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Re: [RFC PATCH] xen/design: Add design for EFI dom0less system start

Hi Luca,

On 07/09/2021 07:52, Luca Fancellu wrote:
Add a design describing a proposal to improve the EFI
configuration file, adding keywords to describe domU
guests and allowing to start a dom0less system.

Signed-off-by: Luca Fancellu <luca.fancellu@xxxxxxx>
  docs/designs/efi-arm-dom0less.md | 105 +++++++++++++++++++++++++++++++
  1 file changed, 105 insertions(+)
  create mode 100644 docs/designs/efi-arm-dom0less.md

diff --git a/docs/designs/efi-arm-dom0less.md b/docs/designs/efi-arm-dom0less.md
new file mode 100644
index 0000000000..8d8fa2243f
--- /dev/null
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@@ -0,0 +1,105 @@
+# Xen EFI configuration file
+The current configuration file used by Xen when it is started as an EFI
+application is considering only the dom0 guest and doesn't have any
+property to describe and load in memory domU guests.

From my understanding, the problem is less about properties (we already have them in the Device-Tree) but more about where are the binaries located in memory as we don't know in advance.

So I would like to propose something that build on top of the Device-Tree work we did. Note this is early thoughts.

The problematic nodes in the DT are:

        module@0x4a000000 {
            compatible = "multiboot,kernel", "multiboot,module";
            reg = <0x0 0x4a000000 0xffffff>;
            bootargs = "console=ttyAMA0 init=/bin/sh";

        module@0x4b000000 {
            compatible = "multiboot,ramdisk", "multiboot,module";
            reg = <0x0 0x4b000000 0xffffff>;

In particular the property "reg" cannot be known in advance because the UEFI stub will be responsible to load the binaries in memory.

What we could do is providing a list of binaries to load and associate a key for each of them. Something like:

binary=<binary> <key>
binary=<binary2> <key2>

We can then replace the property "reg" with a new property "uefi,key" that will contain the name of the binary.

What do you think?


Julien Grall



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