Merge tag 'armsoc-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/arm/arm-soc

[linux-2.6-microblaze.git] / mm / rmap.c

diff --git a/mm/rmap.c b/mm/rmap.c
index 6db729d..eb47780 100644 (file)
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -64,6 +64,7 @@
 #include <linux/backing-dev.h>
 #include <linux/page_idle.h>
 #include <linux/memremap.h>
+#include <linux/userfaultfd_k.h>
 
 #include <asm/tlbflush.h>
 
@@ -1481,11 +1482,16 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
                                set_pte_at(mm, address, pvmw.pte, pteval);
                        }
 
-               } else if (pte_unused(pteval)) {
+               } else if (pte_unused(pteval) && !userfaultfd_armed(vma)) {
                        /*
                         * The guest indicated that the page content is of no
                         * interest anymore. Simply discard the pte, vmscan
                         * will take care of the rest.
+                        * A future reference will then fault in a new zero
+                        * page. When userfaultfd is active, we must not drop
+                        * this page though, as its main user (postcopy
+                        * migration) will not expect userfaults on already
+                        * copied pages.
                         */
                        dec_mm_counter(mm, mm_counter(page));
                        /* We have to invalidate as we cleared the pte */