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

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Message-ID: <CAJF2gTTXT1UusfCDrccqd1X=16Z2Gg9+cvvhSjohF+D_ukVEiw@mail.gmail.com>
Date:   Fri, 10 Jun 2022 09:12:27 +0800
From:   Guo Ren <guoren@...nel.org>
To:     Heiko Stübner <heiko@...ech.de>
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

On Thu, Jun 9, 2022 at 5:58 PM Heiko Stübner <heiko@...ech.de> wrote:
>
> 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?
+       if (stage != RISCV_ALTERNATIVES_MODULE &&
+           cpu_apply_errata != cpu_req_errata)
                warn_miss_errata(cpu_req_errata - cpu_apply_errata);
+       else if (cpu_apply_errata &= ~cpu_req_errata)
                warn_miss_errata(cpu_req_errata - cpu_apply_errata);

All module's errata should be a subset of the main kernel. Not just
skip the check of MODULE.

>
>
> > 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
> > >
> >
> >
> >
>
>
>
>


-- 
Best Regards
 Guo Ren

ML: https://lore.kernel.org/linux-csky/