linux-kernel - Re: [PATCH 10/25] KVM: TDX: Initialize KVM supported capabilities when module setup

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Message-ID: <7ddf7841-7872-4e7b-9194-25c529bd0ae1@linux.intel.com>
Date: Tue, 13 Aug 2024 15:24:32 +0800
From: Binbin Wu <binbin.wu@...ux.intel.com>
To: Chao Gao <chao.gao@...el.com>, Rick Edgecombe <rick.p.edgecombe@...el.com>
Cc: seanjc@...gle.com, pbonzini@...hat.com, kvm@...r.kernel.org,
 kai.huang@...el.com, isaku.yamahata@...il.com,
 tony.lindgren@...ux.intel.com, xiaoyao.li@...el.com,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 10/25] KVM: TDX: Initialize KVM supported capabilities
 when module setup




On 8/13/2024 11:25 AM, Chao Gao wrote:
> On Mon, Aug 12, 2024 at 03:48:05PM -0700, Rick Edgecombe wrote:
>> From: Xiaoyao Li <xiaoyao.li@...el.com>
>>
>> While TDX module reports a set of capabilities/features that it
>> supports, what KVM currently supports might be a subset of them.
>> E.g., DEBUG and PERFMON are supported by TDX module but currently not
>> supported by KVM.
>>
>> Introduce a new struct kvm_tdx_caps to store KVM's capabilities of TDX.
>> supported_attrs and suppported_xfam are validated against fixed0/1
>> values enumerated by TDX module. Configurable CPUID bits derive from TDX
>> module plus applying KVM's capabilities (KVM_GET_SUPPORTED_CPUID),
>> i.e., mask off the bits that are configurable in the view of TDX module
>> but not supported by KVM yet.
>>
>> KVM_TDX_CPUID_NO_SUBLEAF is the concept from TDX module, switch it to 0
>> and use KVM_CPUID_FLAG_SIGNIFCANT_INDEX, which are the concept of KVM.
> If we convert KVM_TDX_CPUID_NO_SUBLEAF to 0 when reporting capabilities to
> QEMU, QEMU cannot distinguish a CPUID subleaf 0 from a CPUID w/o subleaf.
> Does it matter to QEMU?

According to "and use KVM_CPUID_FLAG_SIGNIFCANT_INDEX, which are the
concept of KVM". IIUC, KVM's ABI uses KVM_CPUID_FLAG_SIGNIFCANT_INDEX
in flags of struct kvm_cpuid_entry2 to distinguish whether the index
is significant.