linux-kernel - Re: [PATCH v6 12/17] KVM: arm64: Add PROTECTED_NVHE

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Date:   Tue, 26 Jul 2022 08:33:20 -0700
From:   Kalesh Singh <kaleshsingh@...gle.com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     Mark Rutland <mark.rutland@....com>,
        Mark Brown <broonie@...nel.org>,
        "Madhavan T. Venkataraman" <madvenka@...ux.microsoft.com>,
        Fuad Tabba <tabba@...gle.com>,
        Oliver Upton <oliver.upton@...ux.dev>,
        Will Deacon <will@...nel.org>,
        Quentin Perret <qperret@...gle.com>,
        James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        andreyknvl@...il.com, vincenzo.frascino@....com,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        Marco Elver <elver@...gle.com>, Keir Fraser <keirf@...gle.com>,
        Zenghui Yu <yuzenghui@...wei.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Oliver Upton <oupton@...gle.com>,
        "moderated list:ARM64 PORT (AARCH64 ARCHITECTURE)" 
        <linux-arm-kernel@...ts.infradead.org>,
        kvmarm <kvmarm@...ts.cs.columbia.edu>,
        LKML <linux-kernel@...r.kernel.org>, android-mm@...gle.com,
        "Cc: Android Kernel" <kernel-team@...roid.com>
Subject: Re: [PATCH v6 12/17] KVM: arm64: Add PROTECTED_NVHE_STACKTRACE Kconfig

On Tue, Jul 26, 2022 at 3:00 AM Marc Zyngier <maz@...nel.org> wrote:
>
> On Tue, 26 Jul 2022 08:37:45 +0100,
> Kalesh Singh <kaleshsingh@...gle.com> wrote:
> >
> > This can be used to disable stacktrace for the protected KVM
> > nVHE hypervisor, in order to save on the associated memory usage.
> >
> > This option is disabled by default, since protected KVM is not widely
> > used on platforms other than Android currently.
> >
> > Signed-off-by: Kalesh Singh <kaleshsingh@...gle.com>
> > Reviewed-by: Fuad Tabba <tabba@...gle.com>
> > Tested-by: Fuad Tabba <tabba@...gle.com>
> > ---
> >
> > Changes in v6:
> >   - Add Fuad’s Reviewed-by and Tested-by tags
> >

> > Changes in v5:
> >   - Make PROTECTED_NVHE_STACKTRACE depend on NVHE_EL2_DEBUG, per Marc
> >
> >  arch/arm64/kvm/Kconfig | 15 +++++++++++++++
> >  1 file changed, 15 insertions(+)
> >
> > diff --git a/arch/arm64/kvm/Kconfig b/arch/arm64/kvm/Kconfig
> > index 8a5fbbf084df..09c995869916 100644
> > --- a/arch/arm64/kvm/Kconfig
> > +++ b/arch/arm64/kvm/Kconfig
> > @@ -46,6 +46,21 @@ menuconfig KVM
> >
> >         If unsure, say N.
> >
> > +config PROTECTED_NVHE_STACKTRACE
> > +     bool "Protected KVM hypervisor stacktraces"
> > +     depends on NVHE_EL2_DEBUG
> > +     default n
> > +     help
> > +       Say Y here to enable pKVM hypervisor stacktraces on hyp_panic()
> > +
> > +       If you are not using protected nVHE (pKVM), say N.
> > +
> > +       If using protected nVHE mode, but cannot afford the associated
> > +       memory cost (less than 0.75 page per CPU) of pKVM stacktraces,
> > +       say N.
> > +
> > +       If unsure, say N.
> > +
> >  config NVHE_EL2_DEBUG
> >       bool "Debug mode for non-VHE EL2 object"
> >       depends on KVM
>
> Having NVHE_EL2_DEBUG after PROTECTED_NVHE_STACKTRACE is pretty odd
> when you use 'make menuconfig', as the new option appears out of
> sequence.

Ahh good catch. Should have moved it when the dependency got changed.

>
> I'll move it around, no need to respin for this.
>

Thanks Marc.


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