linux-kernel - Re: [PATCH 1/2] KVM: TDX: Handle TDG.VP.VMCALL<GetQuote>

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Message-ID: <ac936ff2-7a47-42b8-b144-cf54eb05274b@linux.intel.com>
Date: Tue, 8 Apr 2025 10:35:20 +0800
From: Binbin Wu <binbin.wu@...ux.intel.com>
To: "Huang, Kai" <kai.huang@...el.com>,
 "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
 "pbonzini@...hat.com" <pbonzini@...hat.com>,
 "seanjc@...gle.com" <seanjc@...gle.com>
Cc: "mikko.ylinen@...ux.intel.com" <mikko.ylinen@...ux.intel.com>,
 "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
 "Gao, Chao" <chao.gao@...el.com>, "Li, Xiaoyao" <xiaoyao.li@...el.com>,
 "Chatre, Reinette" <reinette.chatre@...el.com>,
 "Hunter, Adrian" <adrian.hunter@...el.com>,
 "Lindgren, Tony" <tony.lindgren@...el.com>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "Zhao, Yan Y" <yan.y.zhao@...el.com>,
 "Yamahata, Isaku" <isaku.yamahata@...el.com>
Subject: Re: [PATCH 1/2] KVM: TDX: Handle TDG.VP.VMCALL<GetQuote>



On 4/3/2025 6:00 AM, Huang, Kai wrote:
>>>> +via the same buffer. The 'ret' field represents the return value.
>>>>
>>> return value of the GetQuote TDVMCALL?
>> Yes, thereturn code of the GetQuote TDVMCALL.
>>>> The userspace
>>>> +should update the return value before resuming the vCPU according to TDX GHCI
>>>> +spec.
>>>>
>>> I don't quite follow.  Why userspace should "update" the return value?
>> Because only userspace knows whether the request has been queued successfully.
>>
>> According to GHCI, TDG.VP.VMCALL<GetQuote> API allows one TD to issue multiple
>> requests. This is implementation specific as to how many concurrent requests
>> are allowed.  The TD should be able to handle TDG.VP.VMCALL_RETRY if it chooses
>> to issue multiple requests simultaneously.
>> So the userspace may set the return code as TDG.VP.VMCALL_RETRY.
> OK.  How about just say:
>
> The 'ret' field represents the return value of the GetQuote request.  KVM only
> bridges the request to userspace VMM after sanity checks, and the userspace VMM
> is responsible for setting up the return value since only userspace knows
> whether the request has been queued successfully or not.
>
This looks good to me.
Regarding the sanity checks, I would appreciate inputs from others.