RFC Alternate Injection: Secure Interrupt Delivery for SEV-SNP Guests

This patchset introduces host-side KVM support for AMD SEV-SNP Alternate Injection, providing secure interrupt delivery for confidential guests against malicious or untrusted hypervisor injection attacks.

Background & Motivation
-----------------------
In standard SEV-SNP deployments, retaining hypervisor-controlled interrupt injection leaves confidential VMs vulnerable to unexpected or malformed interrupt sequences. Alternate Injection mitigates this by shifting interrupt injection control into the guest security realm. It builds on top of Restricted Injection, leveraging the established secure communication channel to interact with a Secure VM Service Module (SVSM) that handles APIC emulation.

Series Status & Dependencies
----------------------------
- This is an RFC patchset intended for early architectural feedback.
- Rebased on commit 6efc8ea4653f8bfd4d59ea5fa9589d028e037909 (joro/kvm-planes-v7.1).
- Tested against:
* Latest SVSM build
* SEV-SNP guest kernel (rebased to latest, with Alternate Injection)
* EDK2 (rebased to latest, with Alternate Injection support)
* QEMU commit 8db5273ca97f26043f64d1390f906e434c675db2

    (HEAD -> qemu-planes-linux-v7.1, joerg/qemu-planes-linux-v7.1)

Next Steps & Discussion
-----------------------
An alternative design approach has also been explored and will be presented at KVM Forum 2026 in the talk:
"COCONUT-SVSM, KVM Planes, and Secure Interrupt Injection - Upstream Alignment" [1].

Welcome review and comments on this RFC series.

Plan to refine and update the patches further following feedback gathered at KVM Forum.

[1] https://pretalx.com/kvm-forum-2026/talk/ZB3GWA/

Thanks,
Melody

Melody Wang (9):
x86/sev: Define extended #HV doorbell page structure
KVM: SVM: Add support for Alternate Injection for the SEV-SNP #HV
doorbell page NAE event
KVM: SVM: Add Alternate Injection support
KVM: SVM: Add Alternate Injection path
KVM: SVM: Bypass lapic for VMPL1-3 guest with Alternate Injection
enabled
KVM: SVM: Inject #HV into VMPL0 with Alternate Injection enabled
KVM: SVM: Notify the SVSM an intercept happened during interrupt
delivery
KVM: SVM: Clear AVIC Enable when Alternate Injection is enabled
KVM: SVM: Enable Alternate Injection for an SEV-SNP guest

 arch/x86/include/asm/cpufeatures.h |   1 +
 arch/x86/include/asm/kvm-x86-ops.h |   2 +
 arch/x86/include/asm/kvm_host.h    |   2 +
 arch/x86/include/asm/sev-common.h  |   1 +
 arch/x86/include/asm/svm.h         |  60 ++++-
 arch/x86/include/uapi/asm/svm.h    |   2 +
 arch/x86/kvm/irq.c                 |   4 +
 arch/x86/kvm/lapic.c               |  10 +-
 arch/x86/kvm/lapic.h               |   1 +
 arch/x86/kvm/svm/sev.c             | 371 ++++++++++++++++++++++++++++-
 arch/x86/kvm/svm/svm.c             |  66 ++++-
 arch/x86/kvm/svm/svm.h             |  30 +++
 12 files changed, 531 insertions(+), 19 deletions(-)

2.43.0