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Date:   Fri, 26 May 2023 15:59:07 +0100
From:   Conor Dooley <conor@kernel.org>
To:     Alexandre Ghiti <alexghiti@rivosinc.com>
Cc:     =?iso-8859-1?Q?Bj=F6rn_T=F6pel?= <bjorn@rivosinc.com>,
        Atish Patra <atishp@atishpatra.org>,
        Conor Dooley <conor.dooley@microchip.com>,
        Anup Patel <anup@brainfault.org>,
        Anup Patel <apatel@ventanamicro.com>,
        Alexandre Ghiti <alex@ghiti.fr>, robh@kernel.org,
        jeeheng.sia@starfivetech.com, linux-kernel@vger.kernel.org,
        palmer@rivosinc.com, leyfoon.tan@starfivetech.com,
        mason.huo@starfivetech.com, Guo Ren <guoren@kernel.org>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Song Shuai <suagrfillet@gmail.com>,
        linux-riscv@lists.infradead.org,
        Andrew Jones <ajones@ventanamicro.com>
Subject: Re: Bug report: kernel paniced when system hibernates
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On Fri, May 26, 2023 at 03:14:33PM +0200, Alexandre Ghiti wrote:
> Hi everyone,
>=20
> On Thu, May 25, 2023 at 11:24=E2=80=AFPM Conor Dooley <conor@kernel.org> =
wrote:
> >
> > On Thu, May 25, 2023 at 01:06:04PM -0700, Atish Patra wrote:
> > > On Thu, May 25, 2023 at 11:39=E2=80=AFAM Conor Dooley <conor@kernel.o=
rg> wrote:
> > > >
> > > > On Thu, May 25, 2023 at 11:37:40AM -0700, Atish Patra wrote:
> > > >
> > > > > Any testing of hibernation still needs to revert the patch until =
we
> > > > > have the proper fix.
> > > >
> > > > "the patch" is what exactly? I assume you don't mean depending on
> > > > NONPORTABLE, since that is a Kconfig option.
> > >
> > > Nope. Sorry I meant the commit
> > >
> > > 3335068 ("riscv: Use PUD/P4D/PGD pages for the linear mapping")
> >
> > Ah, if your SBI implementation is one of the affected ones, yeah.
> > If not, you can just set NONPORTABLE :)
>=20
> @Bj=C3=B6rn T=C3=B6pel emitted the idea of excluding from the hibernation=
 all
> the memory nodes in the "/reserved-memory" node
> (https://elixir.bootlin.com/linux/v6.4-rc1/source/Documentation/devicetre=
e/bindings/reserved-memory/reserved-memory.yaml):
> I have to admit that I don't see why it is not done by default by the
> kernel.

My understanding was that it was perfectly fine to use reserved memory
nodes to fence off some memory to use in device drivers etc, which then
may need to be saved/restored.

> Unless there is stuff in this node that needs to be "hibernated", I
> think that would be a very good solution since we would not rely on
> the name of the "internal" nodes of "/reserved-memory" (i.e.
> "mmode_resv").
>=20
> I'm digging into why it is not done by default, just wanted to have
> your feedback before the week-end :)

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