From 461ae488ecb125b140d7ea29ceeedbcce9327003 Mon Sep 17 00:00:00 2001 From: David Vrabel Date: Wed, 14 Sep 2011 16:22:02 -0700 Subject: [PATCH] mm: sync vmalloc address space page tables in alloc_vm_area() 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 Cc: Jeremy Fitzhardinge Cc: Konrad Rzeszutek Wilk Cc: Ian Campbell Cc: Keir Fraser Cc: [3.0.x] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/vmalloc.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/mm/vmalloc.c b/mm/vmalloc.c index 7ef0903058ee..5016f19e1661 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);