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References: <20220721055728.718573-1-kaleshsingh@google.com> <20220721055728.718573-9-kaleshsingh@google.com>
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From:   Fuad Tabba <tabba@google.com>
Date:   Thu, 21 Jul 2022 10:57:44 +0100
Message-ID: <CA+EHjTxtwjf3dMhrBFa0iTMPayV0V0dM-z_Gk_hSQn_hr4zYow@mail.gmail.com>
Subject: Re: [PATCH v5 08/17] KVM: arm64: Add PROTECTED_NVHE_STACKTRACE Kconfig
To:     Kalesh Singh <kaleshsingh@google.com>
Cc:     maz@kernel.org, mark.rutland@arm.com, broonie@kernel.org,
        madvenka@linux.microsoft.com, will@kernel.org, qperret@google.com,
        james.morse@arm.com, alexandru.elisei@arm.com,
        suzuki.poulose@arm.com, catalin.marinas@arm.com,
        andreyknvl@gmail.com, vincenzo.frascino@arm.com,
        mhiramat@kernel.org, ast@kernel.org, wangkefeng.wang@huawei.com,
        elver@google.com, keirf@google.com, yuzenghui@huawei.com,
        ardb@kernel.org, oupton@google.com,
        linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu,
        linux-kernel@vger.kernel.org, kernel-team@android.com
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Hi Kalesh,

On Thu, Jul 21, 2022 at 6:57 AM Kalesh Singh <kaleshsingh@google.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@google.com>
> ---

Just wanted to point out that I have specifically tested this as well,
enabling PROTECTED_NVHE_STACKTRACE but not NVHE_EL2_DEBUG. Works as
expected.

Tested-by: Fuad Tabba <tabba@google.com>
Reviewed-by: Fuad Tabba <tabba@google.com>

Cheers,
/fuad


>
> 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
> --
> 2.37.0.170.g444d1eabd0-goog
>