linux-kernel - Re: [PATCH 1/2] KVM: TDX: Handle TDG.VP.VMCALL<GetQuote>

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Message-ID: <d14777dd931996caca138c9b51c2f6c4128bdf81.camel@intel.com>
Date: Wed, 2 Apr 2025 08:58:14 +0000
From: "Huang, Kai" <kai.huang@...el.com>
To: "kvm@...r.kernel.org" <kvm@...r.kernel.org>, "pbonzini@...hat.com"
	<pbonzini@...hat.com>, "seanjc@...gle.com" <seanjc@...gle.com>,
	"binbin.wu@...ux.intel.com" <binbin.wu@...ux.intel.com>
CC: "mikko.ylinen@...ux.intel.com" <mikko.ylinen@...ux.intel.com>, "Edgecombe,
 Rick P" <rick.p.edgecombe@...el.com>, "Gao, Chao" <chao.gao@...el.com>, "Li,
 Xiaoyao" <xiaoyao.li@...el.com>, "Chatre, Reinette"
	<reinette.chatre@...el.com>, "Hunter, Adrian" <adrian.hunter@...el.com>,
	"Lindgren, Tony" <tony.lindgren@...el.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "Zhao, Yan Y" <yan.y.zhao@...el.com>,
	"Yamahata, Isaku" <isaku.yamahata@...el.com>
Subject: Re: [PATCH 1/2] KVM: TDX: Handle TDG.VP.VMCALL<GetQuote>

On Wed, 2025-04-02 at 00:53 +0000, Huang, Kai wrote:
> > 
> > KVM forwards the request to userspace VMM (e.g., QEMU) and userspace VMM
> > queues the operation asynchronously.  
> > 
> 
> I think the key is GetQuote is asynchronous therefore KVM will return to guest
> immediately after forwarding to userspace.  Whether *userspace* queues the
> operation asynchronously doesn't matter.
> 
> > After the TDVMCALL is returned and
> > back to TDX guest, TDX guest can poll the status field of the shared-memory
> > area.
> 
> How about combing the above two paragraphs into:
> 
> GetQuote is an asynchronous request.  KVM returns to userspace immediately after
> forwarding the request to userspace.  The TDX guest then needs to poll the
> status field of the shared buffer (or wait for notification if enabled) to tell
> whether the Quote is ready.

I was thinking too quickly (since needed to pickup kids) and missed that it is
*userspace* who makes the GetQuote asynchronous.  Sorry for the noise and please
ignore the above comment :-)