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From:   Alexandre Ghiti <alexghiti@rivosinc.com>
Date:   Fri, 26 May 2023 17:22:47 +0200
Message-ID: <CAHVXubj2oHJGwbfEukxRg58xHyVOieTdCa5wjHsR5XZ8rmxjgg@mail.gmail.com>
Subject: Re: Bug report: kernel paniced when system hibernates
To:     Anup Patel <anup@brainfault.org>
Cc:     Alexandre Ghiti <alex@ghiti.fr>, Conor Dooley <conor@kernel.org>,
        =?UTF-8?B?QmrDtnJuIFTDtnBlbA==?= <bjorn@rivosinc.com>,
        Atish Patra <atishp@atishpatra.org>,
        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 5:17=E2=80=AFPM Anup Patel <anup@brainfault.org> wr=
ote:
>
> On Fri, May 26, 2023 at 8:42=E2=80=AFPM Alexandre Ghiti <alex@ghiti.fr> w=
rote:
> >
> >
> > 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@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@kerne=
l.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 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 :)
> > >> @Bj=C3=B6rn T=C3=B6pel emitted the idea of excluding from the hibern=
ation all
> > >> the memory nodes in the "/reserved-memory" node
> > >> (https://elixir.bootlin.com/linux/v6.4-rc1/source/Documentation/devi=
cetree/bindings/reserved-memory/reserved-memory.yaml):
> > >> I have to admit that I don't see why it is not done by default by th=
e
> > >> kernel.
> > > My understanding was that it was perfectly fine to use reserved memor=
y
> > > nodes to fence off some memory to use in device drivers etc, which th=
en
> > > 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 dedicate=
d
> reserved memory used by itself.
>
> Although, I think we should at least save/restore reserved memory
> regions having "reusable" property set.

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

>
> 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 on
> > >> 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 have
> > >> your feedback before the week-end :)