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    Subject[PATCH 4.2.y-ckt 42/64] arm64: mm: avoid calling apply_to_page_range on empty range
    Date
    4.2.8-ckt4 -stable review patch.  If anyone has any objections, please let me know.

    ---8<------------------------------------------------------------

    From: =?UTF-8?q?Mika=20Penttil=C3=A4?= <mika.penttila@nextfour.com>

    commit 57adec866c0440976c96a4b8f5b59fb411b1cacb upstream.

    Calling apply_to_page_range with an empty range results in a BUG_ON
    from the core code. This can be triggered by trying to load the st_drv
    module with CONFIG_DEBUG_SET_MODULE_RONX enabled:

    kernel BUG at mm/memory.c:1874!
    Internal error: Oops - BUG: 0 [#1] PREEMPT SMP
    Modules linked in:
    CPU: 3 PID: 1764 Comm: insmod Not tainted 4.5.0-rc1+ #2
    Hardware name: ARM Juno development board (r0) (DT)
    task: ffffffc9763b8000 ti: ffffffc975af8000 task.ti: ffffffc975af8000
    PC is at apply_to_page_range+0x2cc/0x2d0
    LR is at change_memory_common+0x80/0x108

    This patch fixes the issue by making change_memory_common (called by the
    set_memory_* functions) a NOP when numpages == 0, therefore avoiding the
    erroneous call to apply_to_page_range and bringing us into line with x86
    and s390.

    Reviewed-by: Laura Abbott <labbott@redhat.com>
    Acked-by: David Rientjes <rientjes@google.com>
    Signed-off-by: Mika Penttilä <mika.penttila@nextfour.com>
    Signed-off-by: Will Deacon <will.deacon@arm.com>
    Signed-off-by: Kamal Mostafa <kamal@canonical.com>
    ---
    arch/arm64/mm/pageattr.c | 3 +++
    1 file changed, 3 insertions(+)

    diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
    index e47ed1c..545710f 100644
    --- a/arch/arm64/mm/pageattr.c
    +++ b/arch/arm64/mm/pageattr.c
    @@ -57,6 +57,9 @@ static int change_memory_common(unsigned long addr, int numpages,
    if (end < MODULES_VADDR || end >= MODULES_END)
    return -EINVAL;

    + if (!numpages)
    + return 0;
    +
    data.set_mask = set_mask;
    data.clear_mask = clear_mask;

    --
    1.9.1
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