[PATCH] mm/device-public-memory: Fix edge case in _vm_normal_page()

From: Reza Arbab
Date: Fri Sep 22 2017 - 10:56:31 EST

With device public pages at the end of my memory space, I'm getting
output from _vm_normal_page():

BUG: Bad page map in process migrate_pages pte:c0800001ffff0d06 pmd:f95d3000
addr:00007fff89330000 vm_flags:00100073 anon_vma:c0000000fa899320 mapping: (null) index:7fff8933
file: (null) fault: (null) mmap: (null) readpage: (null)
CPU: 0 PID: 13963 Comm: migrate_pages Tainted: P B OE 4.14.0-rc1-wip #155
Call Trace:
[c0000000f965f910] [c00000000094d55c] dump_stack+0xb0/0xf4 (unreliable)
[c0000000f965f950] [c0000000002b269c] print_bad_pte+0x28c/0x340
[c0000000f965fa00] [c0000000002b59c0] _vm_normal_page+0xc0/0x140
[c0000000f965fa20] [c0000000002b6e64] zap_pte_range+0x664/0xc10
[c0000000f965fb00] [c0000000002b7858] unmap_page_range+0x318/0x670
[c0000000f965fbd0] [c0000000002b8074] unmap_vmas+0x74/0xe0
[c0000000f965fc20] [c0000000002c4a18] exit_mmap+0xe8/0x1f0
[c0000000f965fce0] [c0000000000ecbdc] mmput+0xac/0x1f0
[c0000000f965fd10] [c0000000000f62e8] do_exit+0x348/0xcd0
[c0000000f965fdd0] [c0000000000f6d2c] do_group_exit+0x5c/0xf0
[c0000000f965fe10] [c0000000000f6ddc] SyS_exit_group+0x1c/0x20
[c0000000f965fe30] [c00000000000b184] system_call+0x58/0x6c

The pfn causing this is the very last one. Correct the bounds check

Fixes: df6ad69838fc ("mm/device-public-memory: device memory cache coherent with CPU")
Cc: JÃrÃme Glisse <jglisse@xxxxxxxxxx>
Signed-off-by: Reza Arbab <arbab@xxxxxxxxxxxxxxxxxx>
mm/memory.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/memory.c b/mm/memory.c
index ec4e154..a728bed 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -845,7 +845,7 @@ struct page *_vm_normal_page(struct vm_area_struct *vma, unsigned long addr,
* vm_normal_page() so that we do not have to special case all
* call site of vm_normal_page().
- if (likely(pfn < highest_memmap_pfn)) {
+ if (likely(pfn <= highest_memmap_pfn)) {
struct page *page = pfn_to_page(pfn);

if (is_device_public_page(page)) {