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Date:   Tue, 26 Jul 2022 11:00:21 +0100
Message-ID: <87a68wxkga.wl-maz@kernel.org>
From:   Marc Zyngier <maz@kernel.org>
To:     Kalesh Singh <kaleshsingh@google.com>
Cc:     mark.rutland@arm.com, broonie@kernel.org,
        madvenka@linux.microsoft.com, tabba@google.com,
        oliver.upton@linux.dev, will@kernel.org, qperret@google.com,
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        suzuki.poulose@arm.com, catalin.marinas@arm.com,
        andreyknvl@gmail.com, vincenzo.frascino@arm.com,
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        elver@google.com, keirf@google.com, yuzenghui@huawei.com,
        ardb@kernel.org, oupton@google.com,
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        linux-kernel@vger.kernel.org, android-mm@google.com,
        kernel-team@android.com
Subject: Re: [PATCH v6 12/17] KVM: arm64: Add PROTECTED_NVHE_STACKTRACE Kconfig
In-Reply-To: <20220726073750.3219117-13-kaleshsingh@google.com>
References: <20220726073750.3219117-1-kaleshsingh@google.com>
        <20220726073750.3219117-13-kaleshsingh@google.com>
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On Tue, 26 Jul 2022 08:37:45 +0100,
Kalesh Singh <kaleshsingh@google.com> wrote:
>=20
> This can be used to disable stacktrace for the protected KVM
> nVHE hypervisor, in order to save on the associated memory usage.
>=20
> This option is disabled by default, since protected KVM is not widely
> used on platforms other than Android currently.
>=20
> Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
> Reviewed-by: Fuad Tabba <tabba@google.com>
> Tested-by: Fuad Tabba <tabba@google.com>
> ---
>=20
> Changes in v6:
>   - Add Fuad=E2=80=99s Reviewed-by and Tested-by tags
>=20
> Changes in v5:
>   - Make PROTECTED_NVHE_STACKTRACE depend on NVHE_EL2_DEBUG, per Marc
>=20
>  arch/arm64/kvm/Kconfig | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
>=20
> 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
> =20
>  	  If unsure, say N.
> =20
> +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.

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

Thanks,

	M.

--=20
Without deviation from the norm, progress is not possible.