linux-kernel - Re: [RFC PATCH 09/21] KVM: TDX: Enable 2MB mapping size after TD is RUNNABLE

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Message-ID: <4312a9a24f187b3e2d3f2bf76b2de6c8e8d3cf91.camel@intel.com>
Date: Fri, 13 Jun 2025 23:33:48 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
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Subject: Re: [RFC PATCH 09/21] KVM: TDX: Enable 2MB mapping size after TD is
 RUNNABLE

On Fri, 2025-06-13 at 15:19 -0700, Sean Christopherson wrote:
> > Arg, I just realized a one-way opt-in will have a theoretical gap. If the
> > guest
> > kexec's, the new kernel will need to match the opt-in.
> 
> All the more reason to make this a property of the VM that is passed via
> "struct td_params".  I.e. put the onus on the owner of the VM to ensure their
> kernel(s) have been updated accordingly.

Hmm, it gives me pause. At minimum it should have an enumeration to the guest.

> 
> I understand that this could be painful, but honestly _all_ of TDX and SNP is
> painful for the guest.  E.g. I don't think it's any worse than the security
> issues with TDX (and SNP) guests using kvmclock (which I'd love some reviews
> on,
> btw).
> 
> https://lore.kernel.org/all/20250227021855.3257188-35-seanjc@google.com

Oh, nice. I hadn't seen this. Agree that a comprehensive guest setup is quite
manual. But here we are playing with guest ABI. In practice, yes it's similar to
passing yet another arg to get a good TD.

We can start with a prototype the host side arg and see how it turns out. I
realized we need to verify edk2 as well.

Thanks Sean.