[PATCH for-mm 2/2] mm/gup: Make migrate_device_page() fails always if !CONFIG_DEVICE_PRIVATE

[SeongJae Park <sj@kernel.org>]

Commit 7059ac82be44 ("mm/gup.c: migrate device coherent pages when
pinning instead of failing") in -mm tree[1] introduces
'migrate_device_page()', which uses several functions that defined under
CONFIG_DEVICE_RIVATE.  As a result, build under 'CONFIG_MIGRATION &&
!CONFIG_DEVICE_PRIVATE' fails as below.

      LD      .tmp_vmlinux.kallsyms1
    mm/gup.o: In function `migrate_device_page':
    /linux/mm/gup.c:1856: undefined reference to `migrate_vma_setup'
    /linux/mm/gup.c:1876: undefined reference to `migrate_vma_pages'
    /linux/mm/gup.c:1879: undefined reference to `migrate_vma_finalize'
    /linux/Makefile:1222: recipe for target 'vmlinux' failed
    make[1]: *** [vmlinux] Error 1

This commit fixes it by implementing an always-failing version of the
function for !CONFIG_DEVICE_PRIVATE'.

[1] https://www.ozlabs.org/~akpm/mmotm/broken-out/mm-gupc-migrate-device-coherent-pages-when-pinning-instead-of-failing.patch

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/gup.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/mm/gup.c b/mm/gup.c
index 1df99a5e90cf..0cf59858114d 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1834,6 +1834,7 @@ struct page *get_dump_page(unsigned long addr)
 #endif /* CONFIG_ELF_CORE */
 
 #ifdef CONFIG_MIGRATION
+#ifdef CONFIG_DEVICE_PRIVATE
 /*
  * Migrates a device coherent page back to normal memory. Caller should have a
  * reference on page which will be copied to the new page if migration is
@@ -1887,6 +1888,14 @@ static struct page *migrate_device_page(struct page *page,
 
 	return dpage;
 }
+#else
+static inline struct page *migrate_device_page(struct page *page,
+					unsigned int gup_flags)
+{
+	return NULL;
+}
+#endif /* CONFIG_DEVICE_PRIVATE */
+
 
 /*
  * Check whether all pages are pinnable, if so return number of pages.  If some
-- 
2.17.1