linux-kernel - Re: [PATCH] KVM: arm64: Cleanup the __get_fault_info() to take out the code that validates HPFAR

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Date:   Wed, 28 Sep 2022 06:40:03 -0400
From:   Marc Zyngier <maz@...nel.org>
To:     Mingwei Zhang <mizhang@...gle.com>
Cc:     Oliver Upton <oliver.upton@...ux.dev>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "moderated list:KERNEL VIRTUAL MACHINE FOR ARM64 (KVM/arm64)" 
        <kvmarm@...ts.cs.columbia.edu>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] KVM: arm64: Cleanup the __get_fault_info() to take out the code that validates HPFAR

Mingwei,

On Tue, 27 Sep 2022 13:48:52 -0400,
Mingwei Zhang <mizhang@...gle.com> wrote:
> 
> >
> > Honestly, I'd refrain from such changes *unless* they enable something
> > else. The current code is well understood by people hacking on it, and
> > although I don't mind revamping it, it has to be for a good reason.
> >
> > I'd be much more receptive to such a change if it was a prefix to
> > something that actually made a significant change.
> >
> > Thanks,
> >
> >         M.
> >
> Hi Marc,
> 
> Thanks for the feedback.  I am not sure about the style of the KVM ARM
> side. But in general I think mixing the generic code for ARM and
> specific CPU errata handling is misleading. For instance, in this
> case:
> 
> +     if ((esr & ESR_ELx_FSC_TYPE) == FSC_PERM)
> +             return false;
> +
> +     if (cpus_have_final_cap(ARM64_WORKAROUND_834220))
> +             return false;
> 
> As shown it would be much cleaner to separate the two cases as the
> former case is suggested in ARMv8 Spec D13.2.55. The latter case would
> definitely come from a different source.

I think we're talking at cross purposes. I don't object to the change
per se. I simply question its value *in isolation*. One of the many
things that makes the kernel hard to maintain is churn. Refactoring
just for the sake of it *is* churn. In this case, cosmetic churn.

But if you make this is part of something touching this area and
improving things from a functional perspective, then I'll happily
merge it.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.