[RFC PATCH v2 68/69] KVM: TDX: add document on TDX MODULE

[isaku . yamahata]

From: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>

Add a document on how to integrate TDX MODULE into initrd so that
TDX MODULE can be updated on kernel startup.

Signed-off-by: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
---
 Documentation/virt/kvm/tdx-module.rst | 48 +++++++++++++++++++++++++++
 1 file changed, 48 insertions(+)
 create mode 100644 Documentation/virt/kvm/tdx-module.rst

diff --git a/Documentation/virt/kvm/tdx-module.rst b/Documentation/virt/kvm/tdx-module.rst
new file mode 100644
index 000000000000..8beea8302f94
--- /dev/null
+++ b/Documentation/virt/kvm/tdx-module.rst
@@ -0,0 +1,48 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+==========
+TDX MODULE
+==========
+
+Integrating TDX MODULE into initrd
+==================================
+If TDX is enabled in KVM(CONFIG_KVM_INTEL_TDX=y), kernel is able to load
+tdx seam module from initrd.
+The related modules (seamldr.ac, libtdx.so and libtdx.so.sigstruct) need to be
+stored in initrd.
+
+tdx-seam is a sample hook script for initramfs-tools.
+TDXSEAM_SRCDIR are the directory in the host file system to store files related
+to TDX MODULE.
+
+Since it heavily depends on distro how to prepare initrd, here's a example how
+to prepare an initrd.
+(Actually this is taken from Documentation/x86/microcode.rst)
+::
+  #!/bin/bash
+
+  if [ -z "$1" ]; then
+      echo "You need to supply an initrd file"
+      exit 1
+  fi
+
+  INITRD="$1"
+
+  DSTDIR=lib/firmware/intel-seam
+  TMPDIR=/tmp/initrd
+  LIBTDX="/lib/firmware/intel-seam/seamldr.acm /lib/firmware/intel-seam/libtdx.so /lib/firmware/intel-seam/libtdx.so.sigstruct"
+
+  rm -rf $TMPDIR
+
+  mkdir $TMPDIR
+  cd $TMPDIR
+  mkdir -p $DSTDIR
+
+  cp ${LIBTDX} ${DSTDIR}
+
+  find . | cpio -o -H newc > ../tdx-seam.cpio
+  cd ..
+  mv $INITRD $INITRD.orig
+  cat tdx-seam.cpio $INITRD.orig > $INITRD
+
+  rm -rf $TMPDIR
-- 
2.25.1