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

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Message-ID: <0bd315344080e71ace8f517f8f45e41c1a7badf0.camel@intel.com>
Date: Fri, 11 Jul 2025 23:04:23 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "seanjc@...gle.com" <seanjc@...gle.com>
CC: "Gao, Chao" <chao.gao@...el.com>, "Huang, Kai" <kai.huang@...el.com>,
	"binbin.wu@...ux.intel.com" <binbin.wu@...ux.intel.com>, "Li, Xiaoyao"
	<xiaoyao.li@...el.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "Hunter, Adrian" <adrian.hunter@...el.com>,
	"kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>, "pbonzini@...hat.com"
	<pbonzini@...hat.com>, "Chatre, Reinette" <reinette.chatre@...el.com>,
	"Yamahata, Isaku" <isaku.yamahata@...el.com>, "Zhao, Yan Y"
	<yan.y.zhao@...el.com>, "tony.lindgren@...ux.intel.com"
	<tony.lindgren@...ux.intel.com>
Subject: Re: [PATCH V4 0/1] KVM: TDX: Decrease TDX VM shutdown time

On Fri, 2025-07-11 at 15:54 -0700, Sean Christopherson wrote:
> > 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.

There are tons of arch specific caps. Can you help me understand this point a
little more? Is TDX special compared to the other arch specific ones?

> 
> > 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.

I guess. It's new place to check for the same type of information that caps
currently provides. Not a big deal either way to me though.

> 
> > 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.

Ok.