From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Vrabel Subject: [PATCH] mm: sync vmalloc address space page tables in alloc_vm_area() Date: Thu, 1 Sep 2011 12:51:03 +0100 Message-ID: <1314877863-21977-1-git-send-email-david.vrabel@citrix.com> Mime-Version: 1.0 Content-Type: text/plain Return-path: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: xen-devel@lists.xensource.com Cc: Jeremy Fitzhardinge , David Vrabel , Konrad Rzeszutek Wilk List-Id: xen-devel@lists.xenproject.org From: David Vrabel 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 ef691947d8a3d479e67652312783aedcf629320a (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 --- mm/vmalloc.c | 8 ++++++++ 1 files changed, 8 insertions(+), 0 deletions(-) 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); -- 1.7.2.5