Re: [PATCH v19 130/130] RFC: KVM: x86, TDX: Add check for KVM_SET_CPUID2

[Isaku Yamahata]

On Mon, Mar 25, 2024 at 03:32:59PM +0000,
"Edgecombe, Rick P" <rick.p.edgecombe@xxxxxxxxx> wrote:

> 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?

If we go forthis, the extended topology enumeration (cpuid[0xb or 0x1f]) would
need special handling because it's per-vcpu. not TD wide.
-- 
Isaku Yamahata <isaku.yamahata@xxxxxxxxx>