mm: Make generic weak get_user_pages_fast and EXPORT_GPL it

Out of line get_user_pages_fast fallback implementation, make it a weak
symbol, get rid of CONFIG_HAVE_GET_USER_PAGES_FAST.

Export the symbol to modules so lguest can use it.

Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

2 files changed, 15 insertions, 3 deletions

diff --git a/mm/Kconfig b/mm/Kconfig
index 446c6588c753..0bd9c2dbb2a0 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -77,9 +77,6 @@ config FLAT_NODE_MEM_MAP
         def_bool y
         depends on !SPARSEMEM
 
-config HAVE_GET_USER_PAGES_FAST
-        bool
-
 #
 # Both the NUMA code and DISCONTIGMEM use arrays of pg_data_t's
 # to represent different areas of memory.  This variable allows
diff --git a/mm/util.c b/mm/util.c
index 9341ca77bd88..cb00b748ce47 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -171,3 +171,18 @@ void arch_pick_mmap_layout(struct mm_struct *mm)
         mm->unmap_area = arch_unmap_area;
 }
 #endif
+
+int __attribute__((weak)) get_user_pages_fast(unsigned long start,
+                                int nr_pages, int write, struct page **pages)
+{
+        struct mm_struct *mm = current->mm;
+        int ret;
+
+        down_read(&mm->mmap_sem);
+        ret = get_user_pages(current, mm, start, nr_pages,
+                                        write, 0, pages, NULL);
+        up_read(&mm->mmap_sem);
+
+        return ret;
+}
+EXPORT_SYMBOL_GPL(get_user_pages_fast);