[PATCH v2 06/11] mm/hmm: improve driver API to work and wait over a range v2

jglisse
2019-03-25T14:40:58Z

From: Jérôme Glisse <jglisse@redhat.com>

A common use case for HMM mirror is user trying to mirror a range
and before they could program the hardware it get invalidated by
some core mm event. Instead of having user re-try right away to
mirror the range provide a completion mechanism for them to wait
for any active invalidation affecting the range.

This also changes how hmm_range_snapshot() and hmm_range_fault()
works by not relying on vma so that we can drop the mmap_sem
when waiting and lookup the vma again on retry.

Changes since v1:
- squashed: Dan Carpenter: potential deadlock in nonblocking code

Signed-off-by: Jérôme Glisse <jglisse@redhat.com>
Reviewed-by: Ralph Campbell <rcampbell@nvidia.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Matthew Wilcox <willy@infradead.org>
---
include/linux/hmm.h | 208 ++++++++++++++---
mm/hmm.c | 528 +++++++++++++++++++++-----------------------
2 files changed, 428 insertions(+), 308 deletions(-)

diff --git a/include/linux/hmm.h b/include/linux/hmm.h
index e9afd23c2eac..79671036cb5f 100644
--- a/include/linux/hmm.h
+++ b/include/linux/hmm.h
@@ -77,8 +77,34 @@
#include <linux/migrate.h>
#include <linux/memremap.h>
#include <linux/completion.h>
+#include <linux/mmu_notifier.h>

-struct hmm;
+
+/*
+ * struct hmm - HMM per mm struct
+ *
+ * @mm: mm struct this HMM struct is bound to
+ * @lock: lock protecting ranges list
+ * @ranges: list of range being snapshotted
+ * @mirrors: list of mirrors for this mm
+ * @mmu_notifier: mmu notifier to track updates to CPU page table
+ * @mirrors_sem: read/write semaphore protecting the mirrors list
+ * @wq: wait queue for user waiting on a range invalidation
+ * @notifiers: count of active mmu notifiers
+ * @dead: is the mm dead ?
+ */
+struct hmm {
+ struct mm_struct *mm;
+ struct kref kref;
+ struct mutex lock;
+ struct list_head ranges;
+ struct list_head mirrors;
+ struct mmu_notifier mmu_notifier;
+ struct rw_semaphore mirrors_sem;
+ wait_queue_head_t wq;
+ long notifiers;
+ bool dead;
+};

/*
* hmm_pfn_flag_e - HMM flag enums
@@ -155,6 +181,38 @@ struct hmm_range {
bool valid;
};

+/*
+ * hmm_range_wait_until_valid() - wait for range to be valid
+ * @range: range affected by invalidation to wait on
+ * @timeout: time out for wait in ms (ie abort wait after that period of time)
+ * Returns: true if the range is valid, false otherwise.
+ */
+static inline bool hmm_range_wait_until_valid(struct hmm_range *range,
+ unsigned long timeout)
+{
+ /* Check if mm is dead ? */
+ if (range->hmm == NULL || range->hmm->dead || range->hmm->mm == NULL) {
+ range->valid = false;
+ return false;
+ }
+ if (range->valid)
+ return true;
+ wait_event_timeout(range->hmm->wq, range->valid || range->hmm->dead,
+ msecs_to_jiffies(timeout));
+ /* Return current valid status just in case we get lucky */
+ return range->valid;
+}
+
+/*
+ * hmm_range_valid() - test if a range is valid or not
+ * @range: range
+ * Returns: true if the range is valid, false otherwise.
+ */
+static inline bool hmm_range_valid(struct hmm_range *range)
+{
+ return range->valid;
+}
+
/*
* hmm_pfn_to_page() - return struct page pointed to by a valid HMM pfn
* @range: range use to decode HMM pfn value
@@ -357,51 +415,133 @@ void hmm_mirror_unregister(struct hmm_mirror *mirror);

/*
- * To snapshot the CPU page table, call hmm_vma_get_pfns(), then take a device
- * driver lock that serializes device page table updates, then call
- * hmm_vma_range_done(), to check if the snapshot is still valid. The same
- * device driver page table update lock must also be used in the
- * hmm_mirror_ops.sync_cpu_device_pagetables() callback, so that CPU page
- * table invalidation serializes on it.
+ * To snapshot the CPU page table you first have to call hmm_range_register()
+ * to register the range. If hmm_range_register() return an error then some-
+ * thing is horribly wrong and you should fail loudly. If it returned true then
+ * you can wait for the range to be stable with hmm_range_wait_until_valid()
+ * function, a range is valid when there are no concurrent changes to the CPU
+ * page table for the range.
+ *
+ * Once the range is valid you can call hmm_range_snapshot() if that returns
+ * without error then you can take your device page table lock (the same lock
+ * you use in the HMM mirror sync_cpu_device_pagetables() callback). After
+ * taking that lock you have to check the range validity, if it is still valid
+ * (ie hmm_range_valid() returns true) then you can program the device page
+ * table, otherwise you have to start again. Pseudo code:
+ *
+ * mydevice_prefault(mydevice, mm, start, end)
+ * {
+ * struct hmm_range range;
+ * ...
*
- * YOU MUST CALL hmm_vma_range_done() ONCE AND ONLY ONCE EACH TIME YOU CALL
- * hmm_range_snapshot() WITHOUT ERROR !
+ * ret = hmm_range_register(&range, mm, start, end);
+ * if (ret)
+ * return ret;
*
- * IF YOU DO NOT FOLLOW THE ABOVE RULE THE SNAPSHOT CONTENT MIGHT BE INVALID !
- */
-long hmm_range_snapshot(struct hmm_range *range);
-bool hmm_vma_range_done(struct hmm_range *range);
-
-
-/*
- * Fault memory on behalf of device driver. Unlike handle_mm_fault(), this will
- * not migrate any device memory back to system memory. The HMM pfn array will
- * be updated with the fault result and current snapshot of the CPU page table
- * for the range.
+ * down_read(mm->mmap_sem);
+ * again:
+ *
+ * if (!hmm_range_wait_until_valid(&range, TIMEOUT)) {
+ * up_read(&mm->mmap_sem);
+ * hmm_range_unregister(range);
+ * // Handle time out, either sleep or retry or something else
+ * ...
+ * return -ESOMETHING; || goto again;
+ * }
+ *
+ * ret = hmm_range_snapshot(&range); or hmm_range_fault(&range);
+ * if (ret == -EAGAIN) {
+ * down_read(mm->mmap_sem);
+ * goto again;
+ * } else if (ret == -EBUSY) {
+ * goto again;
+ * }
+ *
+ * up_read(&mm->mmap_sem);
+ * if (ret) {
+ * hmm_range_unregister(range);
+ * return ret;
+ * }
+ *
+ * // It might not have snap-shoted the whole range but only the first
+ * // npages, the return values is the number of valid pages from the
+ * // start of the range.
+ * npages = ret;
*
- * The mmap_sem must be taken in read mode before entering and it might be
- * dropped by the function if the block argument is false. In that case, the
- * function returns -EAGAIN.
+ * ...
*
- * Return value does not reflect if the fault was successful for every single
- * address or not. Therefore, the caller must to inspect the HMM pfn array to
- * determine fault status for each address.
+ * mydevice_page_table_lock(mydevice);
+ * if (!hmm_range_valid(range)) {
+ * mydevice_page_table_unlock(mydevice);
+ * goto again;
+ * }
*
- * Trying to fault inside an invalid vma will result in -EINVAL.
+ * mydevice_populate_page_table(mydevice, range, npages);
+ * ...
+ * mydevice_take_page_table_unlock(mydevice);
+ * hmm_range_unregister(range);
*
- * See the function description in mm/hmm.c for further documentation.
+ * return 0;
+ * }
+ *
+ * The same scheme apply to hmm_range_fault() (ie replace hmm_range_snapshot()
+ * with hmm_range_fault() in above pseudo code).
+ *
+ * YOU MUST CALL hmm_range_unregister() ONCE AND ONLY ONCE EACH TIME YOU CALL
+ * hmm_range_register() AND hmm_range_register() RETURNED TRUE ! IF YOU DO NOT
+ * FOLLOW THIS RULE MEMORY CORRUPTION WILL ENSUE !
*/
+int hmm_range_register(struct hmm_range *range,
+ struct mm_struct *mm,
+ unsigned long start,
+ unsigned long end);
+void hmm_range_unregister(struct hmm_range *range);
+long hmm_range_snapshot(struct hmm_range *range);
long hmm_range_fault(struct hmm_range *range, bool block);

+/*
+ * HMM_RANGE_DEFAULT_TIMEOUT - default timeout (ms) when waiting for a range
+ *
+ * When waiting for mmu notifiers we need some kind of time out otherwise we
+ * could potentialy wait for ever, 1000ms ie 1s sounds like a long time to
+ * wait already.
+ */
+#define HMM_RANGE_DEFAULT_TIMEOUT 1000
+
/* This is a temporary helper to avoid merge conflict between trees. */
+static inline bool hmm_vma_range_done(struct hmm_range *range)
+{
+ bool ret = hmm_range_valid(range);
+
+ hmm_range_unregister(range);
+ return ret;
+}
+
static inline int hmm_vma_fault(struct hmm_range *range, bool block)
{
- long ret = hmm_range_fault(range, block);
- if (ret == -EBUSY)
- ret = -EAGAIN;
- else if (ret == -EAGAIN)
- ret = -EBUSY;
- return ret < 0 ? ret : 0;
+ long ret;
+
+ ret = hmm_range_register(range, range->vma->vm_mm,
+ range->start, range->end);
+ if (ret)
+ return (int)ret;
+
+ if (!hmm_range_wait_until_valid(range, HMM_RANGE_DEFAULT_TIMEOUT)) {
+ up_read(&range->vma->vm_mm->mmap_sem);
+ return -EAGAIN;
+ }
+
+ ret = hmm_range_fault(range, block);
+ if (ret <= 0) {
+ if (ret == -EBUSY || !ret) {
+ up_read(&range->vma->vm_mm->mmap_sem);
+ ret = -EBUSY;
+ } else if (ret == -EAGAIN)
+ ret = -EBUSY;
+ hmm_range_unregister(range);
+ return ret;
+ }
+ return 0;
}

/* Below are for HMM internal use only! Not to be used by device driver! */
diff --git a/mm/hmm.c b/mm/hmm.c
index 7860e63c3ba7..fa9498eeb9b6 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -38,26 +38,6 @@
#if IS_ENABLED(CONFIG_HMM_MIRROR)
static const struct mmu_notifier_ops hmm_mmu_notifier_ops;

-/*
- * struct hmm - HMM per mm struct
- *
- * @mm: mm struct this HMM struct is bound to
- * @lock: lock protecting ranges list
- * @ranges: list of range being snapshotted
- * @mirrors: list of mirrors for this mm
- * @mmu_notifier: mmu notifier to track updates to CPU page table
- * @mirrors_sem: read/write semaphore protecting the mirrors list
- */
-struct hmm {
- struct mm_struct *mm;
- struct kref kref;
- spinlock_t lock;
- struct list_head ranges;
- struct list_head mirrors;
- struct mmu_notifier mmu_notifier;
- struct rw_semaphore mirrors_sem;
-};
-
static inline struct hmm *mm_get_hmm(struct mm_struct *mm)
{
struct hmm *hmm = READ_ONCE(mm->hmm);
@@ -87,12 +67,15 @@ static struct hmm *hmm_register(struct mm_struct *mm)
hmm = kmalloc(sizeof(*hmm), GFP_KERNEL);
if (!hmm)
return NULL;
+ init_waitqueue_head(&hmm->wq);
INIT_LIST_HEAD(&hmm->mirrors);
init_rwsem(&hmm->mirrors_sem);
hmm->mmu_notifier.ops = NULL;
INIT_LIST_HEAD(&hmm->ranges);
- spin_lock_init(&hmm->lock);
+ mutex_init(&hmm->lock);
kref_init(&hmm->kref);
+ hmm->notifiers = 0;
+ hmm->dead = false;
hmm->mm = mm;

spin_lock(&mm->page_table_lock);
@@ -154,6 +137,7 @@ void hmm_mm_destroy(struct mm_struct *mm)
mm->hmm = NULL;
if (hmm) {
hmm->mm = NULL;
+ hmm->dead = true;
spin_unlock(&mm->page_table_lock);
hmm_put(hmm);
return;
@@ -162,43 +146,22 @@ void hmm_mm_destroy(struct mm_struct *mm)
spin_unlock(&mm->page_table_lock);
}

-static int hmm_invalidate_range(struct hmm *hmm, bool device,
- const struct hmm_update *update)
+static void hmm_release(struct mmu_notifier *mn, struct mm_struct *mm)
{
+ struct hmm *hmm = mm_get_hmm(mm);
struct hmm_mirror *mirror;
struct hmm_range *range;

- spin_lock(&hmm->lock);
- list_for_each_entry(range, &hmm->ranges, list) {
- if (update->end < range->start || update->start >= range->end)
- continue;
+ /* Report this HMM as dying. */
+ hmm->dead = true;

+ /* Wake-up everyone waiting on any range. */
+ mutex_lock(&hmm->lock);
+ list_for_each_entry(range, &hmm->ranges, list) {
range->valid = false;
}
- spin_unlock(&hmm->lock);
-
- if (!device)
- return 0;
-
- down_read(&hmm->mirrors_sem);
- list_for_each_entry(mirror, &hmm->mirrors, list) {
- int ret;
-
- ret = mirror->ops->sync_cpu_device_pagetables(mirror, update);
- if (!update->blockable && ret == -EAGAIN) {
- up_read(&hmm->mirrors_sem);
- return -EAGAIN;
- }
- }
- up_read(&hmm->mirrors_sem);
-
- return 0;
-}
-
-static void hmm_release(struct mmu_notifier *mn, struct mm_struct *mm)
-{
- struct hmm_mirror *mirror;
- struct hmm *hmm = mm_get_hmm(mm);
+ wake_up_all(&hmm->wq);
+ mutex_unlock(&hmm->lock);

down_write(&hmm->mirrors_sem);
mirror = list_first_entry_or_null(&hmm->mirrors, struct hmm_mirror,
@@ -224,36 +187,80 @@ static void hmm_release(struct mmu_notifier *mn, struct mm_struct *mm)
}

static int hmm_invalidate_range_start(struct mmu_notifier *mn,
- const struct mmu_notifier_range *range)
+ const struct mmu_notifier_range *nrange)
{
- struct hmm *hmm = mm_get_hmm(range->mm);
+ struct hmm *hmm = mm_get_hmm(nrange->mm);
+ struct hmm_mirror *mirror;
struct hmm_update update;
- int ret;
+ struct hmm_range *range;
+ int ret = 0;

VM_BUG_ON(!hmm);

- update.start = range->start;
- update.end = range->end;
+ update.start = nrange->start;
+ update.end = nrange->end;
update.event = HMM_UPDATE_INVALIDATE;
- update.blockable = range->blockable;
- ret = hmm_invalidate_range(hmm, true, &update);
+ update.blockable = nrange->blockable;
+
+ if (nrange->blockable)
+ mutex_lock(&hmm->lock);
+ else if (!mutex_trylock(&hmm->lock)) {
+ ret = -EAGAIN;
+ goto out;
+ }
+ hmm->notifiers++;
+ list_for_each_entry(range, &hmm->ranges, list) {
+ if (update.end < range->start || update.start >= range->end)
+ continue;
+
+ range->valid = false;
+ }
+ mutex_unlock(&hmm->lock);
+
+ if (nrange->blockable)
+ down_read(&hmm->mirrors_sem);
+ else if (!down_read_trylock(&hmm->mirrors_sem)) {
+ ret = -EAGAIN;
+ goto out;
+ }
+ list_for_each_entry(mirror, &hmm->mirrors, list) {
+ int ret;
+
+ ret = mirror->ops->sync_cpu_device_pagetables(mirror, &update);
+ if (!update.blockable && ret == -EAGAIN) {
+ up_read(&hmm->mirrors_sem);
+ ret = -EAGAIN;
+ goto out;
+ }
+ }
+ up_read(&hmm->mirrors_sem);
+
+out:
hmm_put(hmm);
return ret;
}

static void hmm_invalidate_range_end(struct mmu_notifier *mn,
- const struct mmu_notifier_range *range)
+ const struct mmu_notifier_range *nrange)
{
- struct hmm *hmm = mm_get_hmm(range->mm);
- struct hmm_update update;
+ struct hmm *hmm = mm_get_hmm(nrange->mm);

VM_BUG_ON(!hmm);

- update.start = range->start;
- update.end = range->end;
- update.event = HMM_UPDATE_INVALIDATE;
- update.blockable = true;
- hmm_invalidate_range(hmm, false, &update);
+ mutex_lock(&hmm->lock);
+ hmm->notifiers--;
+ if (!hmm->notifiers) {
+ struct hmm_range *range;
+
+ list_for_each_entry(range, &hmm->ranges, list) {
+ if (range->valid)
+ continue;
+ range->valid = true;
+ }
+ wake_up_all(&hmm->wq);
+ }
+ mutex_unlock(&hmm->lock);
+
hmm_put(hmm);
}

@@ -405,7 +412,6 @@ static inline void hmm_pte_need_fault(const struct hmm_vma_walk *hmm_vma_walk,
{
struct hmm_range *range = hmm_vma_walk->range;

- *fault = *write_fault = false;
if (!hmm_vma_walk->fault)
return;

@@ -444,10 +450,11 @@ static void hmm_range_need_fault(const struct hmm_vma_walk *hmm_vma_walk,
return;
}

+ *fault = *write_fault = false;
for (i = 0; i < npages; ++i) {
hmm_pte_need_fault(hmm_vma_walk, pfns[i], cpu_flags,
fault, write_fault);
- if ((*fault) || (*write_fault))
+ if ((*write_fault))
return;
}
}
@@ -702,162 +709,152 @@ static void hmm_pfns_special(struct hmm_range *range)
}

/*
- * hmm_range_snapshot() - snapshot CPU page table for a range
+ * hmm_range_register() - start tracking change to CPU page table over a range
* @range: range
- * Returns: number of valid pages in range->pfns[] (from range start
- * address). This may be zero. If the return value is negative,
- * then one of the following values may be returned:
+ * @mm: the mm struct for the range of virtual address
+ * @start: start virtual address (inclusive)
+ * @end: end virtual address (exclusive)
+ * Returns 0 on success, -EFAULT if the address space is no longer valid
*
- * -EINVAL invalid arguments or mm or virtual address are in an
- * invalid vma (ie either hugetlbfs or device file vma).
- * -EPERM For example, asking for write, when the range is
- * read-only
- * -EAGAIN Caller needs to retry
- * -EFAULT Either no valid vma exists for this range, or it is
- * illegal to access the range
- *
- * This snapshots the CPU page table for a range of virtual addresses. Snapshot
- * validity is tracked by range struct. See hmm_vma_range_done() for further
- * information.
+ * Track updates to the CPU page table see include/linux/hmm.h
*/
-long hmm_range_snapshot(struct hmm_range *range)
+int hmm_range_register(struct hmm_range *range,
+ struct mm_struct *mm,
+ unsigned long start,
+ unsigned long end)
{
- struct vm_area_struct *vma = range->vma;
- struct hmm_vma_walk hmm_vma_walk;
- struct mm_walk mm_walk;
- struct hmm *hmm;
-
+ range->start = start & PAGE_MASK;
+ range->end = end & PAGE_MASK;
+ range->valid = false;
range->hmm = NULL;

- /* Sanity check, this really should not happen ! */
- if (range->start < vma->vm_start || range->start >= vma->vm_end)
- return -EINVAL;
- if (range->end < vma->vm_start || range->end > vma->vm_end)
+ if (range->start >= range->end)
return -EINVAL;

- hmm = hmm_register(vma->vm_mm);
- if (!hmm)
- return -ENOMEM;
+ range->hmm = hmm_register(mm);
+ if (!range->hmm)
+ return -EFAULT;

/* Check if hmm_mm_destroy() was call. */
- if (hmm->mm == NULL) {
- hmm_put(hmm);
- return -EINVAL;
+ if (range->hmm->mm == NULL || range->hmm->dead) {
+ hmm_put(range->hmm);
+ return -EFAULT;
}

- /* FIXME support hugetlb fs */
- if (is_vm_hugetlb_page(vma) || (vma->vm_flags & VM_SPECIAL) ||
- vma_is_dax(vma)) {
- hmm_pfns_special(range);
- hmm_put(hmm);
- return -EINVAL;
- }
+ /* Initialize range to track CPU page table update */
+ mutex_lock(&range->hmm->lock);

- if (!(vma->vm_flags & VM_READ)) {
- /*
- * If vma do not allow read access, then assume that it does
- * not allow write access, either. Architecture that allow
- * write without read access are not supported by HMM, because
- * operations such has atomic access would not work.
- */
- hmm_pfns_clear(range, range->pfns, range->start, range->end);
- hmm_put(hmm);
- return -EPERM;
- }
+ list_add_rcu(&range->list, &range->hmm->ranges);

- /* Initialize range to track CPU page table update */
- spin_lock(&hmm->lock);
- range->valid = true;
- list_add_rcu(&range->list, &hmm->ranges);
- spin_unlock(&hmm->lock);
-
- hmm_vma_walk.fault = false;
- hmm_vma_walk.range = range;
- mm_walk.private = &hmm_vma_walk;
- hmm_vma_walk.last = range->start;
-
- mm_walk.vma = vma;
- mm_walk.mm = vma->vm_mm;
- mm_walk.pte_entry = NULL;
- mm_walk.test_walk = NULL;
- mm_walk.hugetlb_entry = NULL;
- mm_walk.pmd_entry = hmm_vma_walk_pmd;
- mm_walk.pte_hole = hmm_vma_walk_hole;
-
- walk_page_range(range->start, range->end, &mm_walk);
/*
- * Transfer hmm reference to the range struct it will be drop inside
- * the hmm_vma_range_done() function (which _must_ be call if this
- * function return 0).
+ * If there are any concurrent notifiers we have to wait for them for
+ * the range to be valid (see hmm_range_wait_until_valid()).
*/
- range->hmm = hmm;
- return (hmm_vma_walk.last - range->start) >> PAGE_SHIFT;
+ if (!range->hmm->notifiers)
+ range->valid = true;
+ mutex_unlock(&range->hmm->lock);
+
+ return 0;
}
-EXPORT_SYMBOL(hmm_range_snapshot);
+EXPORT_SYMBOL(hmm_range_register);

/*
- * hmm_vma_range_done() - stop tracking change to CPU page table over a range
- * @range: range being tracked
- * Returns: false if range data has been invalidated, true otherwise
+ * hmm_range_unregister() - stop tracking change to CPU page table over a range
+ * @range: range
*
* Range struct is used to track updates to the CPU page table after a call to
- * either hmm_vma_get_pfns() or hmm_vma_fault(). Once the device driver is done
- * using the data, or wants to lock updates to the data it got from those
- * functions, it must call the hmm_vma_range_done() function, which will then
- * stop tracking CPU page table updates.
- *
- * Note that device driver must still implement general CPU page table update
- * tracking either by using hmm_mirror (see hmm_mirror_register()) or by using
- * the mmu_notifier API directly.
- *
- * CPU page table update tracking done through hmm_range is only temporary and
- * to be used while trying to duplicate CPU page table contents for a range of
- * virtual addresses.
- *
- * There are two ways to use this :
- * again:
- * hmm_vma_get_pfns(range); or hmm_vma_fault(...);
- * trans = device_build_page_table_update_transaction(pfns);
- * device_page_table_lock();
- * if (!hmm_vma_range_done(range)) {
- * device_page_table_unlock();
- * goto again;
- * }
- * device_commit_transaction(trans);
- * device_page_table_unlock();
- *
- * Or:
- * hmm_vma_get_pfns(range); or hmm_vma_fault(...);
- * device_page_table_lock();
- * hmm_vma_range_done(range);
- * device_update_page_table(range->pfns);
- * device_page_table_unlock();
+ * hmm_range_register(). See include/linux/hmm.h for how to use it.
*/
-bool hmm_vma_range_done(struct hmm_range *range)
+void hmm_range_unregister(struct hmm_range *range)
{
- bool ret = false;
-
/* Sanity check this really should not happen. */
- if (range->hmm == NULL || range->end <= range->start) {
- BUG();
- return false;
- }
+ if (range->hmm == NULL || range->end <= range->start)
+ return;

- spin_lock(&range->hmm->lock);
+ mutex_lock(&range->hmm->lock);
list_del_rcu(&range->list);
- ret = range->valid;
- spin_unlock(&range->hmm->lock);
-
- /* Is the mm still alive ? */
- if (range->hmm->mm == NULL)
- ret = false;
+ mutex_unlock(&range->hmm->lock);

- /* Drop reference taken by hmm_vma_fault() or hmm_vma_get_pfns() */
+ /* Drop reference taken by hmm_range_register() */
+ range->valid = false;
hmm_put(range->hmm);
range->hmm = NULL;
- return ret;
}
-EXPORT_SYMBOL(hmm_vma_range_done);
+EXPORT_SYMBOL(hmm_range_unregister);
+
+/*
+ * hmm_range_snapshot() - snapshot CPU page table for a range
+ * @range: range
+ * Returns: -EINVAL if invalid argument, -ENOMEM out of memory, -EPERM invalid
+ * permission (for instance asking for write and range is read only),
+ * -EAGAIN if you need to retry, -EFAULT invalid (ie either no valid
+ * vma or it is illegal to access that range), number of valid pages
+ * in range->pfns[] (from range start address).
+ *
+ * This snapshots the CPU page table for a range of virtual addresses. Snapshot
+ * validity is tracked by range struct. See in include/linux/hmm.h for example
+ * on how to use.
+ */
+long hmm_range_snapshot(struct hmm_range *range)
+{
+ unsigned long start = range->start, end;
+ struct hmm_vma_walk hmm_vma_walk;
+ struct hmm *hmm = range->hmm;
+ struct vm_area_struct *vma;
+ struct mm_walk mm_walk;
+
+ /* Check if hmm_mm_destroy() was call. */
+ if (hmm->mm == NULL || hmm->dead)
+ return -EFAULT;
+
+ do {
+ /* If range is no longer valid force retry. */
+ if (!range->valid)
+ return -EAGAIN;
+
+ vma = find_vma(hmm->mm, start);
+ if (vma == NULL || (vma->vm_flags & VM_SPECIAL))
+ return -EFAULT;
+
+ /* FIXME support hugetlb fs/dax */
+ if (is_vm_hugetlb_page(vma) || vma_is_dax(vma)) {
+ hmm_pfns_special(range);
+ return -EINVAL;
+ }
+
+ if (!(vma->vm_flags & VM_READ)) {
+ /*
+ * If vma do not allow read access, then assume that it
+ * does not allow write access, either. HMM does not
+ * support architecture that allow write without read.
+ */
+ hmm_pfns_clear(range, range->pfns,
+ range->start, range->end);
+ return -EPERM;
+ }
+
+ range->vma = vma;
+ hmm_vma_walk.last = start;
+ hmm_vma_walk.fault = false;
+ hmm_vma_walk.range = range;
+ mm_walk.private = &hmm_vma_walk;
+ end = min(range->end, vma->vm_end);
+
+ mm_walk.vma = vma;
+ mm_walk.mm = vma->vm_mm;
+ mm_walk.pte_entry = NULL;
+ mm_walk.test_walk = NULL;
+ mm_walk.hugetlb_entry = NULL;
+ mm_walk.pmd_entry = hmm_vma_walk_pmd;
+ mm_walk.pte_hole = hmm_vma_walk_hole;
+
+ walk_page_range(start, end, &mm_walk);
+ start = end;
+ } while (start < range->end);
+
+ return (hmm_vma_walk.last - range->start) >> PAGE_SHIFT;
+}
+EXPORT_SYMBOL(hmm_range_snapshot);

/*
* hmm_range_fault() - try to fault some address in a virtual address range
@@ -889,96 +886,79 @@ EXPORT_SYMBOL(hmm_vma_range_done);
*/
long hmm_range_fault(struct hmm_range *range, bool block)
{
- struct vm_area_struct *vma = range->vma;
- unsigned long start = range->start;
+ unsigned long start = range->start, end;
struct hmm_vma_walk hmm_vma_walk;
+ struct hmm *hmm = range->hmm;
+ struct vm_area_struct *vma;
struct mm_walk mm_walk;
- struct hmm *hmm;
int ret;

- range->hmm = NULL;
-
- /* Sanity check, this really should not happen ! */
- if (range->start < vma->vm_start || range->start >= vma->vm_end)
- return -EINVAL;
- if (range->end < vma->vm_start || range->end > vma->vm_end)
- return -EINVAL;
+ /* Check if hmm_mm_destroy() was call. */
+ if (hmm->mm == NULL || hmm->dead)
+ return -EFAULT;

- hmm = hmm_register(vma->vm_mm);
- if (!hmm) {
- hmm_pfns_clear(range, range->pfns, range->start, range->end);
- return -ENOMEM;
- }
+ do {
+ /* If range is no longer valid force retry. */
+ if (!range->valid) {
+ up_read(&hmm->mm->mmap_sem);
+ return -EAGAIN;
+ }

- /* Check if hmm_mm_destroy() was call. */
- if (hmm->mm == NULL) {
- hmm_put(hmm);
- return -EINVAL;
- }
+ vma = find_vma(hmm->mm, start);
+ if (vma == NULL || (vma->vm_flags & VM_SPECIAL))
+ return -EFAULT;

- /* FIXME support hugetlb fs */
- if (is_vm_hugetlb_page(vma) || (vma->vm_flags & VM_SPECIAL) ||
- vma_is_dax(vma)) {
- hmm_pfns_special(range);
- hmm_put(hmm);
- return -EINVAL;
- }
+ /* FIXME support hugetlb fs/dax */
+ if (is_vm_hugetlb_page(vma) || vma_is_dax(vma)) {
+ hmm_pfns_special(range);
+ return -EINVAL;
+ }

- if (!(vma->vm_flags & VM_READ)) {
- /*
- * If vma do not allow read access, then assume that it does
- * not allow write access, either. Architecture that allow
- * write without read access are not supported by HMM, because
- * operations such has atomic access would not work.
- */
- hmm_pfns_clear(range, range->pfns, range->start, range->end);
- hmm_put(hmm);
- return -EPERM;
- }
+ if (!(vma->vm_flags & VM_READ)) {
+ /*
+ * If vma do not allow read access, then assume that it
+ * does not allow write access, either. HMM does not
+ * support architecture that allow write without read.
+ */
+ hmm_pfns_clear(range, range->pfns,
+ range->start, range->end);
+ return -EPERM;
+ }

- /* Initialize range to track CPU page table update */
- spin_lock(&hmm->lock);
- range->valid = true;
- list_add_rcu(&range->list, &hmm->ranges);
- spin_unlock(&hmm->lock);
-
- hmm_vma_walk.fault = true;
- hmm_vma_walk.block = block;
- hmm_vma_walk.range = range;
- mm_walk.private = &hmm_vma_walk;
- hmm_vma_walk.last = range->start;
-
- mm_walk.vma = vma;
- mm_walk.mm = vma->vm_mm;
- mm_walk.pte_entry = NULL;
- mm_walk.test_walk = NULL;
- mm_walk.hugetlb_entry = NULL;
- mm_walk.pmd_entry = hmm_vma_walk_pmd;
- mm_walk.pte_hole = hmm_vma_walk_hole;
+ range->vma = vma;
+ hmm_vma_walk.last = start;
+ hmm_vma_walk.fault = true;
+ hmm_vma_walk.block = block;
+ hmm_vma_walk.range = range;
+ mm_walk.private = &hmm_vma_walk;
+ end = min(range->end, vma->vm_end);
+
+ mm_walk.vma = vma;
+ mm_walk.mm = vma->vm_mm;
+ mm_walk.pte_entry = NULL;
+ mm_walk.test_walk = NULL;
+ mm_walk.hugetlb_entry = NULL;
+ mm_walk.pmd_entry = hmm_vma_walk_pmd;
+ mm_walk.pte_hole = hmm_vma_walk_hole;
+
+ do {
+ ret = walk_page_range(start, end, &mm_walk);
+ start = hmm_vma_walk.last;
+
+ /* Keep trying while the range is valid. */
+ } while (ret == -EBUSY && range->valid);
+
+ if (ret) {
+ unsigned long i;
+
+ i = (hmm_vma_walk.last - range->start) >> PAGE_SHIFT;
+ hmm_pfns_clear(range, &range->pfns[i],
+ hmm_vma_walk.last, range->end);
+ return ret;
+ }
+ start = end;

- do {
- ret = walk_page_range(start, range->end, &mm_walk);
- start = hmm_vma_walk.last;
- /* Keep trying while the range is valid. */
- } while (ret == -EBUSY && range->valid);
-
- if (ret) {
- unsigned long i;
-
- i = (hmm_vma_walk.last - range->start) >> PAGE_SHIFT;
- hmm_pfns_clear(range, &range->pfns[i], hmm_vma_walk.last,
- range->end);
- hmm_vma_range_done(range);
- hmm_put(hmm);
- return ret;
- } else {
- /*
- * Transfer hmm reference to the range struct it will be drop
- * inside the hmm_vma_range_done() function (which _must_ be
- * call if this function return 0).
- */
- range->hmm = hmm;
- }
+ } while (start < range->end);

return (hmm_vma_walk.last - range->start) >> PAGE_SHIFT;
}
--
2.17.2