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    SubjectRe: [PATCH v7 2/2] ARM: ftrace: Add MODULE_PLTS support
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    On 3/12/21 9:24 AM, Qais Yousef wrote:
    > Hi Alexander
    >
    > On 03/10/21 18:17, Alexander Sverdlin wrote:
    >> Hi!
    >>
    >> On 10/03/2021 17:14, Florian Fainelli wrote:
    >>>>>>> I tried on 5.12-rc2 and 5.11 but couldn't reproduce the problem using your
    >>>>> I still can't reproduce on 5.12-rc2.
    >>>>>
    >>>>> I do have CONFIG_ARM_MODULE_PLTS=y. Do you need to do something else after
    >>>>> loading the module? I tried starting ftrace, but maybe there's a particular
    >>>>> combination required?
    >>>> You need to load a BIG module, so big that it has no place in the modules area
    >>>> any more and goes to vmalloc area.
    >>> You absolutely need a very big module maybe more than one. When I tested
    >>> this, I could use the two proprietary modules (*sigh*) that I needed to
    >>> exercise against and loading one but not the other was not enough to
    >>> make the second module loading spill into vmalloc space.
    >>
    >> Here is what I use instead of these real world "proprietary" modules (which of course
    >> were the real trigger for the patch):
    >>
    >> https://www.spinics.net/lists/arm-kernel/msg878599.html
    >
    > I am testing with your module. I can't reproduce the problem you describe with
    > it as I stated.
    >
    > I will try to spend more time on it on the weekend.

    Alexander, do you load one or multiple instances of that fat module?

    The test module does a 6 * 1024 * 1024 / 2 = 3 million repetitions of
    the "nop" instruction which should be 32-bits wide in ARM mode and
    16-bits wide in Thumb mode, right?

    In ARM mode we have a 14MB module space, so 3 * 1024 * 1024 * 4 = 12MB,
    which should still fit within if you have no module loaded, however a
    second instance of the module should make us spill into vmalloc space.

    In Thumb mode, we have a 6MB module space, so 3 * 1024 * 1024 * 2 = 6MB
    so we may spill, but maybe not.

    I was not able to reproduce the warning with just one module, but with
    two (cannot have the same name BTW), it kicked in.
    --
    Florian

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