mm: sync vmalloc address space page tables in alloc_vm_area()
461ae488 · David Vrabel <[email protected]> · 2011-09-14 16:22:02 -07:00
Xen backend drivers (e.g., blkback and netback) would sometimes fail to
map grant pages into the vmalloc address space allocated with
alloc_vm_area(). The GNTTABOP_map_grant_ref would fail because Xen could
not find the page (in the L2 table) containing the PTEs it needed to
update.
(XEN) mm.c:3846:d0 Could not find L1 PTE for address fbb42000
netback and blkback were making the hypercall from a kernel thread where
task->active_mm != &init_mm and alloc_vm_area() was only updating the page
tables for init_mm. The usual method of deferring the update to the page
tables of other processes (i.e., after taking a fault) doesn't work as a
fault cannot occur during the hypercall.
This would work on some systems depending on what else was using vmalloc.
Fix this by reverting ef691947d8a3 ("vmalloc: remove vmalloc_sync_all()
from alloc_vm_area()") and add a comment to explain why it's needed.
Signed-off-by: David Vrabel <[email protected]>
Cc: Jeremy Fitzhardinge <[email protected]>
Cc: Konrad Rzeszutek Wilk <[email protected]>
Cc: Ian Campbell <[email protected]>
Cc: Keir Fraser <[email protected]>
Cc: <[email protected]> [3.0.x]
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
- Commit
- 461ae488ecb125b140d7ea29ceeedbcce9327003
- Parents
- 185efc0f
Changes
1 files changed · +8 −0
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 7ef0903..5016f19 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -2140,6 +2140,14 @@ struct vm_struct *alloc_vm_area(size_t size)
return NULL;
}
+ /*
+ * If the allocated address space is passed to a hypercall
+ * before being used then we cannot rely on a page fault to
+ * trigger an update of the page tables. So sync all the page
+ * tables here.
+ */
+ vmalloc_sync_all();
+
return area;
}
EXPORT_SYMBOL_GPL(alloc_vm_area);