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

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Message-ID: <CAL715W+gJKH+3xgFzUjPs6SAMwZCzkF5NNOTDpa4ov2qZ3r_iA@mail.gmail.com>
Date:   Tue, 27 Sep 2022 10:48:52 -0700
From:   Mingwei Zhang <mizhang@...gle.com>
To:     Marc Zyngier <maz@...nel.org>
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

>
> 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.

But I also don't have a strong opinion pushing this one. So, let me
pull it back then :)