linux-kernel - Re: [PATCH v2 24/25] KVM: x86: Introduce KVM_TDX_GET

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Message-ID: <71bf1ef3-ade3-4a0c-9ec3-d095e652731a@intel.com>
Date: Wed, 22 Jan 2025 15:43:54 +0800
From: Xiaoyao Li <xiaoyao.li@...el.com>
To: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
 "pbonzini@...hat.com" <pbonzini@...hat.com>,
 "seanjc@...gle.com" <seanjc@...gle.com>
Cc: "Huang, Kai" <kai.huang@...el.com>,
 "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
 "Chatre, Reinette" <reinette.chatre@...el.com>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "Zhao, Yan Y" <yan.y.zhao@...el.com>,
 "isaku.yamahata@...il.com" <isaku.yamahata@...il.com>,
 "tony.lindgren@...ux.intel.com" <tony.lindgren@...ux.intel.com>
Subject: Re: [PATCH v2 24/25] KVM: x86: Introduce KVM_TDX_GET_CPUID

On 1/22/2025 4:24 AM, Edgecombe, Rick P wrote:
> On Fri, 2025-01-10 at 12:47 +0800, Xiaoyao Li wrote:
>> 0x1f needs clarification here.
>>
>> If it's going to use the maximum leaf KVM can support, it should be 0x24
>> to align with __do_cpuid_func().
>>
>> alternatively, it can use the EAX value of leaf 0 returned by TDX
>> module. That is the value TDX module presents to the TD guest.
>>
>>> +		output_e = &td_cpuid->entries[i];
>>> +		i += tdx_vcpu_get_cpuid_leaf(vcpu, leaf,
>>> +					     KVM_MAX_CPUID_ENTRIES - i - 1,
>>> +					     output_e);
>>> +	}
>>> +
>>> +	for (leaf = 0x80000000; leaf <= 0x80000008; leaf++) {
>>> +		output_e = &td_cpuid->entries[i];
>>> +		i += tdx_vcpu_get_cpuid_leaf(vcpu, leaf,
>>> +					     KVM_MAX_CPUID_ENTRIES - i - 1,
>>> +					     output_e);
> 
> Since we are not filtering by KVM supported features anymore, maybe just use the
> max leaf for the host CPU, like:

host value is not matched with the value returned by TDX module.
I.e., On my SPR machine, the boot_cpu_data.cpuid_level is 0x20, while 
TDX module returns 0x23. It at least fails to report the leaf 0x21 to 
userspace, which is a always valid leaf for TD guest.

> @@ -2790,14 +2791,14 @@ static int tdx_vcpu_get_cpuid(struct kvm_vcpu *vcpu,
> struct kvm_tdx_cmd *cmd)
>          if (!td_cpuid)
>                  return -ENOMEM;
>   
> -       for (leaf = 0; leaf <= 0x1f; leaf++) {
> +       for (leaf = 0; leaf <= boot_cpu_data.cpuid_level; leaf++) {
>                  output_e = &td_cpuid->entries[i];
>                  i += tdx_vcpu_get_cpuid_leaf(vcpu, leaf,
>                                               KVM_MAX_CPUID_ENTRIES - i - 1,
>                                               output_e);
>          }
>   
> -       for (leaf = 0x80000000; leaf <= 0x80000008; leaf++) {
> +       for (leaf = 0x80000000; leaf <= boot_cpu_data.extended_cpuid_level;
> leaf++) {
>                  output_e = &td_cpuid->entries[i];
>                  i += tdx_vcpu_get_cpuid_leaf(vcpu, leaf,
>                                               KVM_MAX_CPUID_ENTRIES - i - 1,
>