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From:   John Stultz <john.stultz@linaro.org>
Date:   Fri, 14 Jan 2022 17:17:39 -0800
Message-ID: <CALAqxLUSjHoLpgFLcvqmDfv7Uip2VwHS5d_5x2nzw=P3rA2NDA@mail.gmail.com>
Subject: Re: [PATCH v3] dma-buf: dma-heap: Add a size check for allocation
To:     "Guangming.Cao" <guangming.cao@mediatek.com>
Cc:     =?UTF-8?Q?Christian_K=C3=B6nig?= <christian.koenig@amd.com>,
        "Ruhl, Michael J" <michael.j.ruhl@intel.com>,
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On Fri, Jan 14, 2022 at 4:04 AM Guangming.Cao
<guangming.cao@mediatek.com> wrote:
>
> On Fri, 2022-01-14 at 08:16 +0100, Christian K=C3=B6nig wrote:
> > Am 14.01.22 um 00:26 schrieb John Stultz:
> > > On Thu, Jan 13, 2022 at 5:05 AM Christian K=C3=B6nig
> > > <christian.koenig@amd.com> wrote:
> > > > Am 13.01.22 um 14:00 schrieb Ruhl, Michael J:
> > > > > > -----Original Message-----
> > > > > > From: dri-devel <dri-devel-bounces@lists.freedesktop.org> On
> > > > > > Behalf Of
> > > > > > Ruhl, Michael J
> > > > > > > -----Original Message-----
> > > > > > > From: dri-devel <dri-devel-bounces@lists.freedesktop.org>
> > > > > > > On Behalf Of
> > > > > > > guangming.cao@mediatek.com
> > > > > > > +   /*
> > > > > > > +    * Invalid size check. The "len" should be less than
> > > > > > > totalram.
> > > > > > > +    *
> > > > > > > +    * Without this check, once the invalid size allocation
> > > > > > > runs on a process
> > > > > > > that
> > > > > > > +    * can't be killed by OOM flow(such as "gralloc" on
> > > > > > > Android devices), it
> > > > > > > will
> > > > > > > +    * cause a kernel exception, and to make matters worse,
> > > > > > > we can't find
> > > > > > > who are using
> > > > > > > +    * so many memory with "dma_buf_debug_show" since the
> > > > > > > relevant
> > > > > > > dma-buf hasn't exported.
> > > > > > > +    */
> > > > > > > +   if (len >> PAGE_SHIFT > totalram_pages())
> > > > > >
> > > > > > If your "heap" is from cma, is this still a valid check?
> > > > >
> > > > > And thinking a bit further, if I create a heap from something
> > > > > else (say device memory),
> > > > > you will need to be able to figure out the maximum allowable
> > > > > check for the specific
> > > > > heap.
> > > > >
> > > > > Maybe the heap needs a callback for max size?
> Yes, I agree with this solution.
> If dma-heap framework support this via adding a callback to support it,
> seems it's more clear than adding a limitation in dma-heap framework
> since each heap maybe has different limitation.
> If you prefer adding callback, I can update this patch and add totalram
> limitation to system dma-heap.

If the max value is per-heap, why not enforce that value in the
per-heap allocation function?

Moving the check to the heap alloc to me seems simpler to me than
adding complexity to the infrastructure to add a heap max_size
callback. Is there some other use for the callback that you envision?

thanks
-john