Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Wed, 28 Sep 2022 06:40:03 -0400
Message-ID: <86pmff7pfg.wl-maz@kernel.org>
From:   Marc Zyngier <maz@kernel.org>
To:     Mingwei Zhang <mizhang@google.com>
Cc:     Oliver Upton <oliver.upton@linux.dev>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        James Morse <james.morse@arm.com>,
        Alexandru Elisei <alexandru.elisei@arm.com>,
        Suzuki K Poulose <suzuki.poulose@arm.com>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        "moderated list:KERNEL VIRTUAL MACHINE FOR ARM64 (KVM/arm64)" 
        <kvmarm@lists.cs.columbia.edu>, LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] KVM: arm64: Cleanup the __get_fault_info() to take out the code that validates HPFAR
In-Reply-To: <CAL715W+gJKH+3xgFzUjPs6SAMwZCzkF5NNOTDpa4ov2qZ3r_iA@mail.gmail.com>
References: <20220927002715.2142353-1-mizhang@google.com>
        <YzKGqLzjv0I/gkMi@google.com>
        <86zgel6rz8.wl-maz@kernel.org>
        <CAL715W+gJKH+3xgFzUjPs6SAMwZCzkF5NNOTDpa4ov2qZ3r_iA@mail.gmail.com>
User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue)
 FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/27.1
 (aarch64-unknown-linux-gnu) MULE/6.0 (HANACHIRUSATO)
MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue")
Content-Type: text/plain; charset=US-ASCII
Precedence: bulk

Mingwei,

On Tue, 27 Sep 2022 13:48:52 -0400,
Mingwei Zhang <mizhang@google.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.