linux-kernel - Re: [PATCH v7 04/20] x86/virt/tdx: Add skeleton to initialize TDX on demand

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Date:   Wed, 23 Nov 2022 21:58:37 +0000
From:   "Huang, Kai" <kai.huang@...el.com>
To:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     "Luck, Tony" <tony.luck@...el.com>,
        "bagasdotme@...il.com" <bagasdotme@...il.com>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>,
        "Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "Chatre, Reinette" <reinette.chatre@...el.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "Yamahata, Isaku" <isaku.yamahata@...el.com>,
        "Shahar, Sagi" <sagis@...gle.com>,
        "imammedo@...hat.com" <imammedo@...hat.com>,
        "Gao, Chao" <chao.gao@...el.com>,
        "Brown, Len" <len.brown@...el.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "sathyanarayanan.kuppuswamy@...ux.intel.com" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        "Huang, Ying" <ying.huang@...el.com>,
        "Williams, Dan J" <dan.j.williams@...el.com>
Subject: Re: [PATCH v7 04/20] x86/virt/tdx: Add skeleton to initialize TDX on
 demand

On Wed, 2022-11-23 at 08:58 -0800, Dave Hansen wrote:
> On 11/23/22 02:18, Huang, Kai wrote:
> > > Again, there are a lot of words in that comment, but I'm not sure why
> > > it's here.  Despite all the whinging about ACPI, doesn't it boil down to:
> > > 
> > >       The TDX module itself establishes its own concept of how many
> > >       logical CPUs there are in the system when it is loaded.
> > > 
> > This isn't accurate.  TDX MCHECK records the total number of logical CPUs when
> > the BIOS enables TDX.  This happens before the TDX module is loaded.  In fact
> > the TDX module only gets this information from a secret location.
> 
> Kai, this is the point where I lose patience with the conversation
> around this series.  I'll you paste you the line of code where the TDX
> module literally "establishes its own concept of how many logical CPUs
> there are in the system":
> 
> >     //NUM_LPS
> >     tdx_global_data_ptr->num_of_lps = sysinfo_table_ptr->mcheck_fields.tot_num_lps;
> 
> Yes, this is derived directly from MCHECK.  But, this concept is
> separate from MCHECK.  We have seen zero actual facts from you or other
> folks at Intel that this is anything other than an arbitrary choice made
> for the convenience of the TDX module.  It _might_ not be this way.  I'm
> open to hearing those facts and changing my position on this.
> 
> But, please bring facts, not random references to "secret locations"
> that aren't that secret.

Agreed.  Thanks for providing the comment and will use it.