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That way, the EFI stub can just invoke it if it exists, > and what happens under the hood as a result is entirely under the control of > the firmware. Let me try to explain and please ask if anything's not clear because this is a complex topic: When a SEV-SNP guest starts, a Secure VM Service Module running at VMPL0 (higher privilege level than the guest's) is executed first. That's a paravisor, see here for a possible explanation: https://ksayid.github.io/confidential-computing-notes/docs/core/paravisor/. That paravisor will boot OVMF, and then OVMF will boot the guest kernel. The SVSM must know the Alternate Injection choice of the first component which is the OVMF, so it will be able to enable Alternate Injection in the guest VMSA and record OVMF's registration. The guest kernel should be able to make its own independent decision about whether to use Alternate Injection or not. If the kernel wants it, the kernel must register itself — this registration is performed in guest kernel code so that it remains under the guest kernel's control. The guest kernel needs to register Alternate Injection before ExitBootServices() so the SVSM registration counter always reflects the correct, current state of Alternate Injection across the OVMF-to-kernel hand-off. But if we leave the OVMF to decide for the guest kernel, that is violating the confidential computing principles of the guest being in control. I hope this makes more sense. Thanks, Melody.