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

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Date:   Thu, 07 Apr 2022 13:07:38 +1200
From:   Kai Huang <kai.huang@...el.com>
To:     Xiaoyao Li <xiaoyao.li@...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 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.

> 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
> > 
>