netdev - Re: [PATCH v14 09/10] doc: add ptp_kvm introduction for arm64 support

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Date:   Fri, 04 Sep 2020 17:18:31 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Jianyong Wu <jianyong.wu@....com>
Cc:     netdev@...r.kernel.org, yangbo.lu@....com, john.stultz@...aro.org,
        tglx@...utronix.de, pbonzini@...hat.com,
        sean.j.christopherson@...el.com, richardcochran@...il.com,
        Mark.Rutland@....com, will@...nel.org, suzuki.poulose@....com,
        steven.price@....com, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        kvm@...r.kernel.org, Steve.Capper@....com, justin.he@....com,
        nd@....com
Subject: Re: [PATCH v14 09/10] doc: add ptp_kvm introduction for arm64 support

On Fri, 04 Sep 2020 10:27:43 +0100,
Jianyong Wu <jianyong.wu@....com> wrote:
> 
> ptp_kvm implementation depends on hypercall using SMCCC. So we
> introduce a new SMCCC service ID. This doc explain how we define
> and use this new ID.
> 
> Signed-off-by: Jianyong Wu <jianyong.wu@....com>
> ---
>  Documentation/virt/kvm/arm/ptp_kvm.rst | 72 ++++++++++++++++++++++++++
>  1 file changed, 72 insertions(+)
>  create mode 100644 Documentation/virt/kvm/arm/ptp_kvm.rst
> 
> diff --git a/Documentation/virt/kvm/arm/ptp_kvm.rst b/Documentation/virt/kvm/arm/ptp_kvm.rst
> new file mode 100644
> index 000000000000..455591e2587a
> --- /dev/null
> +++ b/Documentation/virt/kvm/arm/ptp_kvm.rst
> @@ -0,0 +1,72 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +PTP_KVM support for arm64
> +=========================
> +
> +PTP_KVM is used for time sync between guest and host in a high precison.
> +It needs get wall time and counter value from host and transfer these data
> +to guest via hypercall service. So one more hypercall service should be
> +added.
> +
> +This new SMCCC hypercall will be defined as:
> +
> +* ARM_SMCCC_HYP_KVM_PTP_FUNC_ID: 0xC6000001
> +
> +As we only support 64-bits ptp_kvm client, so we choose SMC64/HVC64
> +calling convention.

This isn't what the code does, as it is explicitly set as an SMC32
service... Furthermore, we still run 32bit guests, and will do for the
foreseeable future. Having removed KVM support for 32bit doesn't mean
32bits are gone.

	M.

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