mm: thp: relocate flush_cache_range() in migrate_misplaced_transhuge_page()

mainline inclusion
from mainline-4.20-rc1
commit 7eef5f97
category: bugfix
bugzilla: 34611
CVE: NA

-------------------------------------------------
There should be no cache left by the time we overwrite the old transhuge
pmd with the new one.  It's already too late to flush through the virtual
address because we already copied the page data to the new physical
address.

So flush the cache before the data copy.

Also delete the "end" variable to shutoff a "unused variable" warning on
x86 where flush_cache_range() is a noop.

Link: http://lkml.kernel.org/r/20181015202311.7209-1-aarcange@redhat.comSigned-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Acked-by: NKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Aaron Tomlin <atomlin@redhat.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
(cherry picked from commit 7eef5f97)
Signed-off-by: NKefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: NLiu Shixin <liushixin2@huawei.com>
Reviewed-by: NKefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

mm/migrate.c

@@ -2027,7 +2027,6 @@ int migrate_misplaced_transhuge_page(struct mm_struct *mm,
 	struct page *new_page = NULL;
 	int page_lru = page_is_file_cache(page);
 	unsigned long start = address & HPAGE_PMD_MASK;
-	unsigned long end = start + HPAGE_PMD_SIZE;
 
 	new_page = alloc_pages_node(node,
 		(GFP_TRANSHUGE_LIGHT | __GFP_THISNODE),
@@ -2050,6 +2049,8 @@ int migrate_misplaced_transhuge_page(struct mm_struct *mm,
 	/* anon mapping, we can simply copy page->mapping to the new page: */
 	new_page->mapping = page->mapping;
 	new_page->index = page->index;
+	/* flush the cache before copying using the kernel virtual address */
+	flush_cache_range(vma, start, start + HPAGE_PMD_SIZE);
 	migrate_page_copy(new_page, page);
 	WARN_ON(PageLRU(new_page));
 
@@ -2087,7 +2088,6 @@ int migrate_misplaced_transhuge_page(struct mm_struct *mm,
 	 * new page and page_add_new_anon_rmap guarantee the copy is
 	 * visible before the pagetable update.
 	 */
-	flush_cache_range(vma, start, end);
 	page_add_anon_rmap(new_page, vma, start, true);
 	/*
 	 * At this point the pmd is numa/protnone (i.e. non present) and the TLB