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>

6 files changed, 16 insertions, 29 deletions

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 63c9cafda9c4..587da5e0990f 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -42,9 +42,6 @@ config GENERIC_HARDIRQS
         bool
         default y
 
-config HAVE_GET_USER_PAGES_FAST
-        def_bool PPC64
-
 config HAVE_SETUP_PER_CPU_AREA
         def_bool PPC64
 
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 3d0f2b6a5a16..ac2fb0641a04 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -22,7 +22,6 @@ config X86
         select HAVE_IDE
         select HAVE_OPROFILE
         select HAVE_IOREMAP_PROT
-        select HAVE_GET_USER_PAGES_FAST
         select HAVE_KPROBES
         select ARCH_WANT_OPTIONAL_GPIOLIB
         select HAVE_KRETPROBES
diff --git a/arch/x86/mm/Makefile b/arch/x86/mm/Makefile
index 2977ea37791f..dfb932dcf136 100644
--- a/arch/x86/mm/Makefile
+++ b/arch/x86/mm/Makefile
@@ -1,7 +1,6 @@
 obj-y   :=  init_$(BITS).o fault.o ioremap.o extable.o pageattr.o mmap.o \
-            pat.o pgtable.o
+            pat.o pgtable.o gup.o
 
-obj-$(CONFIG_HAVE_GET_USER_PAGES_FAST) += gup.o
 obj-$(CONFIG_X86_32)            += pgtable_32.o
 
 obj-$(CONFIG_HUGETLB_PAGE)      += hugetlbpage.o
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 335288bff1b7..fa651609b65d 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -834,7 +834,6 @@ extern int mprotect_fixup(struct vm_area_struct *vma,
                           struct vm_area_struct **pprev, unsigned long start,
                           unsigned long end, unsigned long newflags);
 
-#ifdef CONFIG_HAVE_GET_USER_PAGES_FAST
 /*
  * get_user_pages_fast provides equivalent functionality to get_user_pages,
  * operating on current and current->mm (force=0 and doesn't return any vmas).
@@ -848,25 +847,6 @@ extern int mprotect_fixup(struct vm_area_struct *vma,
 int get_user_pages_fast(unsigned long start, int nr_pages, int write,
                         struct page **pages);
 
-#else
-/*
- * Should probably be moved to asm-generic, and architectures can include it if
- * they don't implement their own get_user_pages_fast.
- */
-#define get_user_pages_fast(start, nr_pages, write, 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);                                 \
-                                                                \
-        ret;                                                    \
-})
-#endif
-
 /*
  * A callback you can register to apply pressure to ageable caches.
  *
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);