[PATCH 0/7] Virtual NMI feature

From: Santosh Shukla
Date: Thu Jun 02 2022 - 10:26:45 EST


Currently, NMI is delivered to the guest using the Event Injection
mechanism [1]. The Event Injection mechanism does not block the delivery
of subsequent NMIs. So the Hypervisor needs to track the NMI delivery
and its completion(by intercepting IRET) before sending a new NMI.

Virtual NMI (VNMI) allows the hypervisor to inject the NMI into the guest
w/o using Event Injection mechanism meaning not required to track the
guest NMI and intercepting the IRET. To achieve that,
VNMI feature provides virtualized NMI and NMI_MASK capability bits in
VMCB intr_control -
V_NMI(11) - Indicates whether a virtual NMI is pending in the guest.
V_NMI_MASK(12) - Indicates whether virtual NMI is masked in the guest.
V_NMI_ENABLE(26) - Enables the NMI virtualization feature for the guest.

When Hypervisor wants to inject NMI, it will set V_NMI bit, Processor will
clear the V_NMI bit and Set the V_NMI_MASK which means the Guest is
handling NMI, After the guest handled the NMI, The processor will clear
the V_NMI_MASK on the successful completion of IRET instruction
Or if VMEXIT occurs while delivering the virtual NMI.

To enable the VNMI capability, Hypervisor need to program
V_NMI_ENABLE bit 1.

The presence of this feature is indicated via the CPUID function
0x8000000A_EDX[25].

Testing -
* Used qemu's `inject_nmi` for testing.
* tested with and w/o AVIC case.
* tested with kvm-unit-test

Thanks,
Santosh
[1] https://www.amd.com/system/files/TechDocs/40332.pdf - APM Vol2,
ch-15.20 - "Event Injection".

Santosh Shukla (7):
x86/cpu: Add CPUID feature bit for VNMI
KVM: SVM: Add VNMI bit definition
KVM: SVM: Add VNMI support in get/set_nmi_mask
KVM: SVM: Report NMI not allowed when Guest busy handling VNMI
KVM: SVM: Add VNMI support in inject_nmi
KVM: nSVM: implement nested VNMI
KVM: SVM: Enable VNMI feature

arch/x86/include/asm/cpufeatures.h | 1 +
arch/x86/include/asm/svm.h | 7 +++++
arch/x86/kvm/svm/nested.c | 8 +++++
arch/x86/kvm/svm/svm.c | 47 ++++++++++++++++++++++++++++--
arch/x86/kvm/svm/svm.h | 1 +
5 files changed, 62 insertions(+), 2 deletions(-)

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2.25.1