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Message-ID: <6b0980fc-74e7-3be5-c4a3-2583d6c26137@intel.com>
Date:   Wed, 30 Nov 2022 07:13:18 -0800
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Subject: Re: [PATCH v7 17/20] x86/virt/tdx: Configure global KeyID on all
 packages
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To:     "Huang, Kai" <kai.huang@intel.com>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "binbin.wu@linux.intel.com" <binbin.wu@linux.intel.com>
Cc:     "Luck, Tony" <tony.luck@intel.com>,
        "bagasdotme@gmail.com" <bagasdotme@gmail.com>,
        "ak@linux.intel.com" <ak@linux.intel.com>,
        "Wysocki, Rafael J" <rafael.j.wysocki@intel.com>,
        "kirill.shutemov@linux.intel.com" <kirill.shutemov@linux.intel.com>,
        "Christopherson,, Sean" <seanjc@google.com>,
        "Chatre, Reinette" <reinette.chatre@intel.com>,
        "pbonzini@redhat.com" <pbonzini@redhat.com>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "Yamahata, Isaku" <isaku.yamahata@intel.com>,
        "peterz@infradead.org" <peterz@infradead.org>,
        "Shahar, Sagi" <sagis@google.com>,
        "imammedo@redhat.com" <imammedo@redhat.com>,
        "Gao, Chao" <chao.gao@intel.com>,
        "Brown, Len" <len.brown@intel.com>,
        "sathyanarayanan.kuppuswamy@linux.intel.com" 
        <sathyanarayanan.kuppuswamy@linux.intel.com>,
        "Huang, Ying" <ying.huang@intel.com>,
        "Williams, Dan J" <dan.j.williams@intel.com>
References: <cover.1668988357.git.kai.huang@intel.com>
 <8d8285cc5efa6302cf42a3fe2c9153d1a9dbcdac.1668988357.git.kai.huang@intel.com>
 <a537b97b-0bdc-5bcc-9ce7-470f8fc1245b@linux.intel.com>
 <3d19683cdc13b7a3884f1e9e75743e922d4630f3.camel@intel.com>
From:   Dave Hansen <dave.hansen@intel.com>
In-Reply-To: <3d19683cdc13b7a3884f1e9e75743e922d4630f3.camel@intel.com>
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Precedence: bulk

On 11/30/22 00:34, Huang, Kai wrote:
> On Wed, 2022-11-30 at 11:35 +0800, Binbin Wu wrote:
>> On 11/21/2022 8:26 AM, Kai Huang wrote:
>>> After the array of TDMRs and the global KeyID are configured to the TDX
>>> module, use TDH.SYS.KEY.CONFIG to configure the key of the global KeyID
>>> on all packages.
>>>
>>> TDH.SYS.KEY.CONFIG must be done on one (any) cpu for each package.  And
>>> it cannot run concurrently on different CPUs.  Implement a helper to
>>> run SEAMCALL on one cpu for each package one by one, and use it to
>>> configure the global KeyID on all packages.
>>>
>>> Intel hardware doesn't guarantee cache coherency across different
>>> KeyIDs.  The kernel needs to flush PAMT's dirty cachelines (associated
>>> with KeyID 0) before the TDX module uses the global KeyID to access the
>>> PAMT.  Following the TDX module specification, flush cache before
>>> configuring the global KeyID on all packages.
>>>
>>> Given the PAMT size can be large (~1/256th of system RAM), just use
>>> WBINVD on all CPUs to flush.
>>>
>>> Note if any TDH.SYS.KEY.CONFIG fails, the TDX module may already have
>>> used the global KeyID to write any PAMT.  Therefore, need to use WBINVD
>>> to flush cache before freeing the PAMTs back to the kernel.  Note using
>>> MOVDIR64B (which changes the page's associated KeyID from the old TDX
>>> private KeyID back to KeyID 0, which is used by the kernel)
>>
>> It seems not accurate to say MOVDIR64B changes the page's associated KeyID.
>> It just uses the current KeyID for memory operations.
> 
> The "write" to the memory changes the page's associated KeyID to the KeyID that
> does the "write".  A more accurate expression perhaps should be MOVDIR64B +
> MFENSE, but I think it doesn't matter in changelog.

Just delete it from the changelog.  It's a distraction.  I'm not even
sure it's *necessary* to do any memory content conversion after the TDX
module has written gunk.

There won't be any integrity issues because integrity errors don't do
anything for KeyID-0 (no #MC).

I _think_ the reads of the page using KeyID-0 will see abort page
semantics.  That's *FINE*.