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

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Message-ID: <3273977a-be7d-85f6-6754-52a3dd9b784a@quicinc.com>
Date:   Thu, 5 Oct 2023 16:52:20 +0530
From:   Mukesh Ojha <quic_mojha@...cinc.com>
To:     Kees Cook <keescook@...omium.org>, Will Deacon <will@...nel.org>
CC:     <corbet@....net>, <agross@...nel.org>, <andersson@...nel.org>,
        <konrad.dybcio@...aro.org>, <robh+dt@...nel.org>,
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Subject: Re: [REBASE PATCH v5 08/17] arm64: mm: Add dynamic ramoops region
 support through command line

Sorry for the late reply, was on a long vacation.

On 9/14/2023 4:47 AM, Kees Cook wrote:
> On Tue, Sep 12, 2023 at 11:18:20AM +0100, 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.
> 
> I would agree: this needs to be in ramoops itself, IMO. It should be a
> ramoops module argument, too.
> 
> It being unhelpful for systems that don't have an external consumer is
> certainly true, but I think it would still make more sense for this
> change to live entirely within ramoops. Specifically: you're
> implementing a pstore backend behavioral change. In the same way that
> patch 10 is putting the "output" side of this into pstore/, I'd expect
> the "input" side also in pstore/

How do we reserve memory? are you suggesting to use dma api's for
dynamic ramoops ?

-Mukesh
> 
> More comments there, though.
>