linux-kernel - Re: [RFC PATCH v5 026/104] KVM: TDX: x86: Add vm ioctl to get TDX systemwide parameters

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Message-ID: <8aa0cf5b-bfda-bcf8-45f9-dc5113532caa@intel.com>
Date:   Thu, 7 Apr 2022 09:17:51 +0800
From:   Xiaoyao Li <xiaoyao.li@...el.com>
To:     Kai Huang <kai.huang@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>, isaku.yamahata@...el.com,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     isaku.yamahata@...il.com, Jim Mattson <jmattson@...gle.com>,
        erdemaktas@...gle.com, Connor Kuehl <ckuehl@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>
Subject: Re: [RFC PATCH v5 026/104] KVM: TDX: x86: Add vm ioctl to get TDX
 systemwide parameters

On 4/7/2022 9:07 AM, Kai Huang wrote:
> On Wed, 2022-04-06 at 09:54 +0800, Xiaoyao Li wrote:
>> On 4/5/2022 8:52 PM, Paolo Bonzini wrote:
>>> On 3/4/22 20:48, isaku.yamahata@...el.com wrote:
>>>> Implement a VM-scoped subcomment to get system-wide parameters.  Although
>>>> this is system-wide parameters not per-VM, this subcomand is VM-scoped
>>>> because
>>>> - Device model needs TDX system-wide parameters after creating KVM VM.
>>>> - This subcommands requires to initialize TDX module.  For lazy
>>>>     initialization of the TDX module, vm-scope ioctl is better.
>>>
>>> Since there was agreement to install the TDX module on load, please
>>> place this ioctl on the /dev/kvm file descriptor.
>>>
>>> At least for SEV, there were cases where the system-wide parameters are
>>> needed outside KVM, so it's better to avoid requiring a VM file descriptor.
>>
>> I don't have strong preference on KVM-scope ioctl or VM-scope.
>>
>> Initially, we made it KVM-scope and change it to VM-scope in this
>> version. Yes, it returns the info from TDX module, which doesn't vary
>> per VM. However, what if we want to return different capabilities
>> (software controlled capabilities) per VM?
>>
> 
> In this case, you don't return different capabilities, instead, you return the
> same capabilities but control the capabilities on per-VM basis.

yes, so I'm not arguing it or insisting on per-VM.

I just speak out my concern since it's user ABI.

>> Part of the TDX capabilities
>> serves like get_supported_cpuid, making it KVM wide lacks the
>> flexibility to return differentiated capabilities for different TDs.
>>
>>
>>> Thanks,
>>>
>>> Paolo
>>>
>>
>