Re: [PATCH V4 0/1] KVM: TDX: Decrease TDX VM shutdown time

[Sean Christopherson <seanjc@google.com>]

On Fri, Jul 11, 2025, Rick P Edgecombe wrote:
> On Fri, 2025-07-11 at 07:19 -0700, Sean Christopherson wrote:
> > > > Bugger, you're right.  It's sitting at the top of 'kvm-x86 vmx', so it
> > > > should be
> > > > easy enough to tack on a capability.
> > > > 
> > > > This?
> > > 
> > > I'm wondering if we need a TDX centralized enumeration interface, e.g., new
> > > field in struct kvm_tdx_capabilities. I believe there will be more and more
> > > TDX new features, and assigning each a KVM_CAP seems wasteful.
> > 
> > Oh, yeah, that's a much better idea.  In addition to not polluting KVM_CAP,
> 
> How do you guys see it as wasteful? The highest cap is currently 242. For 32 bit
> KVM that leaves 2147483405 caps. If we create an interface we grow some code and
> docs, and get 64 additional ones for TDX only.

It bleeds TDX details into arch neutral code.

> The less interfaces the better I say, so KVM_CAP_TDX_TERMINATE_VM seems better.

But we already have KVM_TDX_CAPABILITIES.  This isn't really a new interface, it's
a new field in a pre-existing interface.

> Xiaoyao, is this something QEMU needs? Or more of a completeness kind of thing?

Required by VMMs.  KVM always needs to be able enumerate its new features.  We
absolutely do not want userspace making guesses based on e.g. kernel version.