[PATCH v7 17/24] mm/gup: track FOLL_PIN pages

John Hubbard
2019-11-21T07:14:13Z

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 put_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>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
Documentation/core-api/pin_user_pages.rst | 2 +-
include/linux/mm.h | 113 +++++++-
include/linux/mmzone.h | 2 +
include/linux/page_ref.h | 10 +
mm/gup.c | 323 ++++++++++++++++------
mm/huge_memory.c | 44 ++-
mm/hugetlb.c | 36 ++-
mm/vmstat.c | 2 +
8 files changed, 421 insertions(+), 111 deletions(-)

diff --git a/Documentation/core-api/pin_user_pages.rst b/Documentation/core-api/pin_user_pages.rst
index 4f26637a5005..baa288a44a77 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 568cbb895f03..253ec2d15f36 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1054,6 +1054,21 @@ static inline __must_check bool try_get_page(struct page *page)
return true;
}

+__must_check bool try_pin_compound_head(struct page *page, int refs);
+
+/**
+ * try_pin_page() - mark a page as being used by pin_user_pages*().
+ *
+ * This is the FOLL_PIN counterpart to try_get_page().
+ *
+ * @page: pointer to page to be marked
+ * @Return: true for success, false for failure
+ */
+static inline __must_check bool try_pin_page(struct page *page)
+{
+ return try_pin_compound_head(page, 1);
+}
+
static inline void put_page(struct page *page)
{
page = compound_head(page);
@@ -1071,29 +1086,70 @@ static inline void put_page(struct page *page)
__put_page(page);
}

-/**
- * put_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).
*
- * Pages that were pinned via pin_user_pages*() must be released via either
- * put_user_page(), or one of the put_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.
+ * With this scheme, pin_user_pages() becomes special: such pages are marked as
+ * distinct from normal pages. As such, the put_user_page() call (and its
+ * variants) must be used in order to release gup-pinned pages.
*
- * put_user_page() and put_page() are not interchangeable, despite this early
- * implementation that makes them look the same. put_user_page() calls must
- * be perfectly matched up with pin*() calls.
+ * Choice of value:
+ *
+ * By making GUP_PIN_COUNTING_BIAS a power of two, debugging of page reference
+ * counts with respect to pin_user_pages() and put_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 put_user_page(struct page *page)
-{
- put_page(page);
-}
+#define GUP_PIN_COUNTING_BIAS (1UL << 10)

+void put_user_page(struct page *page);
void put_user_pages_dirty_lock(struct page **pages, unsigned long npages,
bool make_dirty);
-
void put_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
@@ -2675,6 +2731,33 @@ struct page *follow_page(struct vm_area_struct *vma, unsigned long address,
* Please see Documentation/vm/pin_user_pages.rst for more information.
*/

+/**
+ * grab_page() - elevate a page's refcount by a flag-dependent amount
+ *
+ * @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. (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: true for for success, false for failure. If neither FOLL_GET nor
+ * FOLL_PIN is set, that's also considered "success", even though nothing is
+ * done: no page refcount changes are made in that case.
+ */
+static inline bool grab_page(struct page *page, unsigned int flags)
+{
+ if (flags & FOLL_GET)
+ get_page(page);
+ else if (flags & FOLL_PIN)
+ return try_pin_page(page);
+
+ return true;
+}
+
static inline int vm_fault_to_errno(vm_fault_t vm_fault, int foll_flags)
{
if (vm_fault & VM_FAULT_OOM)
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index bda20282746b..0485cba38d23 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 put_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 f72d7a1635b4..b06434185e33 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -51,6 +51,96 @@ static inline struct page *try_get_compound_head(struct page *page, int refs)
return head;
}

+#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
+
+/**
+ * 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: true for success, false for failure
+ */
+__must_check bool try_pin_compound_head(struct page *page, int refs)
+{
+ page = try_get_compound_head(page, GUP_PIN_COUNTING_BIAS * refs);
+ if (!page)
+ return false;
+
+ __update_proc_vmstat(page, NR_FOLL_PIN_REQUESTED, refs);
+ return true;
+}
+
+#ifdef CONFIG_DEV_PAGEMAP_OPS
+static bool __put_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 __put_devmap_managed_user_page(struct page *page)
+{
+ return false;
+}
+#endif /* CONFIG_DEV_PAGEMAP_OPS */
+
+/**
+ * put_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
+ * put_user_page(), or one of the put_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 put_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 (__put_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(put_user_page);
+
/**
* put_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 +327,11 @@ 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)
@@ -283,6 +374,11 @@ static struct page *follow_page_pte(struct vm_area_struct *vma,
page = ERR_PTR(-ENOMEM);
goto out;
}
+ } else if (flags & FOLL_PIN) {
+ if (unlikely(!try_pin_page(page))) {
+ page = ERR_PTR(-ENOMEM);
+ goto out;
+ }
}
if (flags & FOLL_TOUCH) {
if ((flags & FOLL_WRITE) &&
@@ -544,8 +640,8 @@ 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);
- return page;
+ WARN_ON_ONCE(flags & (FOLL_GET | FOLL_PIN));
+ return NULL;
}

pgd = pgd_offset(mm, address);
@@ -1125,6 +1221,36 @@ 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
@@ -1193,28 +1319,8 @@ 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);

@@ -1842,13 +1948,17 @@ 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)
+ put_user_page(page);
+ else
+ put_page(page);
}
}

@@ -1881,7 +1991,7 @@ 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))
@@ -1890,9 +2000,15 @@ 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);
- if (!head)
- goto pte_unmap;
+ if (flags & FOLL_PIN) {
+ head = page;
+ if (unlikely(!try_pin_page(head)))
+ goto pte_unmap;
+ } else {
+ head = try_get_compound_head(page, 1);
+ if (!head)
+ goto pte_unmap;
+ }

if (unlikely(pte_val(pte) != pte_val(*ptep))) {
put_page(head);
@@ -1946,12 +2062,20 @@ 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 (flags & FOLL_PIN) {
+ if (unlikely(!try_pin_page(page))) {
+ undo_dev_pagemap(nr, nr_start, flags, pages);
+ return 0;
+ }
+ } else
+ get_page(page);
+
(*nr)++;
pfn++;
} while (addr += PAGE_SIZE, addr != end);
@@ -1973,7 +2097,7 @@ static int __gup_device_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
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;
@@ -1991,7 +2115,7 @@ static int __gup_device_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
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;
@@ -2014,8 +2138,8 @@ static int __gup_device_huge_pud(pud_t pud, pud_t *pudp, unsigned long addr,
}
#endif

-static int __record_subpages(struct page *page, unsigned long addr,
- unsigned long end, struct page **pages)
+static int record_subpages(struct page *page, unsigned long addr,
+ unsigned long end, struct page **pages)
{
int nr;

@@ -2025,12 +2149,31 @@ static int __record_subpages(struct page *page, unsigned long addr,
return nr;
}

-static void put_compound_head(struct page *page, int refs)
+static bool grab_compound_head(struct page *head, int refs, unsigned int flags)
{
+ if (flags & FOLL_PIN) {
+ if (unlikely(!try_pin_compound_head(head, refs)))
+ return false;
+ } else {
+ head = try_get_compound_head(head, refs);
+ if (!head)
+ return false;
+ }
+
+ return true;
+}
+
+static void put_compound_head(struct page *page, int refs, unsigned int flags)
+{
+ struct page *head = compound_head(page);
+
+ 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);
- put_page(page);
+ get_page(head);
+ page_ref_sub(head, refs);
+ put_page(head);
}

#ifdef CONFIG_ARCH_HAS_HUGEPD
@@ -2064,14 +2207,13 @@ static int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr,

head = pte_page(pte);
page = head + ((addr & (sz-1)) >> PAGE_SHIFT);
- refs = __record_subpages(page, addr, end, pages + *nr);
+ refs = record_subpages(page, addr, end, pages + *nr);

- head = try_get_compound_head(head, refs);
- if (!head)
+ if (!grab_compound_head(head, refs, flags))
return 0;

if (unlikely(pte_val(pte) != pte_val(*ptep))) {
- put_compound_head(head, refs);
+ put_compound_head(head, refs, flags);
return 0;
}

@@ -2124,14 +2266,14 @@ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
}

page = pmd_page(orig) + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
- refs = __record_subpages(page, addr, end, pages + *nr);
+ refs = record_subpages(page, addr, end, pages + *nr);

- head = try_get_compound_head(pmd_page(orig), refs);
- if (!head)
+ head = pmd_page(orig);
+ if (!grab_compound_head(head, refs, flags))
return 0;

if (unlikely(pmd_val(orig) != pmd_val(*pmdp))) {
- put_compound_head(head, refs);
+ put_compound_head(head, refs, flags);
return 0;
}

@@ -2158,14 +2300,14 @@ static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
}

page = pud_page(orig) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
- refs = __record_subpages(page, addr, end, pages + *nr);
+ refs = record_subpages(page, addr, end, pages + *nr);

- head = try_get_compound_head(pud_page(orig), refs);
- if (!head)
+ head = pud_page(orig);
+ if (!grab_compound_head(head, refs, flags))
return 0;

if (unlikely(pud_val(orig) != pud_val(*pudp))) {
- put_compound_head(head, refs);
+ put_compound_head(head, refs, flags);
return 0;
}

@@ -2187,14 +2329,14 @@ static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr,
BUILD_BUG_ON(pgd_devmap(orig));

page = pgd_page(orig) + ((addr & ~PGDIR_MASK) >> PAGE_SHIFT);
- refs = __record_subpages(page, addr, end, pages + *nr);
+ refs = record_subpages(page, addr, end, pages + *nr);

- head = try_get_compound_head(pgd_page(orig), refs);
- if (!head)
+ head = pgd_page(orig);
+ if (!grab_compound_head(head, refs, flags))
return 0;

if (unlikely(pgd_val(orig) != pgd_val(*pgdp))) {
- put_compound_head(head, refs);
+ put_compound_head(head, refs, flags);
return 0;
}

@@ -2494,9 +2636,12 @@ 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).
@@ -2504,21 +2649,24 @@ 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).
@@ -2528,22 +2676,24 @@ 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).
@@ -2552,11 +2702,12 @@ 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 13cc93785006..981a9ea0b83f 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 +973,14 @@ 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);
+
+ /*
+ * grab_page() is not actually expected to fail here because we hold the
+ * pmd lock, so no one can unmap the pmd and free the page that it
+ * points to.
+ */
+ if (!grab_page(page, flags))
+ page = ERR_PTR(-EFAULT);

return page;
}
@@ -1088,6 +1100,11 @@ 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 +1116,10 @@ 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 +1127,14 @@ 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);
+
+ /*
+ * grab_page() is not actually expected to fail here because we hold the
+ * pmd lock, so no one can unmap the pmd and free the page that it
+ * points to.
+ */
+ if (!grab_page(page, flags))
+ page = ERR_PTR(-EFAULT);

return page;
}
@@ -1522,8 +1548,14 @@ struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
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);
+
+ /*
+ * grab_page() is not actually expected to fail here because we hold the
+ * pmd lock, so no one can unmap the pmd and free the page that it
+ * points to.
+ */
+ if (!grab_page(page, flags))
+ page = ERR_PTR(-EFAULT);

out:
return page;
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index b45a95363a84..eac3310d62f5 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -4462,7 +4462,19 @@ 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]);
+
+ /*
+ * grab_page() is not actually expected to fail here
+ * because we hold the pmd lock, so no one can unmap the
+ * pmd and free the page that it points to.
+ */
+ if (!grab_page(pages[i], flags)) {
+ spin_unlock(ptl);
+ remainder = 0;
+ err = -ENOMEM;
+ WARN_ON_ONCE(1);
+ break;
+ }
}

if (vmas)
@@ -5022,6 +5034,12 @@ 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);
@@ -5034,8 +5052,20 @@ 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);
+ else if (flags & FOLL_PIN) {
+ /*
+ * try_pin_page() is not actually expected to fail
+ * here because we hold the ptl.
+ */
+ if (unlikely(!try_pin_page(page))) {
+ WARN_ON_ONCE(1);
+ page = NULL;
+ goto out;
+ }
+ }
} else {
if (is_hugetlb_entry_migration(pte)) {
spin_unlock(ptl);
@@ -5056,7 +5086,7 @@ 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);
@@ -5065,7 +5095,7 @@ 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 a8222041bd44..fdad40ccde7b 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1167,6 +1167,8 @@ 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",
--
2.24.0