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

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Message-ID: <f633077e-a28a-4c6e-81b3-7a36044f8bae@intel.com>
Date: Fri, 20 Jun 2025 20:34:53 +0800
From: Xiaoyao Li <xiaoyao.li@...el.com>
To: Paolo Bonzini <pbonzini@...hat.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 3/3] KVM: TDX: Exit to userspace for GetTdVmCallInfo

On 6/20/2025 8:03 PM, Paolo Bonzini wrote:
> Il ven 20 giu 2025, 03:21 Xiaoyao Li <xiaoyao.li@...el.com> ha scritto:
>>
>>>                tdx->vp_enter_args.r11 = 0;
>>> +             tdx->vp_enter_args.r12 = 0;
>>>                tdx->vp_enter_args.r13 = 0;
>>>                tdx->vp_enter_args.r14 = 0;
>>> +             return 1;
>>
>> Though it looks OK to return all-0 for r12 == 0 and undefined case of
>> r12 > 1, I prefer returning TDVMCALL_STATUS_INVALID_OPERAND for
>> undefined case.
> 
> 
>  From the GHCI I wasn't sure that TDVMCALL_STATUS_INVALID_OPERAND is a
> valid result at all.

It's part of the new GHCI change, which currently is still in draft 
state. (Sorry for not informing you)

The proposed GHCI update defines VMCALL_OPERAND_INVALID for the case of 
input R12 value is not supported. So for VMM that doesn't implement the 
enumeration for the optional leafs when r12 = 1 can return this status 
code. As well, VMM can return this status code for the case of input R12 
 >= 2, to avoid the VMM introduces its own defined behavior.

> Paolo
> 
>>
>> So please make above "case 0:", and make the "default:" return
>> TDVMCALL_STATUS_INVALID_OPERAND
>>
>>>        }
>>> -     return 1;
>>>    }
>>>
>>>    static int tdx_complete_simple(struct kvm_vcpu *vcpu)
>>> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
>>> index 6708bc88ae69..fb3b4cd8d662 100644
>>> --- a/include/uapi/linux/kvm.h
>>> +++ b/include/uapi/linux/kvm.h
>>> @@ -461,6 +461,11 @@ struct kvm_run {
>>>                                        __u64 gpa;
>>>                                        __u64 size;
>>>                                } get_quote;
>>> +                             struct {
>>> +                                     __u64 ret;
>>> +                                     __u64 leaf;
>>> +                                     __u64 r11, r12, r13, r14;
>>> +                             } get_tdvmcall_info;
>>>                        };
>>>                } tdx;
>>>                /* Fix the size of the union. */
>>
> 
>