linux-kernel - Re: [PATCH v19 038/130] KVM: TDX: create/destroy VM structure

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Message-ID: <ZgV6wnQcU37Jbp7W@chao-email>
Date: Thu, 28 Mar 2024 22:12:18 +0800
From: Chao Gao <chao.gao@...el.com>
To: "Huang, Kai" <kai.huang@...el.com>
CC: "Yamahata, Isaku" <isaku.yamahata@...el.com>, "Zhang, Tina"
	<tina.zhang@...el.com>, "isaku.yamahata@...ux.intel.com"
	<isaku.yamahata@...ux.intel.com>, "seanjc@...gle.com" <seanjc@...gle.com>,
	"Yuan, Hang" <hang.yuan@...el.com>, "sean.j.christopherson@...el.com"
	<sean.j.christopherson@...el.com>, "Chen, Bo2" <chen.bo@...el.com>,
	"sagis@...gle.com" <sagis@...gle.com>, "isaku.yamahata@...il.com"
	<isaku.yamahata@...il.com>, "Aktas, Erdem" <erdemaktas@...gle.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>, "pbonzini@...hat.com"
	<pbonzini@...hat.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v19 038/130] KVM: TDX: create/destroy VM structure

On Thu, Mar 28, 2024 at 11:14:42AM +0000, Huang, Kai wrote:
>> > 
>> > [...]
>> > 
>> > > > > +
>> > > > > +void tdx_mmu_release_hkid(struct kvm *kvm)
>> > > > > +{
>> > > > > +	bool packages_allocated, targets_allocated;
>> > > > > +	struct kvm_tdx *kvm_tdx = to_kvm_tdx(kvm);
>> > > > > +	cpumask_var_t packages, targets;
>> > > > > +	u64 err;
>> > > > > +	int i;
>> > > > > +
>> > > > > +	if (!is_hkid_assigned(kvm_tdx))
>> > > > > +		return;
>> > > > > +
>> > > > > +	if (!is_td_created(kvm_tdx)) {
>> > > > > +		tdx_hkid_free(kvm_tdx);
>> > > > > +		return;
>> > > > > +	}
>> > > > 
>> > > > I lost tracking what does "td_created()" mean.
>> > > > 
>> > > > I guess it means: KeyID has been allocated to the TDX guest, but not yet
>> > > > programmed/configured.
>> > > > 
>> > > > Perhaps add a comment to remind the reviewer?
>> > > 
>> > > As Chao suggested, will introduce state machine for vm and vcpu.
>> > > 
>> > > https://lore.kernel.org/kvm/ZfvI8t7SlfIsxbmT@chao-email/
>> > 
>> > Could you elaborate what will the state machine look like?
>> > 
>> > I need to understand it.
>> 
>> Not yet. Chao only propose to introduce state machine. Right now it's just an
>> idea.
>
>Then why state machine is better?  I guess we need some concrete example to tell
>which is better?

Something like the TD Life Cycle State Machine (Section 9.1 of TDX module spec[1])

[1]: https://cdrdv2.intel.com/v1/dl/getContent/733568

I don't have the code. But using a few boolean variables to track the state of
TD and VCPU looks bad and hard to maintain and extend. At least, the state machine
is well-documented.