>> +
>>> + kfree(hmm);
>> Jerome,
>> Don't you need to handle a case where the process is terminated before it
>> calls hmm_mirror_unregister() ? or if it "forgets" to call that function in
>> the first place ?
>>
>> This is the only place I saw "kfree(hmm)" and this function is only called
>> if there are no more references to hmm. I saw you unref only in
>> hmm_mirror_unregister() but as I said, that function may never be called.
>>
>> Oded
>
> It's a design decision, ie the driver will get a callback if the process is kill
> and it then become driver responsability to call hmm_mirror_unregister(). As in
> most case the driver will already be cleaning up, this sounded like cleaniest
> way.
>
Yeah, I see that now. Thanks for the explanation.
Oded
>
>>
>>> +}
>>> +
>>> +static inline struct hmm *hmm_unref(struct hmm *hmm)
>>> +{
>>> + if (hmm)
>>> + kref_put(&hmm->kref, hmm_destroy);
>>> + return NULL;
>>> +}
>>> +
>>> +
>>> +/* hmm_notifier - HMM callback for mmu_notifier tracking change to process mm.
>>> + *
>>> + * HMM use use mmu notifier to track change made to process address space.
>>> + */
>>> +static void hmm_notifier_release(struct mmu_notifier *mn, struct mm_struct *mm)
>>> +{
>>> + struct hmm *hmm;
>>> + int id;
>>> +
>>> + /*
>>> + * The hmm structure can not be free because the mmu_notifier srcu is
>>> + * read locked thus any concurrent hmm_mirror_unregister that would
>>> + * free hmm would have to wait on the mmu_notifier srcu.
>>> + */
>>> + hmm = container_of(mn, struct hmm, mmu_notifier);
>>> +
>>> + id = srcu_read_lock(&srcu);
>>> + spin_lock(&hmm->lock);
>>> + while (hmm->mirrors.first) {
>>> + struct hmm_mirror *mirror;
>>> +
>>> + mirror = hlist_entry(hmm->mirrors.first,
>>> + struct hmm_mirror,
>>> + mlist);
>>> + hlist_del_init_rcu(&mirror->mlist);
>>> + spin_unlock(&hmm->lock);
>>> +
>>> + mirror->device->ops->release(mirror);
>>> +
>>> + mutex_lock(&mirror->device->mutex);
>>> + list_del_init(&mirror->dlist);
>>> + mutex_unlock(&mirror->device->mutex);
>>> +
>>> + spin_lock(&hmm->lock);
>>> + }
>>> + spin_unlock(&hmm->lock);
>>> +
>>> + srcu_read_unlock(&srcu, id);
>>> +}
>>> +
>>> +static struct mmu_notifier_ops hmm_notifier_ops = {
>>> + .release = hmm_notifier_release,
>>> +};
>>> +
>>> +
>>> +/* hmm_mirror - per device mirroring functions.
>>> + *
>>> + * Each device that mirror a process has a uniq hmm_mirror struct. A process
>>> + * can be mirror by several devices at the same time.
>>> + *
>>> + * Below are all the functions and their helpers use by device driver to mirror
>>> + * the process address space. Those functions either deals with updating the
>>> + * device page table (through hmm callback). Or provide helper functions use by
>>> + * the device driver to fault in range of memory in the device page table.
>>> + */
>>> +
>>> +/* hmm_mirror_register() - register mirror against current process for a device.
>>> + *
>>> + * @mirror: The mirror struct being registered.
>>> + * @device: The device struct to against which the mirror is registered.
>>> + * Returns: 0 on success or -ENOMEM, -EINVAL on error.
>>> + *
>>> + * Call when device driver want to start mirroring a process address space. The
>>> + * HMM shim will register mmu_notifier and start monitoring process address
>>> + * space changes. Hence callback to device driver might happen even before this
>>> + * function return.
>>> + *
>>> + * The task device driver want to mirror must be current !
>>> + *
>>> + * Only one mirror per mm and hmm_device can be created, it will return NULL if
>>> + * the hmm_device already has an hmm_mirror for the the mm.
>>> + */
>>> +int hmm_mirror_register(struct hmm_mirror *mirror, struct hmm_device *device)
>>> +{
>>> + struct mm_struct *mm = current->mm;
>>> + struct hmm *hmm = NULL;
>>> + int ret = 0;
>>> +
>>> + /* Sanity checks. */
>>> + BUG_ON(!device);
>>> + BUG_ON(!mm);
>>> +
>>> + /*
>>> + * Initialize the mirror struct fields, the mlist init and del dance is
>>> + * necessary to make the error path easier for driver and for hmm.
>>> + */
>>> + INIT_HLIST_NODE(&mirror->mlist);
>>> + INIT_LIST_HEAD(&mirror->dlist);
>>> + mutex_lock(&device->mutex);
>>> + mirror->device = device;
>>> + list_add(&mirror->dlist, &device->mirrors);
>>> + mutex_unlock(&device->mutex);
>>> +
>>> + down_write(&mm->mmap_sem);
>>> +
>>> + hmm = mm->hmm ? hmm_ref(hmm) : NULL;
>>> + if (hmm == NULL) {
>>> + /* no hmm registered yet so register one */
>>> + hmm = kzalloc(sizeof(*mm->hmm), GFP_KERNEL);
>>> + if (hmm == NULL) {
>>> + up_write(&mm->mmap_sem);
>>> + ret = -ENOMEM;
>>> + goto error;
>>> + }
>>> +
>>> + ret = hmm_init(hmm);
>>> + if (ret) {
>>> + up_write(&mm->mmap_sem);
>>> + kfree(hmm);
>>> + goto error;
>>> + }
>>> +
>>> + mm->hmm = hmm;
>>> + }
>>> +
>>> + mirror->hmm = hmm;
>>> + ret = hmm_add_mirror(hmm, mirror);
>>> + up_write(&mm->mmap_sem);
>>> + if (ret) {
>>> + mirror->hmm = NULL;
>>> + hmm_unref(hmm);
>>> + goto error;
>>> + }
>>> + return 0;
>>> +
>>> +error:
>>> + mutex_lock(&device->mutex);
>>> + list_del_init(&mirror->dlist);
>>> + mutex_unlock(&device->mutex);
>>> + return ret;
>>> +}
>>> +EXPORT_SYMBOL(hmm_mirror_register);
>>> +
>>> +static void hmm_mirror_release(struct hmm_mirror *mirror)
>>> +{
>>> + spin_lock(&mirror->hmm->lock);
>>> + if (!hlist_unhashed(&mirror->mlist)) {
>>> + hlist_del_init_rcu(&mirror->mlist);
>>> + spin_unlock(&mirror->hmm->lock);
>>> + mirror->device->ops->release(mirror);
>>> +
>>> + mutex_lock(&mirror->device->mutex);
>>> + list_del_init(&mirror->dlist);
>>> + mutex_unlock(&mirror->device->mutex);
>>> + } else
>>> + spin_unlock(&mirror->hmm->lock);
>>> +}
>>> +
>>> +/* hmm_mirror_unregister() - unregister a mirror.
>>> + *
>>> + * @mirror: The mirror that link process address space with the device.
>>> + *
>>> + * Driver can call this function when it wants to stop mirroring a process.
>>> + * This will trigger a call to the ->stop() callback if it did not aleady
>>> + * happen.
>>> + */
>>> +void hmm_mirror_unregister(struct hmm_mirror *mirror)
>>> +{
>>> + int id;
>>> +
>>> + id = srcu_read_lock(&srcu);
>>> + hmm_mirror_release(mirror);
>>> + srcu_read_unlock(&srcu, id);
>>> +
>>> + /*
>>> + * Wait for any running method to finish, of course including
>>> + * ->release() if it was run by hmm_notifier_release instead of us.
>>> + */
>>> + synchronize_srcu(&srcu);
>>> +
>>> + mirror->hmm = hmm_unref(mirror->hmm);
>>> +}
>>> +EXPORT_SYMBOL(hmm_mirror_unregister);
>>> +
>>> +
>>> +/* hmm_device - Each device driver must register one and only one hmm_device
>>> + *
>>> + * The hmm_device is the link btw HMM and each device driver.
>>> + */
>>> +
>>> +/* hmm_device_register() - register a device with HMM.
>>> + *
>>> + * @device: The hmm_device struct.
>>> + * Returns: 0 on success or -EINVAL otherwise.
>>> + *
>>> + *
>>> + * Call when device driver want to register itself with HMM. Device driver must
>>> + * only register once.
>>> + */
>>> +int hmm_device_register(struct hmm_device *device)
>>> +{
>>> + /* sanity check */
>>> + BUG_ON(!device);
>>> + BUG_ON(!device->name);
>>> + BUG_ON(!device->ops);
>>> + BUG_ON(!device->ops->release);
>>> +
>>> + mutex_init(&device->mutex);
>>> + INIT_LIST_HEAD(&device->mirrors);
>>> +
>>> + return 0;
>>> +}
>>> +EXPORT_SYMBOL(hmm_device_register);
>>> +
>>> +/* hmm_device_unregister() - unregister a device with HMM.
>>> + *
>>> + * @device: The hmm_device struct.
>>> + * Returns: 0 on success or -EBUSY otherwise.
>>> + *
>>> + * Call when device driver want to unregister itself with HMM. This will check
>>> + * that there is no any active mirror and returns -EBUSY if so.
>>> + */
>>> +int hmm_device_unregister(struct hmm_device *device)
>>> +{
>>> + mutex_lock(&device->mutex);
>>> + if (!list_empty(&device->mirrors)) {
>>> + mutex_unlock(&device->mutex);
>>> + return -EBUSY;
>>> + }
>>> + mutex_unlock(&device->mutex);
>>> + synchronize_srcu(&srcu);
>>> + return 0;
>>> +}
>>> +EXPORT_SYMBOL(hmm_device_unregister);
>>> +
>>> +
>>> +static int __init hmm_subsys_init(void)
>>> +{
>>> + return init_srcu_struct(&srcu);
>>> +}
>>> +subsys_initcall(hmm_subsys_init);
>>>
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