linux-kernel - Re: [PATCH v19 105/130] KVM: TDX: handle KVM hypercall with TDG.VP.VMCALL

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Date: Mon, 27 May 2024 08:57:28 +0800
From: Binbin Wu <binbin.wu@...ux.intel.com>
To: Isaku Yamahata <isaku.yamahata@...el.com>,
 Paolo Bonzini <pbonzini@...hat.com>, Sean Christopherson <seanjc@...gle.com>
Cc: Chao Gao <chao.gao@...el.com>, kvm@...r.kernel.org,
 linux-kernel@...r.kernel.org, isaku.yamahata@...il.com,
 erdemaktas@...gle.com, Sagi Shahar <sagis@...gle.com>,
 Kai Huang <kai.huang@...el.com>, chen.bo@...el.com, hang.yuan@...el.com,
 tina.zhang@...el.com, isaku.yamahata@...ux.intel.com
Subject: Re: [PATCH v19 105/130] KVM: TDX: handle KVM hypercall with
 TDG.VP.VMCALL



On 4/17/2024 3:02 PM, Isaku Yamahata wrote:
> On Wed, Apr 17, 2024 at 02:16:57PM +0800,
> Binbin Wu <binbin.wu@...ux.intel.com> wrote:
>
>>
>> On 4/4/2024 9:27 AM, Isaku Yamahata wrote:
>>> On Tue, Apr 02, 2024 at 04:52:46PM +0800,
>>> Chao Gao <chao.gao@...el.com> wrote:
>>>
>>>>> +static int tdx_emulate_vmcall(struct kvm_vcpu *vcpu)
>>>>> +{
>>>>> +	unsigned long nr, a0, a1, a2, a3, ret;
>>>>> +
>>>> do you need to emulate xen/hyper-v hypercalls here?
>>> No. kvm_emulate_hypercall() handles xen/hyper-v hypercalls,
>>> __kvm_emulate_hypercall() doesn't.
>> So for TDX, kvm doesn't support xen/hyper-v, right?
>>
>> Then, should KVM_CAP_XEN_HVM and KVM_CAP_HYPERV be filtered out for TDX?
> That's right. We should update kvm_vm_ioctl_check_extension() and
> kvm_vcpu_ioctl_enable_cap().  I didn't pay attention to them.
Currently, QEMU checks the capabilities for Hyper-v/Xen via 
kvm_check_extension(), which is the global version.
Only modifications in KVM can't hide these capabilities. It needs 
userspace to use VM or vCPU version to check the capabilities for 
Hyper-v and Xen.
Is it a change of ABI when the old global version is still workable, but 
userspace switches to use VM/vCPU version to check capabilities for 
Hyper-v and Xen?
Are there objections if both QEMU and KVM are modified in order to 
hide Hyper-v/Xen capabilities for TDX?