[PATCH v11 23/25] mm/gup: track FOLL_PIN pages

From: John Hubbard
Date: Mon Dec 16 2019 - 17:26:04 EST

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/

Reviewed-by: Jan Kara <jack@xxxxxxx>
Suggested-by: Jan Kara <jack@xxxxxxx>
Suggested-by: JÃrÃme Glisse <jglisse@xxxxxxxxxx>
Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Signed-off-by: John Hubbard <jhubbard@xxxxxxxxxx>
---
Documentation/core-api/pin_user_pages.rst | 2 +-
include/linux/mm.h | 83 ++++-
include/linux/mmzone.h | 2 +
include/linux/page_ref.h | 10 +
mm/gup.c | 409 +++++++++++++++++-----
mm/huge_memory.c | 29 +-
mm/hugetlb.c | 38 +-
mm/vmstat.c | 2 +
8 files changed, 439 insertions(+), 136 deletions(-)

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..bb44c4d2ada7 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1016,6 +1016,8 @@ 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 +1046,80 @@ 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.
+ *
+ * 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 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).
*
- * 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.
+ * 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.
*
- * 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.
+ * 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)
+{
+ /*
+ * page_ref_count() is signed. If that refcount overflows, then
+ * page_ref_count() returns a negative value, and callers will avoid
+ * further incrementing the refcount.
+ *
+ * Here, for that overflow case, use the signed bit to count a little
+ * bit higher via unsigned math, and thus still get an accurate result
+ * from page_dma_pinned().
+ */
+ return ((unsigned int)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..c2793a86450e 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(1);
+ 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_count(page) <= 0))
+ 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;
@@ -2478,11 +2679,11 @@ static int internal_get_user_pages_fast(unsigned long start, int nr_pages,

/**
* get_user_pages_fast() - pin user pages in memory
- * @start: starting user address
- * @nr_pages: number of pages from start to pin
- * @gup_flags: flags modifying pin behaviour
- * @pages: array that receives pointers to the pages pinned.
- * Should be at least nr_pages long.
+ * @start: starting user address
+ * @nr_pages: number of pages from start to pin
+ * @gup_flags: flags modifying pin behaviour
+ * @pages: array that receives pointers to the pages pinned.
+ * Should be at least nr_pages long.
*
* Attempt to pin user pages in memory without taking mm->mmap_sem.
* If not successful, it will fall back to taking the lock and
@@ -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..a71646a4c4d4 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(-ENOMEM);

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(-ENOMEM);

return page;
}
@@ -1484,8 +1498,13 @@ struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,

page = pmd_page(*pmd);
VM_BUG_ON_PAGE(!PageHead(page) && !is_zone_device_page(page), page);
+
+ if (!try_grab_page(page, flags))
+ return ERR_PTR(-ENOMEM);
+
if (flags & FOLL_TOUCH)
touch_pmd(vma, addr, pmd, flags);
+
if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) {
/*
* We don't mlock() pte-mapped THPs. This way we can avoid
@@ -1522,8 +1541,6 @@ 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);

out:
return page;
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",
--
2.24.1