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From:   Atish Patra <atishp@atishpatra.org>
Date:   Fri, 26 May 2023 11:48:27 -0700
Message-ID: <CAOnJCU+2PHToCSWdauh5CarUa8iNcE4Ugv3gj=TiLVVoevU_iQ@mail.gmail.com>
Subject: Re: Bug report: kernel paniced when system hibernates
To:     Alexandre Ghiti <alexghiti@rivosinc.com>
Cc:     Anup Patel <anup@brainfault.org>, Alexandre Ghiti <alex@ghiti.fr>,
        Conor Dooley <conor@kernel.org>,
        =?UTF-8?B?QmrDtnJuIFTDtnBlbA==?= <bjorn@rivosinc.com>,
        Conor Dooley <conor.dooley@microchip.com>,
        Anup Patel <apatel@ventanamicro.com>, 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>
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On Fri, May 26, 2023 at 8:22=E2=80=AFAM Alexandre Ghiti <alexghiti@rivosinc=
.com> wrote:
>
> On Fri, May 26, 2023 at 5:17=E2=80=AFPM Anup Patel <anup@brainfault.org> =
wrote:
> >
> > On Fri, May 26, 2023 at 8:42=E2=80=AFPM Alexandre Ghiti <alex@ghiti.fr>=
 wrote:
> > >
> > >
> > > On 26/05/2023 16:59, Conor Dooley wrote:
> > > > On Fri, May 26, 2023 at 03:14:33PM +0200, Alexandre Ghiti wrote:
> > > >> Hi everyone,
> > > >>
> > > >> On Thu, May 25, 2023 at 11:24=E2=80=AFPM Conor Dooley <conor@kerne=
l.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@ker=
nel.org> wrote:
> > > >>>>> On Thu, May 25, 2023 at 11:37:40AM -0700, Atish Patra wrote:
> > > >>>>>
> > > >>>>>> Any testing of hibernation still needs to revert the patch unt=
il 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 :)
> > > >> @Bj=C3=B6rn T=C3=B6pel emitted the idea of excluding from the hibe=
rnation all
> > > >> the memory nodes in the "/reserved-memory" node
> > > >> (https://elixir.bootlin.com/linux/v6.4-rc1/source/Documentation/de=
vicetree/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 mem=
ory
> > > > nodes to fence off some memory to use in device drivers etc, which =
then
> > > > may need to be saved/restored.
> > >
> > >
> > > Agreed, but I would say that it's up to the driver then to take care =
of
> > > that, see https://docs.kernel.org/driver-api/pm/notifiers.html
> >
> > I agree, it should be drivers responsibility to save/restore the dedica=
ted
> > reserved memory used by itself.
> >
> > Although, I think we should at least save/restore reserved memory
> > regions having "reusable" property set.
>

That would be certainly ideal. However, that piece of code has been
present for ages (last commit was in 2008!).
There may be a bunch of drivers written with this builtin assumption.

> Good point! I'll propose an RFC and gather feedback from the people in
> charge of the hibernation process.

Hopefully, it's not too bad.

>
> >
> > Regards,
> > Anup
> >
> > >
> > >
> > > >> 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 o=
n
> > > >> the name of the "internal" nodes of "/reserved-memory" (i.e.
> > > >> "mmode_resv").
> > > >>
> > > >> I'm digging into why it is not done by default, just wanted to hav=
e
> > > >> your feedback before the week-end :)


--=20
Regards,
Atish