linux-kernel - Re: [PATCH] riscv: don't warn for sifive erratas in modules

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Date:   Thu, 09 Jun 2022 11:58:40 +0200
From:   Heiko Stübner <heiko@...ech.de>
To:     Guo Ren <guoren@...nel.org>
Cc:     Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Wei Fu <wefu@...hat.com>,
        Christoph Muellner <cmuellner@...ux.com>,
        Philipp Tomsich <philipp.tomsich@...ll.eu>,
        Christoph Hellwig <hch@....de>, Ron Economos <re@...z.net>
Subject: Re: [PATCH] riscv: don't warn for sifive erratas in modules

Hi Guo,

Am Donnerstag, 9. Juni 2022, 03:39:24 CEST schrieb Guo Ren:
> On Wed, Jun 8, 2022 at 8:09 PM Heiko Stuebner <heiko@...ech.de> wrote:
> >
> > The SiFive errata code contains code checking applicable erratas
> > vs. actually applied erratas to suggest missing erratas to the
> > user when their Kconfig options are not enabled.
> >
> > In the main kernel image one can be quite sure that all available
> > erratas appear at least once, so that check will succeed.
> > On the other hand modules can very well not use any errata-relevant
> > code, so the newly added module-alternative support may also patch
> > the module code, but not touch SiFive-specific erratas at all.
> >
> > So to restore the original behaviour don't warn when patching
> > modules. This will keep the warning if necessary for the main kernel
> > image but prevent spurious warnings for modules.
> >
> > Of course having such a vendor-specific warning may not be needed at
> > all, as CONFIG_ERRATA_SIFIVE is selected by CONFIG_SOC_SIFIVE and the
> > individual erratas are default-y so disabling them requires
> > deliberate action anyway. But for now just restore the old behaviour.
> >
> > Fixes: a8e910168bba ("riscv: implement module alternatives")
> > Reported-by: Ron Economos <re@...z.net>
> > Signed-off-by: Heiko Stuebner <heiko@...ech.de>
> > ---
> >  arch/riscv/errata/sifive/errata.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/riscv/errata/sifive/errata.c b/arch/riscv/errata/sifive/errata.c
> > index 672f02b21ce0..1031038423e7 100644
> > --- a/arch/riscv/errata/sifive/errata.c
> > +++ b/arch/riscv/errata/sifive/errata.c
> > @@ -111,6 +111,7 @@ void __init_or_module sifive_errata_patch_func(struct alt_entry *begin,
> >                         cpu_apply_errata |= tmp;
> >                 }
> >         }
> > -       if (cpu_apply_errata != cpu_req_errata)
> > +       if (stage != RISCV_ALTERNATIVES_MODULE &&
> > +           cpu_apply_errata != cpu_req_errata)
> if (cpu_apply_errata &= ~cpu_req_errata)

Hmm, I don't see what that changes?


> Shall we still guarantee the module's must be a subset of the main kernel.'s?

The warning generated there is mainly to warn about some Kconfig options
not being enabled and in individual modules even no errata usage may be
required.


The intent for the patch is to restore how things behaved before
module-alternatives were introduced, so I don't really want to
introduce functional changes ;-) .

But also in the future we could debate if that warning is helpful at all,
as the erratas are enabled automatically by CONFIG_SOC_SIFIVE and
thus disabling individual erratas requires someone to turn them off
manually in their .config .


Heiko

> >                 warn_miss_errata(cpu_req_errata - cpu_apply_errata);
> >  }
> > --
> > 2.35.1
> >
> 
> 
>