linux-kernel - Re: [PATCH v2 0/3] TDX attestation support and GHCI fixup

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Message-ID: <CABgObfadU2_XLM8yGQrx9rDswfW3Dby10_nxzTBUdYGASQuOaw@mail.gmail.com>
Date: Fri, 20 Jun 2025 19:24:05 +0200
From: Paolo Bonzini <pbonzini@...hat.com>
To: Xiaoyao Li <xiaoyao.li@...el.com>
Cc: "Kernel Mailing List, Linux" <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>, 
	Sean Christopherson <seanjc@...gle.com>, Rick Edgecombe <rick.p.edgecombe@...el.com>, 
	"Huang, Kai" <kai.huang@...el.com>, Adrian Hunter <adrian.hunter@...el.com>, reinette.chatre@...el.com, 
	"Lindgren, Tony" <tony.lindgren@...el.com>, "Yamahata, Isaku" <isaku.yamahata@...el.com>, 
	Yan Zhao <yan.y.zhao@...el.com>, mikko.ylinen@...ux.intel.com, 
	"Shutemov, Kirill" <kirill.shutemov@...el.com>, "Yao, Jiewen" <jiewen.yao@...el.com>, 
	Binbin Wu <binbin.wu@...ux.intel.com>
Subject: Re: [PATCH v2 0/3] TDX attestation support and GHCI fixup

On Fri, Jun 20, 2025 at 2:48 PM Xiaoyao Li <xiaoyao.li@...el.com> wrote:
> > The interface I chose is that KVM always exits, but it initializes the
> > output values such that userspace can leave them untouched for unknown
> > TDVMCALLs or unknown leaves. So there is no need for this.
> >
> > Querying kernel support of other services can be added later, but
> > unless the GHCI adds more input or output fields to TdVmCallInfo there
> > is no need to limit the userspace exit to leaf 1.
>
> I meant the case where KVM is going to support another optional TDVMCALL
> leaf in the future, e.g., SetEventNotifyInterrupt. At that time,
> userspace needs to differentiate between old KVM which only supports
> <GetQuote> and new KVM which supports both <GetQuote> and
> <SetEventNotifyInterrupt>.

Yeah, I see what you mean now. Userspace cannot know which TDVMCALL
will exit, other than GET_QUOTE which we know is in the first part.

By the way I'm tempted to implement SetupEventNotifyInterrupt as well,
it's just a handful of lines of code.

Paolo