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Date:   Fri, 9 Jun 2023 01:40:56 +0300
From:   kirill.shutemov@linux.intel.com
To:     Kai Huang <kai.huang@intel.com>
Cc:     linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        linux-mm@kvack.org, dave.hansen@intel.com, tony.luck@intel.com,
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        sathyanarayanan.kuppuswamy@linux.intel.com, bagasdotme@gmail.com,
        sagis@google.com, imammedo@redhat.com
Subject: Re: [PATCH v11 09/20] x86/virt/tdx: Use all system memory when
 initializing TDX module as TDX memory
Message-ID: <20230608224056.2j524gnkrdjtirti@box>
References: <cover.1685887183.git.kai.huang@intel.com>
 <468533166590ff5ed11730350c4af8cdb0b99165.1685887183.git.kai.huang@intel.com>
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On Mon, Jun 05, 2023 at 02:27:22AM +1200, Kai Huang wrote:
> As a step of initializing the TDX module, the kernel needs to tell the
> TDX module which memory regions can be used by the TDX module as TDX
> guest memory.
> 
> TDX reports a list of "Convertible Memory Region" (CMR) to tell the
> kernel which memory is TDX compatible.  The kernel needs to build a list
> of memory regions (out of CMRs) as "TDX-usable" memory and pass them to
> the TDX module.  Once this is done, those "TDX-usable" memory regions
> are fixed during module's lifetime.
> 
> To keep things simple, assume that all TDX-protected memory will come
> from the page allocator.  Make sure all pages in the page allocator
> *are* TDX-usable memory.
> 
> As TDX-usable memory is a fixed configuration, take a snapshot of the
> memory configuration from memblocks at the time of module initialization
> (memblocks are modified on memory hotplug).  This snapshot is used to
> enable TDX support for *this* memory configuration only.  Use a memory
> hotplug notifier to ensure that no other RAM can be added outside of
> this configuration.
> 
> This approach requires all memblock memory regions at the time of module
> initialization to be TDX convertible memory to work, otherwise module
> initialization will fail in a later SEAMCALL when passing those regions
> to the module.  This approach works when all boot-time "system RAM" is
> TDX convertible memory, and no non-TDX-convertible memory is hot-added
> to the core-mm before module initialization.
> 
> For instance, on the first generation of TDX machines, both CXL memory
> and NVDIMM are not TDX convertible memory.  Using kmem driver to hot-add
> any CXL memory or NVDIMM to the core-mm before module initialization
> will result in failure to initialize the module.  The SEAMCALL error
> code will be available in the dmesg to help user to understand the
> failure.
> 
> Signed-off-by: Kai Huang <kai.huang@intel.com>
> Reviewed-by: "Huang, Ying" <ying.huang@intel.com>
> Reviewed-by: Isaku Yamahata <isaku.yamahata@intel.com>

Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>

-- 
  Kiryl Shutsemau / Kirill A. Shutemov