Fix ZERO_PAGE breakage with vmware
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>
diff --git a/mm/memory.c b/mm/memory.c
index 9aefaae..423e0e7 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1045,6 +1045,26 @@
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)
@@ -1119,8 +1139,7 @@
foll_flags = FOLL_TOUCH;
if (pages)
foll_flags |= FOLL_GET;
- if (!write && !(vma->vm_flags & VM_LOCKED) &&
- (!vma->vm_ops || !vma->vm_ops->fault))
+ if (!write && use_zero_page(vma))
foll_flags |= FOLL_ANON;
do {