Commit 461ae488 authored by David Vrabel's avatar David Vrabel Committed by Linus Torvalds

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

(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 ef691947 ("vmalloc: remove vmalloc_sync_all()
from alloc_vm_area()") and add a comment to explain why it's needed.
Signed-off-by: default avatarDavid Vrabel <>
Cc: Jeremy Fitzhardinge <>
Cc: Konrad Rzeszutek Wilk <>
Cc: Ian Campbell <>
Cc: Keir Fraser <>
Cc: <>		[3.0.x]
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 185efc0f
......@@ -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.
return area;
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