linux-hardening - Re: [REBASE PATCH v5 08/17] arm64: mm: Add dynamic ramoops region support through command line

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Date:   Wed, 13 Sep 2023 11:25:46 +0100
From:   Will Deacon <will@...nel.org>
To:     Mukesh Ojha <quic_mojha@...cinc.com>
Cc:     corbet@....net, agross@...nel.org, andersson@...nel.org,
        konrad.dybcio@...aro.org, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org,
        keescook@...omium.org, tony.luck@...el.com, gpiccoli@...lia.com,
        mathieu.poirier@...aro.org, catalin.marinas@....com,
        linus.walleij@...aro.org, andy.shevchenko@...il.com,
        vigneshr@...com, nm@...com, matthias.bgg@...il.com,
        kgene@...nel.org, alim.akhtar@...sung.com, bmasney@...hat.com,
        quic_tsoni@...cinc.com, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-hardening@...r.kernel.org, linux-remoteproc@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-gpio@...r.kernel.org,
        linux-mediatek@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, kernel@...cinc.com
Subject: Re: [REBASE PATCH v5 08/17] arm64: mm: Add dynamic ramoops region
 support through command line

On Wed, Sep 13, 2023 at 12:32:54PM +0530, Mukesh Ojha wrote:
> Thanks for the response.
> 
> On 9/12/2023 3:48 PM, Will Deacon wrote:
> > On Mon, Sep 11, 2023 at 04:23:50PM +0530, Mukesh Ojha wrote:
> > > The reserved memory region for ramoops is assumed to be at a fixed
> > > and known location when read from the devicetree. This may not be
> > > required for something like Qualcomm's minidump which is interested
> > > in knowing addresses of ramoops region but it does not put hard
> > > requirement of address being fixed as most of it's SoC does not
> > > support warm reset and does not use pstorefs at all instead it has
> > > firmware way of collecting ramoops region if it gets to know the
> > > address and register it with apss minidump table which is sitting
> > > in shared memory region in DDR and firmware will have access to
> > > these table during reset and collects it on crash of SoC.
> > > 
> > > So, add the support of reserving ramoops region to be dynamically
> > > allocated early during boot if it is request through command line
> > > via 'dyn_ramoops_size=' and fill up reserved resource structure and
> > > export the structure, so that it can be read by ramoops driver.
> > > 
> > > Signed-off-by: Mukesh Ojha <quic_mojha@...cinc.com>
> > > ---
> > >   arch/arm64/mm/init.c       | 94 ++++++++++++++++++++++++++++++++++++++++++++++
> > 
> > Why does this need to be in the arch code? There's absolutely nothing
> > arm64-specific here.
> 
> Current clients of this cmdline would be only arm64, and that is the
> reason of putting this here.

I don't think that's a strong enough justification, tbh. We should at
least be able to compile this for other architectures using TEST_COMPILE
and so somewhere under drivers/ makes more sense to me.

Will