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

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Message-ID: <f24b69851a0565ed6d5b284df0e7d8399e65ff69.camel@intel.com>
Date: Wed, 11 Jun 2025 14:41:41 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "Li, Xiaoyao" <xiaoyao.li@...el.com>, "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>, "Huang,
 Kai" <kai.huang@...el.com>, "Yao, Jiewen" <jiewen.yao@...el.com>, "Chatre,
 Reinette" <reinette.chatre@...el.com>, "Lindgren, Tony"
	<tony.lindgren@...el.com>, "Zhao, Yan Y" <yan.y.zhao@...el.com>, "Shutemov,
 Kirill" <kirill.shutemov@...el.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "Hunter, Adrian" <adrian.hunter@...el.com>,
	"Yamahata, Isaku" <isaku.yamahata@...el.com>
Subject: Re: [RFC PATCH 3/4] KVM: TDX: Exit to userspace for GetTdVmCallInfo

On Wed, 2025-06-11 at 22:34 +0800, Xiaoyao Li wrote:
> > What is the problem with using the existing exit opt-in interface?
> 
> It mixes up common KVM defined hypercall leafs (KVM_HC_*) with TDX 
> specific TDVMCALL leafs. Surely it can work but it just doesn't look 
> clean to me.

 - TDVMCallInfo is used to expose which TDVMCalls are expose to the guest
(clean)
 - KVM HC opt-in is used to expose which exits KVM should fwd to userspace
(seems clean to me)

There is an asymmetry in that what is returned in TDVMCallInfo can't be blindly
dumped into a KVM opt-in interface. But the logic matching TDVMCallInfo leaf <->
KVM HC needs to be somewhere. The default place should be userspace.

Did I miss anything?