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    Subject[125/244] mm: sync vmalloc address space page tables in alloc_vm_area()
    3.0-stable review patch.  If anyone has any objections, please let us know.


    From: David Vrabel <>

    commit 461ae488ecb125b140d7ea29ceeedbcce9327003 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

    (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 ef691947d8a3 ("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 <>
    Cc: Konrad Rzeszutek Wilk <>
    Cc: Ian Campbell <>
    Cc: Keir Fraser <>
    Signed-off-by: Andrew Morton <>
    Signed-off-by: Linus Torvalds <>
    Signed-off-by: Greg Kroah-Hartman <>

    mm/vmalloc.c | 8 ++++++++
    1 file changed, 8 insertions(+)

    --- a/mm/vmalloc.c
    +++ b/mm/vmalloc.c
    @@ -2154,6 +2154,14 @@ struct vm_struct *alloc_vm_area(size_t s
    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;

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      Last update: 2011-09-29 01:05    [W:0.021 / U:18.664 seconds]
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