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

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Date:   Mon, 7 Nov 2022 18:08:45 +0000
From:   Usama Arif <usama.arif@...edance.com>
To:     Punit Agrawal <punit.agrawal@...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
Subject: Re: [v2 2/6] KVM: arm64: Add SMCCC paravirtualised lock calls



On 07/11/2022 17:58, Punit Agrawal wrote:
> 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?
> 
Just made it consistent with pvclock-abi.h. If its more appropriate, can 
change to aligned in next patchset:

diff --git a/arch/arm64/include/asm/pvlock-abi.h 
b/arch/arm64/include/asm/pvlock-abi.h
index 3f4574071679..bacec4cb927a 100644
--- a/arch/arm64/include/asm/pvlock-abi.h
+++ b/arch/arm64/include/asm/pvlock-abi.h
@@ -11,7 +11,6 @@
  struct pvlock_vcpu_state {
         __le64 preempted;
         /* Structure must be 64 byte aligned, pad to that size */
-       u8 padding[56];
-} __packed;
+} __attribute__((aligned(64)));


> [...]