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Date:   Mon, 10 Jul 2023 22:37:10 +0200
From:   Stephan Gerhold <stephan@gerhold.net>
To:     Bjorn Andersson <andersson@kernel.org>,
        Caleb Connolly <caleb.connolly@linaro.org>
Cc:     Andy Gross <agross@kernel.org>,
        Konrad Dybcio <konrad.dybcio@linaro.org>,
        Mathieu Poirier <mathieu.poirier@linaro.org>,
        linux-arm-msm@vger.kernel.org, linux-remoteproc@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 1/2] remoteproc: qcom: Handle reserved-memory
 allocation issues
Message-ID: <ZKxr6hyqq3s7nqix@gerhold.net>
References: <20230529-rproc-of-rmem-v2-0-95e39b959585@gerhold.net>
 <20230529-rproc-of-rmem-v2-1-95e39b959585@gerhold.net>
 <c3f59fb4-4dd8-f27a-d3f5-b1870006a75c@linaro.org>
 <ZIsld-MAdkKvdzTx@gerhold.net>
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On Thu, Jun 15, 2023 at 04:51:44PM +0200, Stephan Gerhold wrote:
> On Thu, Jun 15, 2023 at 11:44:06AM +0100, Caleb Connolly wrote:
> > On 6/14/23 17:31, Stephan Gerhold wrote:
> > > If Linux fails to allocate the dynamic reserved memory specified in the
> > > device tree, the size of the reserved_mem will be 0. Add a check for
> > > this to avoid using an invalid reservation.
> > > 
> > > Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
> > 
> > Other uses of of_reserved_mem_lookup() also have unchecked uses of rmem [1],
> > or check different things [2].
> > 
> > Does it make sense to put this check in the function itself?
> > 
> > I can't think of any obvious scenarios where it makes sense to differentiate
> > between rmem being NULL vs having a size of zero at the time where a driver
> > is fetching it.
> > 
> > As Bjorn described in the rmtfs patch, the memory allocation is essentially
> > ignored, wouldn't it be better to print an error and invalidate the rmem in
> > [3]?
> > 
> 
> "Invalidating" isn't that easy because the reserved_mem is currently
> stored in a simple array. Removing an entry would require shifting all
> following values. But I suppose it would be easy to add the rmem->size
> != 0 check in of_reserved_mem_lookup() so it doesn't have to be checked
> on all usages.
> 
> Given that no one seems to check for this at the moment I'm inclined to
> agree with you that it would be better to handle this directly in
> of_reserved_mem. Bjorn, what do you think?
> 

I sent a v3 with the additional checks reverted. I'll work on a separate
patch series to improve this independently of this one for all users
(directly in of_reserved_mem).

Thanks,
Stephan