linux-kernel - Re: [RFC PATCH 3/4] KVM: TDX: Exit to userspace for GetTdVmCallInfo

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Message-ID: <089eeacb231f3afa04f81b9d5ddbb98b6d901565.camel@intel.com>
Date: Wed, 11 Jun 2025 16:53:19 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "seanjc@...gle.com" <seanjc@...gle.com>
CC: "mikko.ylinen@...ux.intel.com" <mikko.ylinen@...ux.intel.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "Huang, Kai"
	<kai.huang@...el.com>, "binbin.wu@...ux.intel.com"
	<binbin.wu@...ux.intel.com>, "Yao, Jiewen" <jiewen.yao@...el.com>, "Li,
 Xiaoyao" <xiaoyao.li@...el.com>, "Lindgren, Tony" <tony.lindgren@...el.com>,
	"Hunter, Adrian" <adrian.hunter@...el.com>, "Chatre, Reinette"
	<reinette.chatre@...el.com>, "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"Zhao, Yan Y" <yan.y.zhao@...el.com>, "Yamahata, Isaku"
	<isaku.yamahata@...el.com>, "pbonzini@...hat.com" <pbonzini@...hat.com>,
	"Shutemov, Kirill" <kirill.shutemov@...el.com>
Subject: Re: [RFC PATCH 3/4] KVM: TDX: Exit to userspace for GetTdVmCallInfo

On Wed, 2025-06-11 at 09:26 -0700, Sean Christopherson wrote:
> > GetQuote is not part of the "Base" TDVMCALLs and so has a bit in
> > GetTdVmCallInfo. We could move it to base?
> 
> Is GetQuote actually optional?  TDX without attestation seems rather
> pointless.

I don't know if that was a consideration for why it got added to the optional
category. The inputs were gathered from more than just Linux.

> 
> > Paolo seemed keen on GetTdVmCallInfo exiting to userspace, but this was
> > before
> > the spec overhaul.
> 
> If GetQuote is truly optional, then exiting to userspace makes sense.  But as
> above, that seems odd to me.

Let us check on adding it to the "base" TDVMCALLs. If there is some good reason,
we can post v2 with GetTdVmCallInfo exiting. This will probably be Friday due to
the required people being out. Does it work for the timelines?

Under the change to add GetQuote to the base TDVMCALLs, patch 1 and 2 would be
the only changes anyway. It starts to feel a little fast and loose, but another
option is just to take patches 1 and 2, and we can finalize GetTdVmCallInfo at
whatever pace is best. 

Xiaoyao, Binbin do you see any pitfalls to that? If we add GetTdVmCallInfo as a
new exit, and we could add the supported TDVMCALLs to struct
kvm_tdx_capabilities at that point. If it doesn't make it for 6.16, it gets an
opt-in.