linux-kernel - Re: [PATCH v19 037/130] KVM: TDX: Make KVM_CAP_MAX

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Message-ID: <d4014bb8-168e-4147-9554-bab22b0f4afe@intel.com>
Date: Mon, 25 Mar 2024 21:43:31 +1300
From: "Huang, Kai" <kai.huang@...el.com>
To: "Yamahata, Isaku" <isaku.yamahata@...el.com>
CC: "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"isaku.yamahata@...il.com" <isaku.yamahata@...il.com>, Paolo Bonzini
	<pbonzini@...hat.com>, "Aktas, Erdem" <erdemaktas@...gle.com>, "Sean
 Christopherson" <seanjc@...gle.com>, Sagi Shahar <sagis@...gle.com>, "Chen,
 Bo2" <chen.bo@...el.com>, "Yuan, Hang" <hang.yuan@...el.com>, "Zhang, Tina"
	<tina.zhang@...el.com>, "isaku.yamahata@...ux.intel.com"
	<isaku.yamahata@...ux.intel.com>
Subject: Re: [PATCH v19 037/130] KVM: TDX: Make KVM_CAP_MAX_VCPUS backend
 specific


>> Currently, the KVM x86 always reports KVM_MAX_VCPUS for all VMs but doesn't
>> allow to enable KVM_CAP_MAX_VCPUS to configure the number of maximum vcpus
>                                                       maximum number of vcpus
>> on VM-basis.
>>
>> Add "per-VM maximum vcpus" to KVM x86/TDX to accommodate TDX's needs.
>>
>> The userspace-configured value then can be verified when KVM is actually
>                                               used
>> creating the TDX guest.
>> "

I think we still have two options regarding to how 'max_vcpus' is 
handled in ioctl() to do TDH.MNG.INIT:

1) Just use the 'max_vcpus' done in KVM_ENABLE_CAP(KVM_CAP_MAX_VCPUS),
2) Still pass the 'max_vcpus' as input, but KVM verifies it against the 
value that is saved in KVM_ENABLE_CAP(KVM_CAP_MAX_VCPUS).

2) seems unnecessary, so I don't have objection to use 1).  But it seems 
we could still mention it in the changelog in that patch?