linux-kernel - Re: [v2 2/6] KVM: arm64: Add SMCCC paravirtualised lock calls

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Message-ID: <87cz9y3avq.fsf@stealth>
Date:   Mon, 07 Nov 2022 17:58:01 +0000
From:   Punit Agrawal <punit.agrawal@...edance.com>
To:     Usama Arif <usama.arif@...edance.com>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        kvmarm@...ts.cs.columbia.edu, kvm@...r.kernel.org,
        linux-doc@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, linux@...linux.org.uk,
        yezengruan@...wei.com, catalin.marinas@....com, will@...nel.org,
        maz@...nel.org, steven.price@....com, mark.rutland@....com,
        bagasdotme@...il.com, fam.zheng@...edance.com,
        liangma@...ngbit.com, punit.agrawal@...edance.com
Subject: Re: [v2 2/6] KVM: arm64: Add SMCCC paravirtualised lock calls

Usama Arif <usama.arif@...edance.com> writes:

> Add a new SMCCC compatible hypercalls for PV lock features:
>   ARM_SMCCC_KVM_FUNC_PV_LOCK:   0xC6000002
>
> Also add the header file which defines the ABI for the paravirtualized
> lock features we're about to add.
>
> Signed-off-by: Zengruan Ye <yezengruan@...wei.com>
> Signed-off-by: Usama Arif <usama.arif@...edance.com>
> ---
>  arch/arm64/include/asm/pvlock-abi.h | 17 +++++++++++++++++
>  include/linux/arm-smccc.h           |  8 ++++++++
>  tools/include/linux/arm-smccc.h     |  8 ++++++++
>  3 files changed, 33 insertions(+)
>  create mode 100644 arch/arm64/include/asm/pvlock-abi.h
>
> diff --git a/arch/arm64/include/asm/pvlock-abi.h b/arch/arm64/include/asm/pvlock-abi.h
> new file mode 100644
> index 000000000000..3f4574071679
> --- /dev/null
> +++ b/arch/arm64/include/asm/pvlock-abi.h
> @@ -0,0 +1,17 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Copyright(c) 2019 Huawei Technologies Co., Ltd
> + * Author: Zengruan Ye <yezengruan@...wei.com>
> + *         Usama Arif <usama.arif@...edance.com>
> + */
> +
> +#ifndef __ASM_PVLOCK_ABI_H
> +#define __ASM_PVLOCK_ABI_H
> +
> +struct pvlock_vcpu_state {
> +	__le64 preempted;
> +	/* Structure must be 64 byte aligned, pad to that size */
> +	u8 padding[56];
> +} __packed;

For structure alignment, I'd have expected to see the use of "aligned"
attribute. Is there any benefit in using padding to achieve alignment?

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