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: <20220408005849.GD2864606@ls.amr.corp.intel.com>
Date:   Thu, 7 Apr 2022 17:58:49 -0700
From:   Isaku Yamahata <isaku.yamahata@...il.com>
To:     Xiaoyao Li <xiaoyao.li@...el.com>
Cc:     Kai Huang <kai.huang@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>, isaku.yamahata@...el.com,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        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 Thu, Apr 07, 2022 at 09:17:51AM +0800,
Xiaoyao Li <xiaoyao.li@...el.com> wrote:

> 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.

The reason why I made this API to VM-scope API is to reduce the number of patch
given qemu usage.  Now Paolo requested it, I'll change it KVM-scope API.
-- 
Isaku Yamahata <isaku.yamahata@...il.com>