mm: introduce put_user_page*(), placeholder versions

[linux.git] / include / linux / mm.h

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 083d7b4863edaba800d7d11d4fbf779acf4f11e4..e6b6be15609ec4cddadcbca0c5b3f4b107fd4b1a 100644 (file)
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1007,6 +1007,30 @@ 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
+ *
+ * Pages that were pinned via get_user_pages*() must be released via
+ * either put_user_page(), or one of the put_user_pages*() routines
+ * below. This is so that eventually, pages that are pinned via
+ * get_user_pages*() can be separately tracked and uniquely handled. In
+ * particular, interactions with RDMA and filesystems need special
+ * handling.
+ *
+ * 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 get_user_page() calls.
+ */
+static inline void put_user_page(struct page *page)
+{
+       put_page(page);
+}
+
+void put_user_pages_dirty(struct page **pages, unsigned long npages);
+void put_user_pages_dirty_lock(struct page **pages, unsigned long npages);
+void put_user_pages(struct page **pages, unsigned long npages);
+
 #if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP)
 #define SECTION_IN_PAGE_FLAGS
 #endif
@@ -1505,21 +1529,8 @@ long get_user_pages_locked(unsigned long start, unsigned long nr_pages,
 long get_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
                    struct page **pages, unsigned int gup_flags);
 
-#if defined(CONFIG_FS_DAX) || defined(CONFIG_CMA)
-long get_user_pages_longterm(unsigned long start, unsigned long nr_pages,
-                           unsigned int gup_flags, struct page **pages,
-                           struct vm_area_struct **vmas);
-#else
-static inline long get_user_pages_longterm(unsigned long start,
-               unsigned long nr_pages, unsigned int gup_flags,
-               struct page **pages, struct vm_area_struct **vmas)
-{
-       return get_user_pages(start, nr_pages, gup_flags, pages, vmas);
-}
-#endif /* CONFIG_FS_DAX */
-
-int get_user_pages_fast(unsigned long start, int nr_pages, int write,
-                       struct page **pages);
+int get_user_pages_fast(unsigned long start, int nr_pages,
+                       unsigned int gup_flags, struct page **pages);
 
 /* Container for pinned pfns / pages */
 struct frame_vector {
@@ -2583,6 +2594,34 @@ struct page *follow_page(struct vm_area_struct *vma, unsigned long address,
 #define FOLL_REMOTE    0x2000  /* we are working on non-current tsk/mm */
 #define FOLL_COW       0x4000  /* internal GUP flag */
 #define FOLL_ANON      0x8000  /* don't do file mappings */
+#define FOLL_LONGTERM  0x10000 /* mapping lifetime is indefinite: see below */
+
+/*
+ * NOTE on FOLL_LONGTERM:
+ *
+ * FOLL_LONGTERM indicates that the page will be held for an indefinite time
+ * period _often_ under userspace control.  This is contrasted with
+ * iov_iter_get_pages() where usages which are transient.
+ *
+ * FIXME: For pages which are part of a filesystem, mappings are subject to the
+ * lifetime enforced by the filesystem and we need guarantees that longterm
+ * users like RDMA and V4L2 only establish mappings which coordinate usage with
+ * the filesystem.  Ideas for this coordination include revoking the longterm
+ * pin, delaying writeback, bounce buffer page writeback, etc.  As FS DAX was
+ * added after the problem with filesystems was found FS DAX VMAs are
+ * specifically failed.  Filesystem pages are still subject to bugs and use of
+ * FOLL_LONGTERM should be avoided on those pages.
+ *
+ * FIXME: Also NOTE that FOLL_LONGTERM is not supported in every GUP call.
+ * Currently only get_user_pages() and get_user_pages_fast() support this flag
+ * and calls to get_user_pages_[un]locked are specifically not allowed.  This
+ * is due to an incompatibility with the FS DAX check and
+ * FAULT_FLAG_ALLOW_RETRY
+ *
+ * In the CMA case: longterm pins in a CMA region would unnecessarily fragment
+ * that region.  And so CMA attempts to migrate the page before pinning when
+ * FOLL_LONGTERM is specified.
+ */
 
 static inline int vm_fault_to_errno(vm_fault_t vm_fault, int foll_flags)
 {