X-Git-Url: https://git.proxmox.com/?a=blobdiff_plain;f=mm%2Frmap.c;h=83f8705739a23cca9fdf7bb2d2f26d6b03d31156;hb=e04ef105aa64a1c667712d65d18ac69b5612b712;hp=47db27f8049e105b88f1ed60054b1576b8056dac;hpb=51090c5d6de08cfc86b2d861775dedddd9a2c023;p=mirror_ubuntu-bionic-kernel.git

diff --git a/mm/rmap.c b/mm/rmap.c
index 47db27f8049e..83f8705739a2 100644
--- 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>
 
@@ -1483,11 +1484,16 @@ 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 */