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

[Usama Arif]

On 07/11/2022 17:58, Punit Agrawal wrote:
> Usama Arif <usama.arif@xxxxxxxxxxxxx> 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@xxxxxxxxxx>
> > Signed-off-by: Usama Arif <usama.arif@xxxxxxxxxxxxx>
> > ---
> >   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@xxxxxxxxxx>
> > + *         Usama Arif <usama.arif@xxxxxxxxxxxxx>
> > + */
> > +
> > +#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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