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). The users of this particular function (alloc_vm_area) are just Xen. There are no others. > > 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>