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mm: sync vmalloc address space page tables in alloc_vm_area()

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commit 461ae488ec upstream.

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 ef691947d8 ("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@citrix.com>
Cc: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Ian Campbell <Ian.Campbell@citrix.com>
Cc: Keir Fraser <keir.xen@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

(cherry picked from commit d63c8a029e509ad48ee9290874731789f9008537)
This commit is contained in:
David Vrabel 2011-09-14 16:22:02 -07:00 committed by Stephen Boyd
parent 6e206b79df
commit d2affbaaa2
1 changed files with 8 additions and 0 deletions
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8
mm/vmalloc.c
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@ -2259,6 +2259,14 @@ struct vm_struct *alloc_vm_area(size_t size, pte_t **ptes)
return NULL; 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; return area;
} }
EXPORT_SYMBOL_GPL(alloc_vm_area); EXPORT_SYMBOL_GPL(alloc_vm_area);