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

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Message-ID: <effb33d4277c47ffcc6d69b71348e3b7ea8a2740.camel@intel.com>
Date: Wed, 11 Jun 2025 14:58:33 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "Li, Xiaoyao" <xiaoyao.li@...el.com>, "seanjc@...gle.com"
	<seanjc@...gle.com>
CC: "mikko.ylinen@...ux.intel.com" <mikko.ylinen@...ux.intel.com>, "Huang,
 Kai" <kai.huang@...el.com>, "binbin.wu@...ux.intel.com"
	<binbin.wu@...ux.intel.com>, "Yao, Jiewen" <jiewen.yao@...el.com>, "Chatre,
 Reinette" <reinette.chatre@...el.com>, "Lindgren, Tony"
	<tony.lindgren@...el.com>, "Hunter, Adrian" <adrian.hunter@...el.com>, "Zhao,
 Yan Y" <yan.y.zhao@...el.com>, "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"pbonzini@...hat.com" <pbonzini@...hat.com>, "Yamahata, Isaku"
	<isaku.yamahata@...el.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "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 07:54 -0700, Sean Christopherson wrote:
> > Let's see what Paolo and Sean will say.
> 
> Kicking this to userspace seems premature.  AIUI, no "optional" VMCALL
> features
> are defined at this time, i.e. there's nothing to enumerate.  And there's no
> guarantee that there will ever be capabilties that require enumeration from 
> *userspace*.  E.g. if fancy feature XYZ requires enumeration, but that feature
> requires explicit KVM support, then forcing userspace will be messy.
> 
> So I don't see why KVM should anything other than return '0' to the guest (or
> whatever value says "there's nothing here").

GetQuote is not part of the "Base" TDVMCALLs and so has a bit in
GetTdVmCallInfo. We could move it to base?

Paolo seemed keen on GetTdVmCallInfo exiting to userspace, but this was before
the spec overhaul.