linux-kernel - Re: [PATCH v4 08/18] KVM: arm64: Add PROTECTED_NVHE

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Date:   Mon, 18 Jul 2022 07:55:44 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Kalesh Singh <kaleshsingh@...gle.com>
Cc:     mark.rutland@....com, broonie@...nel.org,
        madvenka@...ux.microsoft.com, will@...nel.org, qperret@...gle.com,
        tabba@...gle.com, james.morse@....com, alexandru.elisei@....com,
        suzuki.poulose@....com, catalin.marinas@....com,
        andreyknvl@...il.com, russell.king@...cle.com,
        vincenzo.frascino@....com, mhiramat@...nel.org, ast@...nel.org,
        wangkefeng.wang@...wei.com, elver@...gle.com, keirf@...gle.com,
        yuzenghui@...wei.com, ardb@...nel.org, oupton@...gle.com,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-kernel@...r.kernel.org, kernel-team@...roid.com
Subject: Re: [PATCH v4 08/18] KVM: arm64: Add PROTECTED_NVHE_STACKTRACE Kconfig

[- Drew and android-mm, as both addresses bounce]

On Fri, 15 Jul 2022 07:10:17 +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>
> ---
>  arch/arm64/kvm/Kconfig | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
> 
> diff --git a/arch/arm64/kvm/Kconfig b/arch/arm64/kvm/Kconfig
> index 8a5fbbf084df..1edab6f8a3b8 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 KVM
> +	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.
> +

Can we make this depend on NVHE_EL2_DEBUG instead? I'd like to keep
the disclosing of EL2 information in protected mode a strict debug
feature.

>  config NVHE_EL2_DEBUG
>  	bool "Debug mode for non-VHE EL2 object"
>  	depends on KVM

Thanks,

	M.

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