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Date:   Tue, 29 Mar 2022 10:52:34 -0700
From:   Isaku Yamahata <isaku.yamahata@gmail.com>
To:     "Tian, Kevin" <kevin.tian@intel.com>
Cc:     "Huang, Kai" <kai.huang@intel.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        "Hansen, Dave" <dave.hansen@intel.com>,
        "Christopherson,, Sean" <seanjc@google.com>,
        "pbonzini@redhat.com" <pbonzini@redhat.com>,
        "kirill.shutemov@linux.intel.com" <kirill.shutemov@linux.intel.com>,
        "sathyanarayanan.kuppuswamy@linux.intel.com" 
        <sathyanarayanan.kuppuswamy@linux.intel.com>,
        "peterz@infradead.org" <peterz@infradead.org>,
        "Luck, Tony" <tony.luck@intel.com>,
        "ak@linux.intel.com" <ak@linux.intel.com>,
        "Williams, Dan J" <dan.j.williams@intel.com>,
        "Yamahata, Isaku" <isaku.yamahata@intel.com>,
        isaku.yamahata@gmail.com
Subject: Re: [PATCH v2 01/21] x86/virt/tdx: Detect SEAM
Message-ID: <20220329175234.GA1915371@ls.amr.corp.intel.com>
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On Mon, Mar 28, 2022 at 08:10:47AM +0000,
"Tian, Kevin" <kevin.tian@intel.com> wrote:

> > From: Huang, Kai <kai.huang@intel.com>
> > Sent: Monday, March 28, 2022 11:55 AM
> >
> > SEAMRR and TDX KeyIDs are configured by BIOS and they are static during
> > machine's runtime.  On the other hand, TDX module can be updated and
> > reinitialized at runtime (not supported in this series but will be supported in
> > the future).  Theoretically, even P-SEAMLDR can be updated at runtime
> > (although
> > I think unlikely to be supported in Linux).  Therefore I think detecting
> > SEAMRR
> > and TDX KeyIDs at boot fits better.
> 
> If those info are static it's perfectly fine to detect them until they are
> required... and following are not solid cases (e.g. just exposing SEAM
> alone doesn't tell the availability of TDX) but let's also hear the opinions
> from others.

One use case is cloud use case.  If TDX module is initialized dynamically at
runtime, cloud management system wants to know if the physical machine is
capable of TDX in addition to if TDX module is initialized.  Also how many TDs
can be run on the machine even when TDX module is not initialized yet.  The
management system will schedule TDs based on those information.
-- 
Isaku Yamahata <isaku.yamahata@gmail.com>