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>

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
 

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

arch/x86/mm/Makefile

 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

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.
  *

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

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);