[PATCH] mm: fix pfn_t to page conversion in vm_insert_mixed

From: Dan Williams
Date: Tue Jan 26 2016 - 13:39:13 EST

pfn_t_to_page() honors the flags in the pfn_t value to determine if a
pfn is backed by a page. However, vm_insert_mixed() was originally
written to use pfn_valid() to make this determination. To restore the
old/correct behavior, ignore the pfn_t flags in the !pfn_t_devmap() case
and fallback to trusting pfn_valid().

Fixes: 01c8f1c44b83 ("mm, dax, gpu: convert vm_insert_mixed to pfn_t")
Cc: Dave Hansen <dave@xxxxxxxx>
Cc: David Airlie <airlied@xxxxxxxx>
Reported-by: Julian Margetson <runaway@xxxxxxxx>
Reported-by: Tomi Valkeinen <tomi.valkeinen@xxxxxx>
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
mm/memory.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index 30991f83d0bf..93ce37989471 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1591,10 +1591,15 @@ int vm_insert_mixed(struct vm_area_struct *vma, unsigned long addr,
* than insert_pfn). If a zero_pfn were inserted into a VM_MIXEDMAP
* without pte special, it would there be refcounted as a normal page.
- if (!HAVE_PTE_SPECIAL && pfn_t_valid(pfn)) {
+ if (!HAVE_PTE_SPECIAL && !pfn_t_devmap(pfn) && pfn_t_valid(pfn)) {
struct page *page;

- page = pfn_t_to_page(pfn);
+ /*
+ * At this point we are committed to insert_page()
+ * regardless of whether the caller specified flags that
+ * result in pfn_t_has_page() == false.
+ */
+ page = pfn_to_page(pfn_t_to_pfn(pfn));
return insert_page(vma, addr, page, vma->vm_page_prot);
return insert_pfn(vma, addr, pfn, vma->vm_page_prot);