tdx: init APs with the ACPI mailbox protocol #970
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Mailbox
This is the implementation of #610, initialization of APs with an implementation of the ACPI Mailbox protocol, described in section 5.2.12.19 of the ACPI spec
Changes
Igvmfilegen
The TDX reset vector has been modified to spin on APs until the kernel writes a wakeup command to the mailbox page. The AP then jumps to the wakeup address written by the kernel.
Boot Shim
The kernel expects that APs are ready to be woken up via the wakeup command, meaning that the VPs must be spinning before we jump to the kernel. Starting VPs under a HyperV host VMM is done with hypercalls, but there is no existing method to invoke hypercalls from the shim when TDX-isolated.
In this PR, TDX-specific hypercall initialization and invocation flows are added to the shim.