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Message-ID: <72e34f84-5bea-8f69-6699-29e2970c80b4@arm.com>
Date: Mon, 17 Aug 2020 10:49:12 +0100
From: Steven Price <steven.price@....com>
To: zhukeqian <zhukeqian1@...wei.com>, Marc Zyngier <maz@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
kvmarm@...ts.cs.columbia.edu, kvm@...r.kernel.org,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>,
James Morse <james.morse@....com>,
Suzuki K Poulose <suzuki.poulose@....com>,
wanghaibin.wang@...wei.com
Subject: Re: [PATCH 2/3] KVM: uapi: Remove KVM_DEV_TYPE_ARM_PV_TIME in
kvm_device_type
On 17/08/2020 09:43, zhukeqian wrote:
> Hi Marc,
>
> On 2020/8/17 15:39, Marc Zyngier wrote:
>> On 2020-08-17 04:37, Keqian Zhu wrote:
>>> ARM64 PV-time ST is configured by userspace through vCPU attribute,
>>> and KVM_DEV_TYPE_ARM_PV_TIME is unused.
>>>
>>> Signed-off-by: Keqian Zhu <zhukeqian1@...wei.com>
>>> ---
>>> include/uapi/linux/kvm.h | 2 --
>>> tools/include/uapi/linux/kvm.h | 2 --
>>> 2 files changed, 4 deletions(-)
>>>
>>> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
>>> index 4fdf303..9a6b97e 100644
>>> --- a/include/uapi/linux/kvm.h
>>> +++ b/include/uapi/linux/kvm.h
>>> @@ -1258,8 +1258,6 @@ enum kvm_device_type {
>>> #define KVM_DEV_TYPE_ARM_VGIC_ITS KVM_DEV_TYPE_ARM_VGIC_ITS
>>> KVM_DEV_TYPE_XIVE,
>>> #define KVM_DEV_TYPE_XIVE KVM_DEV_TYPE_XIVE
>>> - KVM_DEV_TYPE_ARM_PV_TIME,
>>> -#define KVM_DEV_TYPE_ARM_PV_TIME KVM_DEV_TYPE_ARM_PV_TIME
>>> KVM_DEV_TYPE_MAX,
>>> };
>>>
>>> diff --git a/tools/include/uapi/linux/kvm.h b/tools/include/uapi/linux/kvm.h
>>> index 4fdf303..9a6b97e 100644
>>> --- a/tools/include/uapi/linux/kvm.h
>>> +++ b/tools/include/uapi/linux/kvm.h
>>> @@ -1258,8 +1258,6 @@ enum kvm_device_type {
>>> #define KVM_DEV_TYPE_ARM_VGIC_ITS KVM_DEV_TYPE_ARM_VGIC_ITS
>>> KVM_DEV_TYPE_XIVE,
>>> #define KVM_DEV_TYPE_XIVE KVM_DEV_TYPE_XIVE
>>> - KVM_DEV_TYPE_ARM_PV_TIME,
>>> -#define KVM_DEV_TYPE_ARM_PV_TIME KVM_DEV_TYPE_ARM_PV_TIME
>>> KVM_DEV_TYPE_MAX,
>>> };
>>
>> No. You can't drop anything from UAPI, used or not. Doing so will
>> break the compilation of any userspace that, for any reason, references
>> this value. We cannot reuse this value in the future either, as it would
>> create a we wouldn't know which device to create.
>>
>> It is pretty unfortunate that PV time has turned into such a train wreck,
>> but that's what we have now, and it has to stay.
> Well, I see. It is a sad thing indeed.
Sorry about that, this got refactored so many times I guess I lost track
of what was actually needed and this hunk remained when it should have
been removed.
I would hope that I'm the only one who has any userspace code which uses
this, but I guess we should still be cautious since this has been in
several releases now.
Steve
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