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SubjectRe: [v2 2/6] KVM: arm64: Add SMCCC paravirtualised lock calls
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On 07/11/2022 17:58, Punit Agrawal wrote:
> Usama Arif <usama.arif@bytedance.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@huawei.com>
>> Signed-off-by: Usama Arif <usama.arif@bytedance.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@huawei.com>
>> + * Usama Arif <usama.arif@bytedance.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)));


> [...]
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