linux-kernel - Re: [PATCH v19 130/130] RFC: KVM: x86, TDX: Add check for KVM_SET

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Date: Mon, 25 Mar 2024 15:32:59 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "Huang, Kai"
	<kai.huang@...el.com>, "Yamahata, Isaku" <isaku.yamahata@...el.com>
CC: "Zhang, Tina" <tina.zhang@...el.com>, "seanjc@...gle.com"
	<seanjc@...gle.com>, "Yuan, Hang" <hang.yuan@...el.com>, "Chen, Bo2"
	<chen.bo@...el.com>, "sagis@...gle.com" <sagis@...gle.com>,
	"isaku.yamahata@...il.com" <isaku.yamahata@...il.com>, "Aktas, Erdem"
	<erdemaktas@...gle.com>, "pbonzini@...hat.com" <pbonzini@...hat.com>
Subject: Re: [PATCH v19 130/130] RFC: KVM: x86, TDX: Add check for
 KVM_SET_CPUID2

On Mon, 2024-03-25 at 11:14 +0000, Huang, Kai wrote:
> To confirm, I mean you want to simply make KVM_SET_CPUID2 return error for TDX
> guest?
> 
> It is acceptable to me, and I don't see any conflict with Sean's comments.
> 
> But I don't know Sean's perference.  As he said, I think  the consistency
> checking is quite straight-forward:
> 
> "
> It's not complicated at all.  Walk through the leafs defined during
> TDH.MNG.INIT, reject KVM_SET_CPUID if a leaf isn't present or doesn't match
> exactly.
> "
> 
Yea, I'm just thinking if we could take two patches down to one small one it might be a way to
essentially break off this work to another series without affecting the ability to boot a TD. It
*seems* to be the way things are going.

> So to me it's not a big deal. 
> 
> Either way, we need a patch to handle SET_CPUID2:
> 
> 1) if we go option 1) -- that is reject SET_CPUID2 completely -- we need to make
> vcpu's CPUID point to KVM's saved CPUID during TDH.MNG.INIT.

Ah, I missed this part. Can you elaborate? By dropping these two patches it doesn't prevent a TD
boot. If we then reject SET_CPUID, this will break things unless we make other changes? And they are
not small?