[v10,23/25] mm/gup: track FOLL_PIN pages
diff mbox series

Message ID 20191212081917.1264184-24-jhubbard@nvidia.com
State New
Headers show
Series
  • mm/gup: track dma-pinned pages: FOLL_PIN
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Commit Message

John Hubbard Dec. 12, 2019, 8:19 a.m. UTC
Add tracking of pages that were pinned via FOLL_PIN.

As mentioned in the FOLL_PIN documentation, callers who effectively set
FOLL_PIN are required to ultimately free such pages via unpin_user_page().
The effect is similar to FOLL_GET, and may be thought of as "FOLL_GET
for DIO and/or RDMA use".

Pages that have been pinned via FOLL_PIN are identifiable via a
new function call:

   bool page_dma_pinned(struct page *page);

What to do in response to encountering such a page, is left to later
patchsets. There is discussion about this in [1], [2], and [3].

This also changes a BUG_ON(), to a WARN_ON(), in follow_page_mask().

[1] Some slow progress on get_user_pages() (Apr 2, 2019):
    https://lwn.net/Articles/784574/
[2] DMA and get_user_pages() (LPC: Dec 12, 2018):
    https://lwn.net/Articles/774411/
[3] The trouble with get_user_pages() (Apr 30, 2018):
    https://lwn.net/Articles/753027/

Suggested-by: Jan Kara <jack@suse.cz>
Suggested-by: Jérôme Glisse <jglisse@redhat.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 Documentation/core-api/pin_user_pages.rst |   2 +-
 include/linux/mm.h                        |  77 ++++-
 include/linux/mmzone.h                    |   2 +
 include/linux/page_ref.h                  |  10 +
 mm/gup.c                                  | 399 +++++++++++++++++-----
 mm/huge_memory.c                          |  45 ++-
 mm/hugetlb.c                              |  38 ++-
 mm/vmstat.c                               |   2 +
 8 files changed, 436 insertions(+), 139 deletions(-)

Comments

Jan Kara Dec. 12, 2019, 10:17 a.m. UTC | #1
On Thu 12-12-19 00:19:15, John Hubbard wrote:
> Add tracking of pages that were pinned via FOLL_PIN.
> 
> As mentioned in the FOLL_PIN documentation, callers who effectively set
> FOLL_PIN are required to ultimately free such pages via unpin_user_page().
> The effect is similar to FOLL_GET, and may be thought of as "FOLL_GET
> for DIO and/or RDMA use".
> 
> Pages that have been pinned via FOLL_PIN are identifiable via a
> new function call:
> 
>    bool page_dma_pinned(struct page *page);
> 
> What to do in response to encountering such a page, is left to later
> patchsets. There is discussion about this in [1], [2], and [3].
> 
> This also changes a BUG_ON(), to a WARN_ON(), in follow_page_mask().
> 
> [1] Some slow progress on get_user_pages() (Apr 2, 2019):
>     https://lwn.net/Articles/784574/
> [2] DMA and get_user_pages() (LPC: Dec 12, 2018):
>     https://lwn.net/Articles/774411/
> [3] The trouble with get_user_pages() (Apr 30, 2018):
>     https://lwn.net/Articles/753027/
> 
> Suggested-by: Jan Kara <jack@suse.cz>
> Suggested-by: Jérôme Glisse <jglisse@redhat.com>
> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>

Thanks for the patch. As a side note, given this series is rather big, it
may be better to send just individual updated patches (as replies to the
review comments) instead of resending the whole series every time. And then
you can resend the whole series once enough changes accumulate or we reach
seemingly final state.  That way people don't have to crawl through lots of
uninteresing emails...  Just something to keep in mind for the future.

I've spotted just one issue in this patch (see below), the rest are just
small style nits.

> +#define page_ref_zero_or_close_to_bias_overflow(page) \
> +	((unsigned int) page_ref_count(page) + \
> +		GUP_PIN_COUNTING_BIAS <= GUP_PIN_COUNTING_BIAS)
> +

...

> +/**
> + * page_dma_pinned() - report if a page is pinned for DMA.
> + *
> + * This function checks if a page has been pinned via a call to
> + * pin_user_pages*().
> + *
> + * The return value is partially fuzzy: false is not fuzzy, because it means
> + * "definitely not pinned for DMA", but true means "probably pinned for DMA, but
> + * possibly a false positive due to having at least GUP_PIN_COUNTING_BIAS worth
> + * of normal page references".
> + *
> + * False positives are OK, because: a) it's unlikely for a page to get that many
> + * refcounts, and b) all the callers of this routine are expected to be able to
> + * deal gracefully with a false positive.
> + *
> + * For more information, please see Documentation/vm/pin_user_pages.rst.
> + *
> + * @page:	pointer to page to be queried.
> + * @Return:	True, if it is likely that the page has been "dma-pinned".
> + *		False, if the page is definitely not dma-pinned.
> + */
> +static inline bool page_dma_pinned(struct page *page)
> +{
> +	return (page_ref_count(compound_head(page))) >= GUP_PIN_COUNTING_BIAS;
> +}
> +

I realized one think WRT handling of page refcount overflow: Page refcount is
signed and e.g. try_get_page() fails once the refcount is negative. That
means that:

a) page_ref_zero_or_close_to_bias_overflow() is not necessary - all places
that use pinning (i.e., advance refcount by GUP_PIN_COUNTING_BIAS) are not
necesary, we should just rely on the check for negative value for
consistency.

b) page_dma_pinned() has to be careful and type page_ref_count() to
unsigned type for comparison as otherwise overflowed refcount would
suddently appear as not-pinned.

> +/**
> + * try_pin_compound_head() - mark a compound page as being used by
> + * pin_user_pages*().
> + *
> + * This is the FOLL_PIN counterpart to try_get_compound_head().
> + *
> + * @page:	pointer to page to be marked
> + * @Return:	the compound head page, with ref appropriately incremented,
> + * or NULL upon failure.
> + */
> +__must_check struct page *try_pin_compound_head(struct page *page, int refs)
> +{
> +	struct page *head = try_get_compound_head(page,
> +						  GUP_PIN_COUNTING_BIAS * refs);
> +	if (!head)
> +		return NULL;
> +
> +	__update_proc_vmstat(page, NR_FOLL_PIN_REQUESTED, refs);
> +	return head;
> +}
> +
> +/*
> + * try_grab_compound_head() - attempt to elevate a page's refcount, by a
> + * flags-dependent amount.
> + *
> + * "grab" names in this file mean, "look at flags to decide whether to use
> + * FOLL_PIN or FOLL_GET behavior, when incrementing the page's refcount.
> + *
> + * Either FOLL_PIN or FOLL_GET (or neither) must be set, but not both at the
> + * same time. (That's true throughout the get_user_pages*() and
> + * pin_user_pages*() APIs.) Cases:
> + *
> + *	FOLL_GET: page's refcount will be incremented by 1.
> + *      FOLL_PIN: page's refcount will be incremented by GUP_PIN_COUNTING_BIAS.

Some tab vs space issue here... Generally we don't use tabs inside comments
for indenting so I'd wote for using just spaces.

> + *
> + * Return: head page (with refcount appropriately incremented) for success, or
> + * NULL upon failure. If neither FOLL_GET nor FOLL_PIN was set, that's
> + * considered failure, and furthermore, a likely bug in the caller, so a warning
> + * is also emitted.
> + */
> +static __maybe_unused struct page *try_grab_compound_head(struct page *page,
> +							  int refs,
> +							  unsigned int flags)
> +{
> +	if (flags & FOLL_GET)
> +		return try_get_compound_head(page, refs);
> +	else if (flags & FOLL_PIN)
> +		return try_pin_compound_head(page, refs);
> +
> +	WARN_ON_ONCE((flags & (FOLL_GET | FOLL_PIN)) == 0);

This could be just WARN_ON_ONCE(1), right?

> +	return NULL;
> +}
> +
> +/**
> + * try_grab_page() - elevate a page's refcount by a flag-dependent amount
> + *
> + * This might not do anything at all, depending on the flags argument.
> + *
> + * "grab" names in this file mean, "look at flags to decide whether to use
> + * FOLL_PIN or FOLL_GET behavior, when incrementing the page's refcount.
> + *
> + * @page:	pointer to page to be grabbed
> + * @flags:	gup flags: these are the FOLL_* flag values.
> + *
> + * Either FOLL_PIN or FOLL_GET (or neither) may be set, but not both at the same
> + * time. Cases:
> + *
> + *	FOLL_GET: page's refcount will be incremented by 1.
> + *      FOLL_PIN: page's refcount will be incremented by GUP_PIN_COUNTING_BIAS.

Again tab vs space difference here.

> + *
> + * Return: true for success, or if no action was required (if neither FOLL_PIN
> + * nor FOLL_GET was set, nothing is done). False for failure: FOLL_GET or
> + * FOLL_PIN was set, but the page could not be grabbed.
> + */
> +bool __must_check try_grab_page(struct page *page, unsigned int flags)
> +{
> +	if (flags & FOLL_GET)
> +		return try_get_page(page);
> +	else if (flags & FOLL_PIN) {
> +		page = compound_head(page);
> +		WARN_ON_ONCE(flags & FOLL_GET);
> +
> +		if (WARN_ON_ONCE(page_ref_zero_or_close_to_bias_overflow(page)))
> +			return false;

As I mentioned above, this will need "negative refcount" check instead...

> +
> +		page_ref_add(page, GUP_PIN_COUNTING_BIAS);
> +		__update_proc_vmstat(page, NR_FOLL_PIN_REQUESTED, 1);
> +	}
> +
> +	return true;
> +}

...

> @@ -1468,6 +1482,7 @@ struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
>  {
>  	struct mm_struct *mm = vma->vm_mm;
>  	struct page *page = NULL;
> +	struct page *subpage = NULL;
>  
>  	assert_spin_locked(pmd_lockptr(mm, pmd));
>  
> @@ -1486,6 +1501,14 @@ struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
>  	VM_BUG_ON_PAGE(!PageHead(page) && !is_zone_device_page(page), page);
>  	if (flags & FOLL_TOUCH)
>  		touch_pmd(vma, addr, pmd, flags);
> +
> +	subpage = page;
> +	subpage += (addr & ~HPAGE_PMD_MASK) >> PAGE_SHIFT;
> +	VM_BUG_ON_PAGE(!PageCompound(subpage) &&
> +		       !is_zone_device_page(subpage), subpage);
> +	if (!try_grab_page(subpage, flags))
> +		return ERR_PTR(-EFAULT);
> +

Hum, I think you've made this change more complex than it has to be.
try_grab_page() is the same for head page or subpage because we increment
the refcount on the compound_head(page) anyway. So I'd leave this function
as is (not add subpage or move VM_BUG_ON_PAGE()), just have at this place:

	if (!try_grab_page(page, flags))
		return ERR_PTR(-EFAULT);

Also one comment regarding the error code. Some places seem to return -ENOMEM
when they fail to grab page reference. Shouldn't we rather return that one
for consistency?

>  	if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) {
>  		/*
>  		 * We don't mlock() pte-mapped THPs. This way we can avoid
> @@ -1509,24 +1532,18 @@ struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
>  		 */
>  
>  		if (PageAnon(page) && compound_mapcount(page) != 1)
> -			goto skip_mlock;
> +			goto out;
>  		if (PageDoubleMap(page) || !page->mapping)
> -			goto skip_mlock;
> +			goto out;
>  		if (!trylock_page(page))
> -			goto skip_mlock;
> +			goto out;
>  		lru_add_drain();
>  		if (page->mapping && !PageDoubleMap(page))
>  			mlock_vma_page(page);
>  		unlock_page(page);
>  	}
> -skip_mlock:
> -	page += (addr & ~HPAGE_PMD_MASK) >> PAGE_SHIFT;
> -	VM_BUG_ON_PAGE(!PageCompound(page) && !is_zone_device_page(page), page);
> -	if (flags & FOLL_GET)
> -		get_page(page);
> -
>  out:
> -	return page;
> +	return subpage;
>  }
>  

									Honza

Patch
diff mbox series

diff --git a/Documentation/core-api/pin_user_pages.rst b/Documentation/core-api/pin_user_pages.rst
index 1d490155ecd7..2db14df1f2d7 100644
--- a/Documentation/core-api/pin_user_pages.rst
+++ b/Documentation/core-api/pin_user_pages.rst
@@ -53,7 +53,7 @@  Which flags are set by each wrapper
 For these pin_user_pages*() functions, FOLL_PIN is OR'd in with whatever gup
 flags the caller provides. The caller is required to pass in a non-null struct
 pages* array, and the function then pin pages by incrementing each by a special
-value. For now, that value is +1, just like get_user_pages*().::
+value: GUP_PIN_COUNTING_BIAS.::
 
  Function
  --------
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 6a1a357e7d86..1765332f27e8 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1005,6 +1005,10 @@  static inline bool is_pci_p2pdma_page(const struct page *page)
 #define page_ref_zero_or_close_to_overflow(page) \
 	((unsigned int) page_ref_count(page) + 127u <= 127u)
 
+#define page_ref_zero_or_close_to_bias_overflow(page) \
+	((unsigned int) page_ref_count(page) + \
+		GUP_PIN_COUNTING_BIAS <= GUP_PIN_COUNTING_BIAS)
+
 static inline void get_page(struct page *page)
 {
 	page = compound_head(page);
@@ -1016,6 +1020,8 @@  static inline void get_page(struct page *page)
 	page_ref_inc(page);
 }
 
+bool __must_check try_grab_page(struct page *page, unsigned int flags);
+
 static inline __must_check bool try_get_page(struct page *page)
 {
 	page = compound_head(page);
@@ -1044,29 +1050,70 @@  static inline void put_page(struct page *page)
 		__put_page(page);
 }
 
-/**
- * unpin_user_page() - release a gup-pinned page
- * @page:            pointer to page to be released
+/*
+ * GUP_PIN_COUNTING_BIAS, and the associated functions that use it, overload
+ * the page's refcount so that two separate items are tracked: the original page
+ * reference count, and also a new count of how many pin_user_pages() calls were
+ * made against the page. ("gup-pinned" is another term for the latter).
+ *
+ * With this scheme, pin_user_pages() becomes special: such pages are marked as
+ * distinct from normal pages. As such, the unpin_user_page() call (and its
+ * variants) must be used in order to release gup-pinned pages.
  *
- * Pages that were pinned via pin_user_pages*() must be released via either
- * unpin_user_page(), or one of the unpin_user_pages*() routines. This is so
- * that eventually such pages can be separately tracked and uniquely handled. In
- * particular, interactions with RDMA and filesystems need special handling.
+ * Choice of value:
  *
- * unpin_user_page() and put_page() are not interchangeable, despite this early
- * implementation that makes them look the same. unpin_user_page() calls must
- * be perfectly matched up with pin*() calls.
+ * By making GUP_PIN_COUNTING_BIAS a power of two, debugging of page reference
+ * counts with respect to pin_user_pages() and unpin_user_page() becomes
+ * simpler, due to the fact that adding an even power of two to the page
+ * refcount has the effect of using only the upper N bits, for the code that
+ * counts up using the bias value. This means that the lower bits are left for
+ * the exclusive use of the original code that increments and decrements by one
+ * (or at least, by much smaller values than the bias value).
+ *
+ * Of course, once the lower bits overflow into the upper bits (and this is
+ * OK, because subtraction recovers the original values), then visual inspection
+ * no longer suffices to directly view the separate counts. However, for normal
+ * applications that don't have huge page reference counts, this won't be an
+ * issue.
+ *
+ * Locking: the lockless algorithm described in page_cache_get_speculative()
+ * and page_cache_gup_pin_speculative() provides safe operation for
+ * get_user_pages and page_mkclean and other calls that race to set up page
+ * table entries.
  */
-static inline void unpin_user_page(struct page *page)
-{
-	put_page(page);
-}
+#define GUP_PIN_COUNTING_BIAS (1U << 10)
 
+void unpin_user_page(struct page *page);
 void unpin_user_pages_dirty_lock(struct page **pages, unsigned long npages,
 				 bool make_dirty);
-
 void unpin_user_pages(struct page **pages, unsigned long npages);
 
+/**
+ * page_dma_pinned() - report if a page is pinned for DMA.
+ *
+ * This function checks if a page has been pinned via a call to
+ * pin_user_pages*().
+ *
+ * The return value is partially fuzzy: false is not fuzzy, because it means
+ * "definitely not pinned for DMA", but true means "probably pinned for DMA, but
+ * possibly a false positive due to having at least GUP_PIN_COUNTING_BIAS worth
+ * of normal page references".
+ *
+ * False positives are OK, because: a) it's unlikely for a page to get that many
+ * refcounts, and b) all the callers of this routine are expected to be able to
+ * deal gracefully with a false positive.
+ *
+ * For more information, please see Documentation/vm/pin_user_pages.rst.
+ *
+ * @page:	pointer to page to be queried.
+ * @Return:	True, if it is likely that the page has been "dma-pinned".
+ *		False, if the page is definitely not dma-pinned.
+ */
+static inline bool page_dma_pinned(struct page *page)
+{
+	return (page_ref_count(compound_head(page))) >= GUP_PIN_COUNTING_BIAS;
+}
+
 #if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP)
 #define SECTION_IN_PAGE_FLAGS
 #endif
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 89d8ff06c9ce..a7418f7a44da 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -244,6 +244,8 @@  enum node_stat_item {
 	NR_DIRTIED,		/* page dirtyings since bootup */
 	NR_WRITTEN,		/* page writings since bootup */
 	NR_KERNEL_MISC_RECLAIMABLE,	/* reclaimable non-slab kernel pages */
+	NR_FOLL_PIN_REQUESTED,	/* via: pin_user_page(), gup flag: FOLL_PIN */
+	NR_FOLL_PIN_RETURNED,	/* pages returned via unpin_user_page() */
 	NR_VM_NODE_STAT_ITEMS
 };
 
diff --git a/include/linux/page_ref.h b/include/linux/page_ref.h
index 14d14beb1f7f..b9cbe553d1e7 100644
--- a/include/linux/page_ref.h
+++ b/include/linux/page_ref.h
@@ -102,6 +102,16 @@  static inline void page_ref_sub(struct page *page, int nr)
 		__page_ref_mod(page, -nr);
 }
 
+static inline int page_ref_sub_return(struct page *page, int nr)
+{
+	int ret = atomic_sub_return(nr, &page->_refcount);
+
+	if (page_ref_tracepoint_active(__tracepoint_page_ref_mod))
+		__page_ref_mod(page, -nr);
+
+	return ret;
+}
+
 static inline void page_ref_inc(struct page *page)
 {
 	atomic_inc(&page->_refcount);
diff --git a/mm/gup.c b/mm/gup.c
index 73aedcefa4bd..4da3ab274b10 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -36,6 +36,20 @@  static __always_inline long __gup_longterm_locked(struct task_struct *tsk,
 						  struct page **pages,
 						  struct vm_area_struct **vmas,
 						  unsigned int flags);
+
+#ifdef CONFIG_DEBUG_VM
+static inline void __update_proc_vmstat(struct page *page,
+					enum node_stat_item item, int count)
+{
+	mod_node_page_state(page_pgdat(page), item, count);
+}
+#else
+static inline void __update_proc_vmstat(struct page *page,
+					enum node_stat_item item, int count)
+{
+}
+#endif
+
 /*
  * Return the compound head page with ref appropriately incremented,
  * or NULL if that failed.
@@ -51,6 +65,156 @@  static inline struct page *try_get_compound_head(struct page *page, int refs)
 	return head;
 }
 
+/**
+ * try_pin_compound_head() - mark a compound page as being used by
+ * pin_user_pages*().
+ *
+ * This is the FOLL_PIN counterpart to try_get_compound_head().
+ *
+ * @page:	pointer to page to be marked
+ * @Return:	the compound head page, with ref appropriately incremented,
+ * or NULL upon failure.
+ */
+__must_check struct page *try_pin_compound_head(struct page *page, int refs)
+{
+	struct page *head = try_get_compound_head(page,
+						  GUP_PIN_COUNTING_BIAS * refs);
+	if (!head)
+		return NULL;
+
+	__update_proc_vmstat(page, NR_FOLL_PIN_REQUESTED, refs);
+	return head;
+}
+
+/*
+ * try_grab_compound_head() - attempt to elevate a page's refcount, by a
+ * flags-dependent amount.
+ *
+ * "grab" names in this file mean, "look at flags to decide whether to use
+ * FOLL_PIN or FOLL_GET behavior, when incrementing the page's refcount.
+ *
+ * Either FOLL_PIN or FOLL_GET (or neither) must be set, but not both at the
+ * same time. (That's true throughout the get_user_pages*() and
+ * pin_user_pages*() APIs.) Cases:
+ *
+ *	FOLL_GET: page's refcount will be incremented by 1.
+ *      FOLL_PIN: page's refcount will be incremented by GUP_PIN_COUNTING_BIAS.
+ *
+ * Return: head page (with refcount appropriately incremented) for success, or
+ * NULL upon failure. If neither FOLL_GET nor FOLL_PIN was set, that's
+ * considered failure, and furthermore, a likely bug in the caller, so a warning
+ * is also emitted.
+ */
+static __maybe_unused struct page *try_grab_compound_head(struct page *page,
+							  int refs,
+							  unsigned int flags)
+{
+	if (flags & FOLL_GET)
+		return try_get_compound_head(page, refs);
+	else if (flags & FOLL_PIN)
+		return try_pin_compound_head(page, refs);
+
+	WARN_ON_ONCE((flags & (FOLL_GET | FOLL_PIN)) == 0);
+	return NULL;
+}
+
+/**
+ * try_grab_page() - elevate a page's refcount by a flag-dependent amount
+ *
+ * This might not do anything at all, depending on the flags argument.
+ *
+ * "grab" names in this file mean, "look at flags to decide whether to use
+ * FOLL_PIN or FOLL_GET behavior, when incrementing the page's refcount.
+ *
+ * @page:	pointer to page to be grabbed
+ * @flags:	gup flags: these are the FOLL_* flag values.
+ *
+ * Either FOLL_PIN or FOLL_GET (or neither) may be set, but not both at the same
+ * time. Cases:
+ *
+ *	FOLL_GET: page's refcount will be incremented by 1.
+ *      FOLL_PIN: page's refcount will be incremented by GUP_PIN_COUNTING_BIAS.
+ *
+ * Return: true for success, or if no action was required (if neither FOLL_PIN
+ * nor FOLL_GET was set, nothing is done). False for failure: FOLL_GET or
+ * FOLL_PIN was set, but the page could not be grabbed.
+ */
+bool __must_check try_grab_page(struct page *page, unsigned int flags)
+{
+	if (flags & FOLL_GET)
+		return try_get_page(page);
+	else if (flags & FOLL_PIN) {
+		page = compound_head(page);
+		WARN_ON_ONCE(flags & FOLL_GET);
+
+		if (WARN_ON_ONCE(page_ref_zero_or_close_to_bias_overflow(page)))
+			return false;
+
+		page_ref_add(page, GUP_PIN_COUNTING_BIAS);
+		__update_proc_vmstat(page, NR_FOLL_PIN_REQUESTED, 1);
+	}
+
+	return true;
+}
+
+#ifdef CONFIG_DEV_PAGEMAP_OPS
+static bool __unpin_devmap_managed_user_page(struct page *page)
+{
+	bool is_devmap = page_is_devmap_managed(page);
+
+	if (is_devmap) {
+		int count = page_ref_sub_return(page, GUP_PIN_COUNTING_BIAS);
+
+		__update_proc_vmstat(page, NR_FOLL_PIN_RETURNED, 1);
+		/*
+		 * devmap page refcounts are 1-based, rather than 0-based: if
+		 * refcount is 1, then the page is free and the refcount is
+		 * stable because nobody holds a reference on the page.
+		 */
+		if (count == 1)
+			free_devmap_managed_page(page);
+		else if (!count)
+			__put_page(page);
+	}
+
+	return is_devmap;
+}
+#else
+static bool __unpin_devmap_managed_user_page(struct page *page)
+{
+	return false;
+}
+#endif /* CONFIG_DEV_PAGEMAP_OPS */
+
+/**
+ * unpin_user_page() - release a dma-pinned page
+ * @page:            pointer to page to be released
+ *
+ * Pages that were pinned via pin_user_pages*() must be released via either
+ * unpin_user_page(), or one of the unpin_user_pages*() routines. This is so
+ * that such pages can be separately tracked and uniquely handled. In
+ * particular, interactions with RDMA and filesystems need special handling.
+ */
+void unpin_user_page(struct page *page)
+{
+	page = compound_head(page);
+
+	/*
+	 * For devmap managed pages we need to catch refcount transition from
+	 * GUP_PIN_COUNTING_BIAS to 1, when refcount reach one it means the
+	 * page is free and we need to inform the device driver through
+	 * callback. See include/linux/memremap.h and HMM for details.
+	 */
+	if (__unpin_devmap_managed_user_page(page))
+		return;
+
+	if (page_ref_sub_and_test(page, GUP_PIN_COUNTING_BIAS))
+		__put_page(page);
+
+	__update_proc_vmstat(page, NR_FOLL_PIN_RETURNED, 1);
+}
+EXPORT_SYMBOL(unpin_user_page);
+
 /**
  * unpin_user_pages_dirty_lock() - release and optionally dirty gup-pinned pages
  * @pages:  array of pages to be maybe marked dirty, and definitely released.
@@ -237,10 +401,11 @@  static struct page *follow_page_pte(struct vm_area_struct *vma,
 	}
 
 	page = vm_normal_page(vma, address, pte);
-	if (!page && pte_devmap(pte) && (flags & FOLL_GET)) {
+	if (!page && pte_devmap(pte) && (flags & (FOLL_GET | FOLL_PIN))) {
 		/*
-		 * Only return device mapping pages in the FOLL_GET case since
-		 * they are only valid while holding the pgmap reference.
+		 * Only return device mapping pages in the FOLL_GET or FOLL_PIN
+		 * case since they are only valid while holding the pgmap
+		 * reference.
 		 */
 		*pgmap = get_dev_pagemap(pte_pfn(pte), *pgmap);
 		if (*pgmap)
@@ -278,11 +443,10 @@  static struct page *follow_page_pte(struct vm_area_struct *vma,
 		goto retry;
 	}
 
-	if (flags & FOLL_GET) {
-		if (unlikely(!try_get_page(page))) {
-			page = ERR_PTR(-ENOMEM);
-			goto out;
-		}
+	/* try_grab_page() does nothing unless FOLL_GET or FOLL_PIN is set. */
+	if (unlikely(!try_grab_page(page, flags))) {
+		page = ERR_PTR(-ENOMEM);
+		goto out;
 	}
 	if (flags & FOLL_TOUCH) {
 		if ((flags & FOLL_WRITE) &&
@@ -544,7 +708,7 @@  static struct page *follow_page_mask(struct vm_area_struct *vma,
 	/* make this handle hugepd */
 	page = follow_huge_addr(mm, address, flags & FOLL_WRITE);
 	if (!IS_ERR(page)) {
-		BUG_ON(flags & FOLL_GET);
+		WARN_ON_ONCE(flags & (FOLL_GET | FOLL_PIN));
 		return page;
 	}
 
@@ -1131,6 +1295,36 @@  static __always_inline long __get_user_pages_locked(struct task_struct *tsk,
 	return pages_done;
 }
 
+static long __get_user_pages_remote(struct task_struct *tsk,
+				    struct mm_struct *mm,
+				    unsigned long start, unsigned long nr_pages,
+				    unsigned int gup_flags, struct page **pages,
+				    struct vm_area_struct **vmas, int *locked)
+{
+	/*
+	 * Parts of FOLL_LONGTERM behavior are incompatible with
+	 * FAULT_FLAG_ALLOW_RETRY because of the FS DAX check requirement on
+	 * vmas. However, this only comes up if locked is set, and there are
+	 * callers that do request FOLL_LONGTERM, but do not set locked. So,
+	 * allow what we can.
+	 */
+	if (gup_flags & FOLL_LONGTERM) {
+		if (WARN_ON_ONCE(locked))
+			return -EINVAL;
+		/*
+		 * This will check the vmas (even if our vmas arg is NULL)
+		 * and return -ENOTSUPP if DAX isn't allowed in this case:
+		 */
+		return __gup_longterm_locked(tsk, mm, start, nr_pages, pages,
+					     vmas, gup_flags | FOLL_TOUCH |
+					     FOLL_REMOTE);
+	}
+
+	return __get_user_pages_locked(tsk, mm, start, nr_pages, pages, vmas,
+				       locked,
+				       gup_flags | FOLL_TOUCH | FOLL_REMOTE);
+}
+
 /*
  * get_user_pages_remote() - pin user pages in memory
  * @tsk:	the task_struct to use for page fault accounting, or
@@ -1205,28 +1399,8 @@  long get_user_pages_remote(struct task_struct *tsk, struct mm_struct *mm,
 	if (WARN_ON_ONCE(gup_flags & FOLL_PIN))
 		return -EINVAL;
 
-	/*
-	 * Parts of FOLL_LONGTERM behavior are incompatible with
-	 * FAULT_FLAG_ALLOW_RETRY because of the FS DAX check requirement on
-	 * vmas. However, this only comes up if locked is set, and there are
-	 * callers that do request FOLL_LONGTERM, but do not set locked. So,
-	 * allow what we can.
-	 */
-	if (gup_flags & FOLL_LONGTERM) {
-		if (WARN_ON_ONCE(locked))
-			return -EINVAL;
-		/*
-		 * This will check the vmas (even if our vmas arg is NULL)
-		 * and return -ENOTSUPP if DAX isn't allowed in this case:
-		 */
-		return __gup_longterm_locked(tsk, mm, start, nr_pages, pages,
-					     vmas, gup_flags | FOLL_TOUCH |
-					     FOLL_REMOTE);
-	}
-
-	return __get_user_pages_locked(tsk, mm, start, nr_pages, pages, vmas,
-				       locked,
-				       gup_flags | FOLL_TOUCH | FOLL_REMOTE);
+	return __get_user_pages_remote(tsk, mm, start, nr_pages, gup_flags,
+				       pages, vmas, locked);
 }
 EXPORT_SYMBOL(get_user_pages_remote);
 
@@ -1421,10 +1595,11 @@  static long __get_user_pages_locked(struct task_struct *tsk,
 	return i ? : -EFAULT;
 }
 
-long get_user_pages_remote(struct task_struct *tsk, struct mm_struct *mm,
-			   unsigned long start, unsigned long nr_pages,
-			   unsigned int gup_flags, struct page **pages,
-			   struct vm_area_struct **vmas, int *locked)
+static long __get_user_pages_remote(struct task_struct *tsk,
+				    struct mm_struct *mm,
+				    unsigned long start, unsigned long nr_pages,
+				    unsigned int gup_flags, struct page **pages,
+				    struct vm_area_struct **vmas, int *locked)
 {
 	return 0;
 }
@@ -1864,13 +2039,17 @@  static inline pte_t gup_get_pte(pte_t *ptep)
 #endif /* CONFIG_GUP_GET_PTE_LOW_HIGH */
 
 static void __maybe_unused undo_dev_pagemap(int *nr, int nr_start,
+					    unsigned int flags,
 					    struct page **pages)
 {
 	while ((*nr) - nr_start) {
 		struct page *page = pages[--(*nr)];
 
 		ClearPageReferenced(page);
-		put_page(page);
+		if (flags & FOLL_PIN)
+			unpin_user_page(page);
+		else
+			put_page(page);
 	}
 }
 
@@ -1903,7 +2082,7 @@  static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
 
 			pgmap = get_dev_pagemap(pte_pfn(pte), pgmap);
 			if (unlikely(!pgmap)) {
-				undo_dev_pagemap(nr, nr_start, pages);
+				undo_dev_pagemap(nr, nr_start, flags, pages);
 				goto pte_unmap;
 			}
 		} else if (pte_special(pte))
@@ -1912,7 +2091,7 @@  static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
 		VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
 		page = pte_page(pte);
 
-		head = try_get_compound_head(page, 1);
+		head = try_grab_compound_head(page, 1, flags);
 		if (!head)
 			goto pte_unmap;
 
@@ -1957,7 +2136,8 @@  static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
 
 #if defined(CONFIG_ARCH_HAS_PTE_DEVMAP) && defined(CONFIG_TRANSPARENT_HUGEPAGE)
 static int __gup_device_huge(unsigned long pfn, unsigned long addr,
-		unsigned long end, struct page **pages, int *nr)
+			     unsigned long end, unsigned int flags,
+			     struct page **pages, int *nr)
 {
 	int nr_start = *nr;
 	struct dev_pagemap *pgmap = NULL;
@@ -1967,12 +2147,15 @@  static int __gup_device_huge(unsigned long pfn, unsigned long addr,
 
 		pgmap = get_dev_pagemap(pfn, pgmap);
 		if (unlikely(!pgmap)) {
-			undo_dev_pagemap(nr, nr_start, pages);
+			undo_dev_pagemap(nr, nr_start, flags, pages);
 			return 0;
 		}
 		SetPageReferenced(page);
 		pages[*nr] = page;
-		get_page(page);
+		if (unlikely(!try_grab_page(page, flags))) {
+			undo_dev_pagemap(nr, nr_start, flags, pages);
+			return 0;
+		}
 		(*nr)++;
 		pfn++;
 	} while (addr += PAGE_SIZE, addr != end);
@@ -1983,48 +2166,52 @@  static int __gup_device_huge(unsigned long pfn, unsigned long addr,
 }
 
 static int __gup_device_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
-		unsigned long end, struct page **pages, int *nr)
+				 unsigned long end, unsigned int flags,
+				 struct page **pages, int *nr)
 {
 	unsigned long fault_pfn;
 	int nr_start = *nr;
 
 	fault_pfn = pmd_pfn(orig) + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
-	if (!__gup_device_huge(fault_pfn, addr, end, pages, nr))
+	if (!__gup_device_huge(fault_pfn, addr, end, flags, pages, nr))
 		return 0;
 
 	if (unlikely(pmd_val(orig) != pmd_val(*pmdp))) {
-		undo_dev_pagemap(nr, nr_start, pages);
+		undo_dev_pagemap(nr, nr_start, flags, pages);
 		return 0;
 	}
 	return 1;
 }
 
 static int __gup_device_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
-		unsigned long end, struct page **pages, int *nr)
+				 unsigned long end, unsigned int flags,
+				 struct page **pages, int *nr)
 {
 	unsigned long fault_pfn;
 	int nr_start = *nr;
 
 	fault_pfn = pud_pfn(orig) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
-	if (!__gup_device_huge(fault_pfn, addr, end, pages, nr))
+	if (!__gup_device_huge(fault_pfn, addr, end, flags, pages, nr))
 		return 0;
 
 	if (unlikely(pud_val(orig) != pud_val(*pudp))) {
-		undo_dev_pagemap(nr, nr_start, pages);
+		undo_dev_pagemap(nr, nr_start, flags, pages);
 		return 0;
 	}
 	return 1;
 }
 #else
 static int __gup_device_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
-		unsigned long end, struct page **pages, int *nr)
+				 unsigned long end, unsigned int flags,
+				 struct page **pages, int *nr)
 {
 	BUILD_BUG();
 	return 0;
 }
 
 static int __gup_device_huge_pud(pud_t pud, pud_t *pudp, unsigned long addr,
-		unsigned long end, struct page **pages, int *nr)
+				 unsigned long end, unsigned int flags,
+				 struct page **pages, int *nr)
 {
 	BUILD_BUG();
 	return 0;
@@ -2042,8 +2229,11 @@  static int record_subpages(struct page *page, unsigned long addr,
 	return nr;
 }
 
-static void put_compound_head(struct page *page, int refs)
+static void put_compound_head(struct page *page, int refs, unsigned int flags)
 {
+	if (flags & FOLL_PIN)
+		refs *= GUP_PIN_COUNTING_BIAS;
+
 	/* Do a get_page() first, in case refs == page->_refcount */
 	get_page(page);
 	page_ref_sub(page, refs);
@@ -2083,12 +2273,12 @@  static int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr,
 	page = head + ((addr & (sz-1)) >> PAGE_SHIFT);
 	refs = record_subpages(page, addr, end, pages + *nr);
 
-	head = try_get_compound_head(head, refs);
+	head = try_grab_compound_head(head, refs, flags);
 	if (!head)
 		return 0;
 
 	if (unlikely(pte_val(pte) != pte_val(*ptep))) {
-		put_compound_head(head, refs);
+		put_compound_head(head, refs, flags);
 		return 0;
 	}
 
@@ -2136,18 +2326,19 @@  static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
 	if (pmd_devmap(orig)) {
 		if (unlikely(flags & FOLL_LONGTERM))
 			return 0;
-		return __gup_device_huge_pmd(orig, pmdp, addr, end, pages, nr);
+		return __gup_device_huge_pmd(orig, pmdp, addr, end, flags,
+					     pages, nr);
 	}
 
 	page = pmd_page(orig) + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
 	refs = record_subpages(page, addr, end, pages + *nr);
 
-	head = try_get_compound_head(pmd_page(orig), refs);
+	head = try_grab_compound_head(pmd_page(orig), refs, flags);
 	if (!head)
 		return 0;
 
 	if (unlikely(pmd_val(orig) != pmd_val(*pmdp))) {
-		put_compound_head(head, refs);
+		put_compound_head(head, refs, flags);
 		return 0;
 	}
 
@@ -2157,7 +2348,8 @@  static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
 }
 
 static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
-		unsigned long end, unsigned int flags, struct page **pages, int *nr)
+			unsigned long end, unsigned int flags,
+			struct page **pages, int *nr)
 {
 	struct page *head, *page;
 	int refs;
@@ -2168,18 +2360,19 @@  static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
 	if (pud_devmap(orig)) {
 		if (unlikely(flags & FOLL_LONGTERM))
 			return 0;
-		return __gup_device_huge_pud(orig, pudp, addr, end, pages, nr);
+		return __gup_device_huge_pud(orig, pudp, addr, end, flags,
+					     pages, nr);
 	}
 
 	page = pud_page(orig) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
 	refs = record_subpages(page, addr, end, pages + *nr);
 
-	head = try_get_compound_head(pud_page(orig), refs);
+	head = try_grab_compound_head(pud_page(orig), refs, flags);
 	if (!head)
 		return 0;
 
 	if (unlikely(pud_val(orig) != pud_val(*pudp))) {
-		put_compound_head(head, refs);
+		put_compound_head(head, refs, flags);
 		return 0;
 	}
 
@@ -2203,12 +2396,12 @@  static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr,
 	page = pgd_page(orig) + ((addr & ~PGDIR_MASK) >> PAGE_SHIFT);
 	refs = record_subpages(page, addr, end, pages + *nr);
 
-	head = try_get_compound_head(pgd_page(orig), refs);
+	head = try_grab_compound_head(pgd_page(orig), refs, flags);
 	if (!head)
 		return 0;
 
 	if (unlikely(pgd_val(orig) != pgd_val(*pgdp))) {
-		put_compound_head(head, refs);
+		put_compound_head(head, refs, flags);
 		return 0;
 	}
 
@@ -2371,6 +2564,14 @@  int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
 	unsigned long len, end;
 	unsigned long flags;
 	int nr = 0;
+	/*
+	 * Internally (within mm/gup.c), gup fast variants must set FOLL_GET,
+	 * because gup fast is always a "pin with a +1 page refcount" request.
+	 */
+	unsigned int gup_flags = FOLL_GET;
+
+	if (write)
+		gup_flags |= FOLL_WRITE;
 
 	start = untagged_addr(start) & PAGE_MASK;
 	len = (unsigned long) nr_pages << PAGE_SHIFT;
@@ -2396,7 +2597,7 @@  int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
 	if (IS_ENABLED(CONFIG_HAVE_FAST_GUP) &&
 	    gup_fast_permitted(start, end)) {
 		local_irq_save(flags);
-		gup_pgd_range(start, end, write ? FOLL_WRITE : 0, pages, &nr);
+		gup_pgd_range(start, end, gup_flags, pages, &nr);
 		local_irq_restore(flags);
 	}
 
@@ -2435,7 +2636,7 @@  static int internal_get_user_pages_fast(unsigned long start, int nr_pages,
 	int nr = 0, ret = 0;
 
 	if (WARN_ON_ONCE(gup_flags & ~(FOLL_WRITE | FOLL_LONGTERM |
-				       FOLL_FORCE | FOLL_PIN)))
+				       FOLL_FORCE | FOLL_PIN | FOLL_GET)))
 		return -EINVAL;
 
 	start = untagged_addr(start) & PAGE_MASK;
@@ -2502,6 +2703,13 @@  int get_user_pages_fast(unsigned long start, int nr_pages,
 	if (WARN_ON_ONCE(gup_flags & FOLL_PIN))
 		return -EINVAL;
 
+	/*
+	 * The caller may or may not have explicitly set FOLL_GET; either way is
+	 * OK. However, internally (within mm/gup.c), gup fast variants must set
+	 * FOLL_GET, because gup fast is always a "pin with a +1 page refcount"
+	 * request.
+	 */
+	gup_flags |= FOLL_GET;
 	return internal_get_user_pages_fast(start, nr_pages, gup_flags, pages);
 }
 EXPORT_SYMBOL_GPL(get_user_pages_fast);
@@ -2509,9 +2717,12 @@  EXPORT_SYMBOL_GPL(get_user_pages_fast);
 /**
  * pin_user_pages_fast() - pin user pages in memory without taking locks
  *
- * For now, this is a placeholder function, until various call sites are
- * converted to use the correct get_user_pages*() or pin_user_pages*() API. So,
- * this is identical to get_user_pages_fast().
+ * Nearly the same as get_user_pages_fast(), except that FOLL_PIN is set. See
+ * get_user_pages_fast() for documentation on the function arguments, because
+ * the arguments here are identical.
+ *
+ * FOLL_PIN means that the pages must be released via unpin_user_page(). Please
+ * see Documentation/vm/pin_user_pages.rst for further details.
  *
  * This is intended for Case 1 (DIO) in Documentation/vm/pin_user_pages.rst. It
  * is NOT intended for Case 2 (RDMA: long-term pins).
@@ -2519,21 +2730,24 @@  EXPORT_SYMBOL_GPL(get_user_pages_fast);
 int pin_user_pages_fast(unsigned long start, int nr_pages,
 			unsigned int gup_flags, struct page **pages)
 {
-	/*
-	 * This is a placeholder, until the pin functionality is activated.
-	 * Until then, just behave like the corresponding get_user_pages*()
-	 * routine.
-	 */
-	return get_user_pages_fast(start, nr_pages, gup_flags, pages);
+	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
+	if (WARN_ON_ONCE(gup_flags & FOLL_GET))
+		return -EINVAL;
+
+	gup_flags |= FOLL_PIN;
+	return internal_get_user_pages_fast(start, nr_pages, gup_flags, pages);
 }
 EXPORT_SYMBOL_GPL(pin_user_pages_fast);
 
 /**
  * pin_user_pages_remote() - pin pages of a remote process (task != current)
  *
- * For now, this is a placeholder function, until various call sites are
- * converted to use the correct get_user_pages*() or pin_user_pages*() API. So,
- * this is identical to get_user_pages_remote().
+ * Nearly the same as get_user_pages_remote(), except that FOLL_PIN is set. See
+ * get_user_pages_remote() for documentation on the function arguments, because
+ * the arguments here are identical.
+ *
+ * FOLL_PIN means that the pages must be released via unpin_user_page(). Please
+ * see Documentation/vm/pin_user_pages.rst for details.
  *
  * This is intended for Case 1 (DIO) in Documentation/vm/pin_user_pages.rst. It
  * is NOT intended for Case 2 (RDMA: long-term pins).
@@ -2543,22 +2757,24 @@  long pin_user_pages_remote(struct task_struct *tsk, struct mm_struct *mm,
 			   unsigned int gup_flags, struct page **pages,
 			   struct vm_area_struct **vmas, int *locked)
 {
-	/*
-	 * This is a placeholder, until the pin functionality is activated.
-	 * Until then, just behave like the corresponding get_user_pages*()
-	 * routine.
-	 */
-	return get_user_pages_remote(tsk, mm, start, nr_pages, gup_flags, pages,
-				     vmas, locked);
+	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
+	if (WARN_ON_ONCE(gup_flags & FOLL_GET))
+		return -EINVAL;
+
+	gup_flags |= FOLL_PIN;
+	return __get_user_pages_remote(tsk, mm, start, nr_pages, gup_flags,
+				       pages, vmas, locked);
 }
 EXPORT_SYMBOL(pin_user_pages_remote);
 
 /**
  * pin_user_pages() - pin user pages in memory for use by other devices
  *
- * For now, this is a placeholder function, until various call sites are
- * converted to use the correct get_user_pages*() or pin_user_pages*() API. So,
- * this is identical to get_user_pages().
+ * Nearly the same as get_user_pages(), except that FOLL_TOUCH is not set, and
+ * FOLL_PIN is set.
+ *
+ * FOLL_PIN means that the pages must be released via unpin_user_page(). Please
+ * see Documentation/vm/pin_user_pages.rst for details.
  *
  * This is intended for Case 1 (DIO) in Documentation/vm/pin_user_pages.rst. It
  * is NOT intended for Case 2 (RDMA: long-term pins).
@@ -2567,11 +2783,12 @@  long pin_user_pages(unsigned long start, unsigned long nr_pages,
 		    unsigned int gup_flags, struct page **pages,
 		    struct vm_area_struct **vmas)
 {
-	/*
-	 * This is a placeholder, until the pin functionality is activated.
-	 * Until then, just behave like the corresponding get_user_pages*()
-	 * routine.
-	 */
-	return get_user_pages(start, nr_pages, gup_flags, pages, vmas);
+	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
+	if (WARN_ON_ONCE(gup_flags & FOLL_GET))
+		return -EINVAL;
+
+	gup_flags |= FOLL_PIN;
+	return __gup_longterm_locked(current, current->mm, start, nr_pages,
+				     pages, vmas, gup_flags);
 }
 EXPORT_SYMBOL(pin_user_pages);
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 41a0fbddc96b..ebaa6961ff76 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -945,6 +945,11 @@  struct page *follow_devmap_pmd(struct vm_area_struct *vma, unsigned long addr,
 	 */
 	WARN_ONCE(flags & FOLL_COW, "mm: In follow_devmap_pmd with FOLL_COW set");
 
+	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
+	if (WARN_ON_ONCE((flags & (FOLL_PIN | FOLL_GET)) ==
+			 (FOLL_PIN | FOLL_GET)))
+		return NULL;
+
 	if (flags & FOLL_WRITE && !pmd_write(*pmd))
 		return NULL;
 
@@ -960,7 +965,7 @@  struct page *follow_devmap_pmd(struct vm_area_struct *vma, unsigned long addr,
 	 * device mapped pages can only be returned if the
 	 * caller will manage the page reference count.
 	 */
-	if (!(flags & FOLL_GET))
+	if (!(flags & (FOLL_GET | FOLL_PIN)))
 		return ERR_PTR(-EEXIST);
 
 	pfn += (addr & ~PMD_MASK) >> PAGE_SHIFT;
@@ -968,7 +973,8 @@  struct page *follow_devmap_pmd(struct vm_area_struct *vma, unsigned long addr,
 	if (!*pgmap)
 		return ERR_PTR(-EFAULT);
 	page = pfn_to_page(pfn);
-	get_page(page);
+	if (!try_grab_page(page, flags))
+		page = ERR_PTR(-EFAULT);
 
 	return page;
 }
@@ -1088,6 +1094,11 @@  struct page *follow_devmap_pud(struct vm_area_struct *vma, unsigned long addr,
 	if (flags & FOLL_WRITE && !pud_write(*pud))
 		return NULL;
 
+	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
+	if (WARN_ON_ONCE((flags & (FOLL_PIN | FOLL_GET)) ==
+			 (FOLL_PIN | FOLL_GET)))
+		return NULL;
+
 	if (pud_present(*pud) && pud_devmap(*pud))
 		/* pass */;
 	else
@@ -1099,8 +1110,10 @@  struct page *follow_devmap_pud(struct vm_area_struct *vma, unsigned long addr,
 	/*
 	 * device mapped pages can only be returned if the
 	 * caller will manage the page reference count.
+	 *
+	 * At least one of FOLL_GET | FOLL_PIN must be set, so assert that here:
 	 */
-	if (!(flags & FOLL_GET))
+	if (!(flags & (FOLL_GET | FOLL_PIN)))
 		return ERR_PTR(-EEXIST);
 
 	pfn += (addr & ~PUD_MASK) >> PAGE_SHIFT;
@@ -1108,7 +1121,8 @@  struct page *follow_devmap_pud(struct vm_area_struct *vma, unsigned long addr,
 	if (!*pgmap)
 		return ERR_PTR(-EFAULT);
 	page = pfn_to_page(pfn);
-	get_page(page);
+	if (!try_grab_page(page, flags))
+		page = ERR_PTR(-EFAULT);
 
 	return page;
 }
@@ -1468,6 +1482,7 @@  struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
 {
 	struct mm_struct *mm = vma->vm_mm;
 	struct page *page = NULL;
+	struct page *subpage = NULL;
 
 	assert_spin_locked(pmd_lockptr(mm, pmd));
 
@@ -1486,6 +1501,14 @@  struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
 	VM_BUG_ON_PAGE(!PageHead(page) && !is_zone_device_page(page), page);
 	if (flags & FOLL_TOUCH)
 		touch_pmd(vma, addr, pmd, flags);
+
+	subpage = page;
+	subpage += (addr & ~HPAGE_PMD_MASK) >> PAGE_SHIFT;
+	VM_BUG_ON_PAGE(!PageCompound(subpage) &&
+		       !is_zone_device_page(subpage), subpage);
+	if (!try_grab_page(subpage, flags))
+		return ERR_PTR(-EFAULT);
+
 	if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) {
 		/*
 		 * We don't mlock() pte-mapped THPs. This way we can avoid
@@ -1509,24 +1532,18 @@  struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
 		 */
 
 		if (PageAnon(page) && compound_mapcount(page) != 1)
-			goto skip_mlock;
+			goto out;
 		if (PageDoubleMap(page) || !page->mapping)
-			goto skip_mlock;
+			goto out;
 		if (!trylock_page(page))
-			goto skip_mlock;
+			goto out;
 		lru_add_drain();
 		if (page->mapping && !PageDoubleMap(page))
 			mlock_vma_page(page);
 		unlock_page(page);
 	}
-skip_mlock:
-	page += (addr & ~HPAGE_PMD_MASK) >> PAGE_SHIFT;
-	VM_BUG_ON_PAGE(!PageCompound(page) && !is_zone_device_page(page), page);
-	if (flags & FOLL_GET)
-		get_page(page);
-
 out:
-	return page;
+	return subpage;
 }
 
 /* NUMA hinting page fault entry point for trans huge pmds */
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index ac65bb5e38ac..0e21bbe9f017 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -4326,19 +4326,6 @@  long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
 		pfn_offset = (vaddr & ~huge_page_mask(h)) >> PAGE_SHIFT;
 		page = pte_page(huge_ptep_get(pte));
 
-		/*
-		 * Instead of doing 'try_get_page()' below in the same_page
-		 * loop, just check the count once here.
-		 */
-		if (unlikely(page_count(page) <= 0)) {
-			if (pages) {
-				spin_unlock(ptl);
-				remainder = 0;
-				err = -ENOMEM;
-				break;
-			}
-		}
-
 		/*
 		 * If subpage information not requested, update counters
 		 * and skip the same_page loop below.
@@ -4356,7 +4343,13 @@  long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
 same_page:
 		if (pages) {
 			pages[i] = mem_map_offset(page, pfn_offset);
-			get_page(pages[i]);
+			if (!try_grab_page(pages[i], flags)) {
+				spin_unlock(ptl);
+				remainder = 0;
+				err = -ENOMEM;
+				WARN_ON_ONCE(1);
+				break;
+			}
 		}
 
 		if (vmas)
@@ -4916,6 +4909,12 @@  follow_huge_pmd(struct mm_struct *mm, unsigned long address,
 	struct page *page = NULL;
 	spinlock_t *ptl;
 	pte_t pte;
+
+	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
+	if (WARN_ON_ONCE((flags & (FOLL_PIN | FOLL_GET)) ==
+			 (FOLL_PIN | FOLL_GET)))
+		return NULL;
+
 retry:
 	ptl = pmd_lockptr(mm, pmd);
 	spin_lock(ptl);
@@ -4928,8 +4927,11 @@  follow_huge_pmd(struct mm_struct *mm, unsigned long address,
 	pte = huge_ptep_get((pte_t *)pmd);
 	if (pte_present(pte)) {
 		page = pmd_page(*pmd) + ((address & ~PMD_MASK) >> PAGE_SHIFT);
-		if (flags & FOLL_GET)
-			get_page(page);
+		if (unlikely(!try_grab_page(page, flags))) {
+			WARN_ON_ONCE(1);
+			page = NULL;
+			goto out;
+		}
 	} else {
 		if (is_hugetlb_entry_migration(pte)) {
 			spin_unlock(ptl);
@@ -4950,7 +4952,7 @@  struct page * __weak
 follow_huge_pud(struct mm_struct *mm, unsigned long address,
 		pud_t *pud, int flags)
 {
-	if (flags & FOLL_GET)
+	if (flags & (FOLL_GET | FOLL_PIN))
 		return NULL;
 
 	return pte_page(*(pte_t *)pud) + ((address & ~PUD_MASK) >> PAGE_SHIFT);
@@ -4959,7 +4961,7 @@  follow_huge_pud(struct mm_struct *mm, unsigned long address,
 struct page * __weak
 follow_huge_pgd(struct mm_struct *mm, unsigned long address, pgd_t *pgd, int flags)
 {
-	if (flags & FOLL_GET)
+	if (flags & (FOLL_GET | FOLL_PIN))
 		return NULL;
 
 	return pte_page(*(pte_t *)pgd) + ((address & ~PGDIR_MASK) >> PAGE_SHIFT);
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 78d53378db99..b56808bae1b4 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1168,6 +1168,8 @@  const char * const vmstat_text[] = {
 	"nr_dirtied",
 	"nr_written",
 	"nr_kernel_misc_reclaimable",
+	"nr_foll_pin_requested",
+	"nr_foll_pin_returned",
 
 	/* enum writeback_stat_item counters */
 	"nr_dirty_threshold",