On 01/09/11 22:17, Andrew Morton wrote: > On Thu, 01 Sep 2011 13:37:46 -0700 > Jeremy Fitzhardinge <jeremy@xxxxxxxx> wrote: > >> On 09/01/2011 09:11 AM, Konrad Rzeszutek Wilk wrote: >>> On Thu, Sep 01, 2011 at 12:51:03PM +0100, David Vrabel wrote: >>>> From: David Vrabel <david.vrabel@xxxxxxxxxx> >>> Andrew, >>> >>> I was wondering if you would be Ok with this patch for 3.1. >>> >>> It is a revert (I can prepare a proper revert if you would like >>> that instead of this patch). > > David's patch looks better than a straight reversion. > > Problem is, I can't find David's original email anywhere. Someone's > been playing games with To: headers? Sorry, I should have Cc'd linux-kernel and others on the original patch. >From 6844ca07140e08f29454ca7b3fa459571c7ba428 Mon Sep 17 00:00:00 2001 From: David Vrabel <david.vrabel@xxxxxxxxxx> Date: Thu, 1 Sep 2011 11:42:50 +0100 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 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 <david.vrabel@xxxxxxxxxx> Cc: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx> --- 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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>