[PATCHv5 0/8] Virtual NMI feature

Santosh Shukla
2022-10-27T08:39:01Z

VNMI Spec is at [1].

Change History:

v5 (6.1-rc2)
01,02,06 - Renamed s/X86_FEATURE_V_NMI/X86_FEATURE_AMD_VNMI (Jim Mattson)

v4 (v6.0-rc3):
https://lore.kernel.org/all/20220829100850.1474-1-santosh.shukla@amd.com/

v3 (rebased on eb555cb5b794f):
https://lore.kernel.org/all/20220810061226.1286-1-santosh.shukla@amd.com/

v2:
https://lore.kernel.org/lkml/20220709134230.2397-7-santosh.shukla@amd.com/T/#m4bf8a131748688fed00ab0fefdcac209a169e202

v1:
https://lore.kernel.org/all/20220602142620.3196-1-santosh.shukla@amd.com/

Description:
Currently, NMI is delivered to the guest using the Event Injection
mechanism [2]. 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.

If NMI virtualization enabled and NMI_INTERCEPT bit is unset
then HW will exit with #INVALID exit reason.

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
* tested with vGIF enable and disable.
* tested nested env:
- L1+L2 using vnmi
- L1 using vnmi and L2 not

Thanks,
Santosh
[1] https://www.amd.com/en/support/tech-docs/amd64-architecture-programmers-manual-volumes-1-5
(Ch-15.21.10 - NMI Virtualization)

[2] https://www.amd.com/en/support/tech-docs/amd64-architecture-programmers-manual-volumes-1-5
(Ch-15.20 - Event Injection)

Santosh Shukla (8):
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: nSVM: emulate VMEXIT_INVALID case for 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 | 32 ++++++++++++++
arch/x86/kvm/svm/svm.c | 44 ++++++++++++++++++-
arch/x86/kvm/svm/svm.h | 68 ++++++++++++++++++++++++++++++
5 files changed, 151 insertions(+), 1 deletion(-)

--
2.25.1