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

[Mukesh Ojha]

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@xxxxxxxxxxx>
> > > ---
> > >   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.