linux-kernel - Re: [PATCH 2/2] [RFC] arm64: Add dependencies to vendor-specific errata

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Date:   Thu, 16 Apr 2020 17:38:07 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Andy Gross <agross@...nel.org>, Wei Xu <xuwei5@...ilicon.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Robert Richter <rrichter@...vell.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 2/2] [RFC] arm64: Add dependencies to vendor-specific errata

Hi Mark,

On Thu, Apr 16, 2020 at 2:56 PM Mark Rutland <mark.rutland@....com> wrote:
> On Thu, Apr 16, 2020 at 01:56:58PM +0200, Geert Uytterhoeven wrote:
> > Currently the user is asked about enabling support for each and every
> > vendor-specific erratum, even when support for the specific platform is
> > not enabled.
> >
> > Fix this by adding platform dependencies to the config options
> > controlling support for vendor-specific errata.
> >
> > Note that FUJITSU_ERRATUM_010001 is left untouched, as no config symbol
> > exists for the Fujitsu A64FX platform.
> >
> > Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
>
> I'm not su1re that it makes sense to do this in general, becaose the
> ARCH_* platform symbols are about plactform/SoC support (e.g. pinctrl
> drivers), and these are (mostly) CPU-local and/or VM-visible.
>
> I think that it makes sense for those to be independent because:
>
> * future SoCs in the same family might not need the same CPU errata
>   workarounds, and it's arguably just as confusing to have the option
>   there.

True.  But at least the dependency restricts the confusion to a smaller
audience.

> * It prevents building a minimal VM image with all (non-virtualized)
>   platform support disabled, but all possible (VM-visible) errata
>   options enabled. I do that occassionally for testing/analysis, and I
>   can imagine this is useful for those building images that are only
>   intended to be used in VMs.

Oh, you also want to build a "generic" guest kernel, with all ARCH_*
symbols disabled. Let's hope a maleficent user cannot disable errata
mitigations in the guest kernel and break the host ;-)
And perhaps you do want to enable some platform-specific drivers for
VFIO pass-through?  Hence having ARCH_* dependencies on those drivers
means they cannot be enabled :-( Hmm...

> I think the change to SOCIONEXT_SYNQUACER_PREITS makes sense given
> that's a platform-level detail. Arguably that should be moved into
> drivers/irqchip/Kconfig.

OK, makes sense.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds