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

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Message-ID: <d4285aa9adb60b774ca1491e2a0be573e6c82c07.camel@intel.com>
Date: Tue, 10 Jun 2025 16:54:46 +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>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "Zhao, Yan Y" <yan.y.zhao@...el.com>,
	"Lindgren, Tony" <tony.lindgren@...el.com>, "Shutemov, Kirill"
	<kirill.shutemov@...el.com>, "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 Tue, 2025-06-10 at 09:50 -0700, Rick Edgecombe wrote:
> Why do we need an opt-in interface instead of a way to expose which exit's are
> supported by KVM? I would think the need for a TDVMCALL opt-in interface would
> only come up if there was a bad guest that was making TDVMCALLs that it did not
> see in GetTdVmCallInfo. So that we would actually require an opt-in is not
> guaranteed. 
> 
> Another consideration could be how to handle GetQuote for an eventual TDVMCALL
> opt-in interface, should it be needed. The problem would be GetQuote would be
> opted in by default and make the interface weird. But we may not want to have a
> TDVMCall specific opt-in interface. There could be other TDX behaviors that we
> need to opt-in around. In which case the opt-in interface could be more generic,
> and by implementing the TDVMCall opt-in interface ahead of time we would end up
> with two opt-in interfaces instead of one.
> 
> So how about just adding a field to struct kvm_tdx_capabilities to describe the
> KVM TDVMcalls? Or some other place? But don't invent an opt-in interface
> until/if we need it.

Oh, and there already is a hypercall exit opt-in interface, so
KVM_CAP_TDX_USER_EXIT_TDVMCALL would overlap with it, right?