Cross Memory Attach: make it Kconfigurable

Add a Kconfig option to allow people who don't want cross memory attach to
not have it included in their build.

Signed-off-by: Chris Yeoh <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

mm/Kconfig

···
 	  benefit.
 endchoice
 
+config CROSS_MEMORY_ATTACH
+	bool "Cross Memory Support"
+	depends on MMU
+	default y
+	help
+	  Enabling this option adds the system calls process_vm_readv and
+	  process_vm_writev which allow a process with the correct privileges
+	  to directly read from or write to to another process's address space.
+	  See the man page for more details.
+
 #
 # UP and nommu archs use km based percpu allocator
 #

mm/Makefile

···
 mmu-y			:= nommu.o
 mmu-$(CONFIG_MMU)	:= fremap.o highmem.o madvise.o memory.o mincore.o \
 			   mlock.o mmap.o mprotect.o mremap.o msync.o rmap.o \
-			   vmalloc.o pagewalk.o pgtable-generic.o \
-			   process_vm_access.o
+			   vmalloc.o pagewalk.o pgtable-generic.o
+
+ifdef CONFIG_CROSS_MEMORY_ATTACH
+mmu-$(CONFIG_MMU)	+= process_vm_access.o
+endif
 
 obj-y			:= filemap.o mempool.o oom_kill.o fadvise.o \
 			   maccess.o page_alloc.o page-writeback.o \