Fix ZERO_PAGE breakage with vmware

commit 672ca28e300c17bf8d792a2a7a8631193e580c74 upstream

Commit 89f5b7da2a6bad2e84670422ab8192382a5aeb9f ("Reinstate ZERO_PAGE
optimization in 'get_user_pages()' and fix XIP") broke vmware, as
reported by Jeff Chua:

  "This broke vmware 6.0.4.
   Jun 22 14:53:03.845: vmx| NOT_IMPLEMENTED
   /build/mts/release/bora-93057/bora/vmx/main/vmmonPosix.c:774"

and the reason seems to be that there's an old bug in how we handle do
FOLL_ANON on VM_SHARED areas in get_user_pages(), but since it only
triggered if the whole page table was missing, nobody had apparently hit
it before.

The recent changes to 'follow_page()' made the FOLL_ANON logic trigger
not just for whole missing page tables, but for individual pages as
well, and exposed this problem.

This fixes it by making the test for when FOLL_ANON is used more
careful, and also makes the code easier to read and understand by moving
the logic to a separate inline function.

Reported-and-tested-by: Jeff Chua <jeff.chua.linux@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/mm/memory.c b/mm/memory.c
index db6590c8cc11adc70a62e678d14f887b8ad60fda..df84668807ad5a24ff477967fc2f6f471be8ca2b 100644 (file)
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -989,6 +989,26 @@ no_page_table:
        return page;
 }
 
+/* Can we do the FOLL_ANON optimization? */
+static inline int use_zero_page(struct vm_area_struct *vma)
+{
+       /*
+        * We don't want to optimize FOLL_ANON for make_pages_present()
+        * when it tries to page in a VM_LOCKED region. As to VM_SHARED,
+        * we want to get the page from the page tables to make sure
+        * that we serialize and update with any other user of that
+        * mapping.
+        */
+       if (vma->vm_flags & (VM_LOCKED | VM_SHARED))
+               return 0;
+       /*
+        * And if we have a fault or a nopfn routine, it's not an
+        * anonymous region.
+        */
+       return !vma->vm_ops ||
+               (!vma->vm_ops->fault && !vma->vm_ops->nopfn);
+}
+
 int get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
                unsigned long start, int len, int write, int force,
                struct page **pages, struct vm_area_struct **vmas)
@@ -1063,9 +1083,7 @@ int get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
                foll_flags = FOLL_TOUCH;
                if (pages)
                        foll_flags |= FOLL_GET;
-               if (!write && !(vma->vm_flags & VM_LOCKED) &&
-                   (!vma->vm_ops || (!vma->vm_ops->nopage &&
-                                       !vma->vm_ops->fault)))
+               if (!write && use_zero_page(vma))
                        foll_flags |= FOLL_ANON;
 
                do {