linux-kernel - Re: [PATCH 4/4] x86/tdx: Enable ENUM

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Date: Mon, 11 Mar 2024 14:05:39 +0200
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To: 
	Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
Cc: tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, 
	dave.hansen@...el.com, hpa@...or.com, seanjc@...gle.com, ele.reshetova@...el.com, 
	rick.p.edgecombe@...el.com, x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] x86/tdx: Enable ENUM_TOPOLOGY

On Sat, Mar 09, 2024 at 07:56:11PM -0800, Kuppuswamy Sathyanarayanan wrote:
> 
> On 3/9/24 1:02 PM, Kirill A. Shutemov wrote:
> > TDX 1.0 generates a #VE when accessing topology-related CPUID leafs
> > (0xB and 0x1F) and the X2APIC_APICID MSR. The kernel returns all
> > zeros on CPUID #VEs. In practice, this means that the kernel can only
> > boot with a plain topology. Any complications will cause problems.
> 
> Is this issue only for TDX 1.0? What about TDX > 1.0?

TDX 1.0 defines the baseline for TDX. Any change in behaviour will be
gated by explicit opt-in. In this case, it is ENUM_TOPOLOGY.

> > The ENUM_TOPOLOGY feature allows the VMM to provide topology
> > information to the guest in a safe manner. Enabling the feature
> > eliminates topology-related #VEs: the TDX module virtualizes
> > accesses to the CPUID leafs and the MSR.
> >
> > Enable ENUM_TOPOLOGY if it is available.
> 
> I cant find the ENUM_TOPOLOGY in ABI spec (https://cdrdv2.intel.com/v1/dl/getContent/795381).
> 
> Can you point me to the correct document?

I guess JSON dump is out of sync with the PDF doc. See this:

https://cdrdv2.intel.com/v1/dl/getContent/733579

-- 
  Kiryl Shutsemau / Kirill A. Shutemov