Re: [PATCH v5 07/17] KVM: x86: add fields to struct kvm_arch for CoCo features

[Sean Christopherson <seanjc@google.com>]

On Tue, Apr 09, 2024, Paolo Bonzini wrote:
> On Tue, Apr 9, 2024 at 3:21 AM Sean Christopherson <seanjc@google.com> wrote:
> > > I'm a little late to this conversation, so hopefully not just complicating
> > > things. But why not deduce has_private_mem and has_protected_state from the
> > > vm_type during runtime? Like if kvm.arch.vm_type was instead a bit mask with
> > > the bit position of the KVM_X86_*_VM set, kvm_arch_has_private_mem() could
> > > bitwise-and with a compile time mask of vm_types that have primate memory.
> > > This also prevents it from ever transitioning through non-nonsensical states
> > > like vm_type == KVM_X86_TDX_VM, but !has_private_memory, so would be a little
> > > more robust.
> >
> > LOL, time is a circle, or something like that.  Paolo actually did this in v2[*],
> > and I objected, vociferously.
> 
> To be fair, Rick is asking for something much less hideous - just set
> 
>  kvm->arch.vm_type = (1 << vm_type);
> 
> and then define kvm_has_*(kvm) as !!(kvm->arch.vm_type & SOME_BIT_MASK).
> 
> And indeed it makes sense as an alternative.

Ah, yeah, I'd be fine with that. 

> It also feels a little bit more restrictive and the benefit is small, so I
> think I'm going to go with this version.

+1