linux-kernel - Re: [RFC PATCH 4/4] KVM: TDX: Check KVM exit on KVM_HC_MAP_GPA

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Message-ID: <f0d42c86e0b2fbad3fa3fdcdce214059b0581573.camel@intel.com>
Date: Wed, 11 Jun 2025 14:04:40 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "Li, Xiaoyao" <xiaoyao.li@...el.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>, "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 4/4] KVM: TDX: Check KVM exit on KVM_HC_MAP_GPA_RANGE
 when TD finalize

On Wed, 2025-06-11 at 22:01 +0800, Xiaoyao Li wrote:
> > > So, when the TDX guest calls MapGPA and KVM finds userspace doesn't opt-in
> > > KVM_HC_MAP_GPA_RANGE, just return error to userspace?
> > 
> > Why can't KVM just do what it already does, and return an error to the
> > guest?
> 
> Because GHCI requires it must be supported. No matter with the old GHCI 
> that only allows <GetTdVmCallInfo> to succeed and the success of 
> <GetTdVmCallInfo> means all the TDVMCALL leafs are support, or the 
> proposed updated GHCI that defines <MapGpa> as one of the base API/leaf, 
> and the base API must be supported by VMM.
> 
> Binbin wants to honor it.

But KVM doesn't need to support all ways that userspace could meet the GHCI
spec. If userspace opts-in to the exit, they will meet the spec. If they
configure KVM differently then they wont, but this is their decision.