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

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Date: Mon, 25 Mar 2024 14:29:49 -0700
From: isaku.yamahata@...el.com
To: "Huang, Kai" <kai.huang@...el.com>
Cc: "Yamahata, Isaku" <isaku.yamahata@...el.com>,
	"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

On Mon, Mar 25, 2024 at 09:43:31PM +1300,
"Huang, Kai" <kai.huang@...el.com> wrote:

> 
> > > 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?

Sure, let me update the commit log.
-- 
Isaku Yamahata <isaku.yamahata@...el.com>