linux-kernel - Re: [PATCH v5 18/22] KVM: arm64: Support SDEI ioctl commands on VM

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Message-ID: <17119a1b-9fb1-2a15-ac19-8f4e128288f5@redhat.com>
Date:   Fri, 25 Mar 2022 18:14:23 +0800
From:   Gavin Shan <gshan@...hat.com>
To:     Oliver Upton <oupton@...gle.com>
Cc:     kvmarm@...ts.cs.columbia.edu, maz@...nel.org,
        linux-kernel@...r.kernel.org, eauger@...hat.com,
        shan.gavin@...il.com, Jonathan.Cameron@...wei.com,
        pbonzini@...hat.com, vkuznets@...hat.com, will@...nel.org
Subject: Re: [PATCH v5 18/22] KVM: arm64: Support SDEI ioctl commands on VM

Hi Oliver,

On 3/25/22 3:35 PM, Oliver Upton wrote:
> On Fri, Mar 25, 2022 at 02:59:52PM +0800, Gavin Shan wrote:
>>> The PSCI implementation is a great example of how KVM has grown its
>>> implementation in line with a specification, all the while preserving
>>> backwards compatibility.
>>>
>>
>> The only information feed by VMM is the exposed events. The events
>> can't be registered from guest kernel, and raised from host to guest
>> kernel until it's exposed by VMM.
> 
> I would suggest assuming that all SDEI events are exposed by default in
> KVM. We will not require a VMM change to enable events individually.
> 

Ok, it was exactly what I did in v4, but the event is exposed
by VMM in v5. In v6, it will be staticly defined again :)

>> Besides, the exposed events will
>> be defined staticly in host/KVM as we discussed on PATCH[02/22]. We
>> also discussed to eliminate those ioctl commands. So I think we needn't
>> to add KVM_SDEI_CMD_SET_VERSION. Further more, the version is only a
>> concern to host itself if the migration can be done through the
>> firmware pseudo system registers since the migration compatibility
>> is the only concern to VMM (QEMU).
> 
> This all needs to work just like the KVM_REG_ARM_PSCI_VERSION version,
> I'd recommend taking a look at how we handle that register in KVM.
> 

Ok. I will do necessary investigation :)

>> Yes, Currently, 0.1/0.2/1.0 versions are supported by PSCI. 0.1 is
>> picked until VMM asks for 0.2 and 1.0 explicitly. However, it seems
>> QEMU isn't using 1.0 PSCI yet and maybe more patch is needed to enable
>> it.
> 
> As far as how it interacts with KVM, QEMU looks fine. The name of the
> KVM_ARM_VCPU_PSCI_0_2 bit is quite frustrating. It actually implies that
> KVM will enable it highest supported PSCI version. If the feature bit is
> cleared then you only get PSCIv0.1
> 
> However, the DT node that QEMU sets up looks a bit crusty. The
> properties for conveying PSCI function IDs were only ever necessary for
> PSCIv0.1. The only property of interest any more is 'method', to convey
> the SMCCC conduit instruction.
> 

Ok, Thanks again for the further information about PSCI implementation.
I will go through the code when I have free cycyles :)

Thanks,
Gavin