2 files changed, 12 insertions, 2 deletions

diff --git a/mm/memory.c b/mm/memory.c
index 9144fae9a68b..b8f97b8575b7 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3299,7 +3299,12 @@ int make_pages_present(unsigned long addr, unsigned long end)
         vma = find_vma(current->mm, addr);
         if (!vma)
                 return -ENOMEM;
-        write = (vma->vm_flags & VM_WRITE) != 0;
+        /*
+         * We want to touch writable mappings with a write fault in order
+         * to break COW, except for shared mappings because these don't COW
+         * and we would not want to dirty them for nothing.
+         */
+        write = (vma->vm_flags & (VM_WRITE | VM_SHARED)) == VM_WRITE;
         BUG_ON(addr >= end);
         BUG_ON(end > vma->vm_end);
         len = DIV_ROUND_UP(end, PAGE_SIZE) - addr/PAGE_SIZE;
diff --git a/mm/mlock.c b/mm/mlock.c
index b70919ce4f72..4f318642fbbe 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -171,7 +171,12 @@ static long __mlock_vma_pages_range(struct vm_area_struct *vma,
         VM_BUG_ON(!rwsem_is_locked(&mm->mmap_sem));
 
         gup_flags = FOLL_TOUCH | FOLL_GET;
-        if (vma->vm_flags & VM_WRITE)
+        /*
+         * We want to touch writable mappings with a write fault in order
+         * to break COW, except for shared mappings because these don't COW
+         * and we would not want to dirty them for nothing.
+         */
+        if ((vma->vm_flags & (VM_WRITE | VM_SHARED)) == VM_WRITE)
                 gup_flags |= FOLL_WRITE;
 
         /* We don't try to access the guard page of a stack vma */