The upcoming new Idle HLT Intercept feature allows for the HLT instruction execution by a vCPU to be intercepted by the hypervisor only if there are no pending V_INTR and V_NMI events for the vCPU. When the vCPU is expected to service the pending V_INTR and V_NMI events, the Idle HLT intercept won’t trigger. The feature allows the hypervisor to determine if the vCPU is actually idle and reduces wasteful VMEXITs.
Presence of the Idle HLT Intercept feature is indicated via CPUID function Fn8000_000A_EDX[30].
Document for the Idle HLT intercept feature is available at [1].
[1]: AMD64 Architecture Programmer's Manual Pub. 24593, April 2024, Vol 2, 15.9 Instruction Intercepts (Table 15-7: IDLE_HLT). https://bugzilla.kernel.org/attachment.cgi?id=306250
Testing Done: Added a selftest to test the Idle HLT intercept functionality. Tested SEV and SEV-ES guest for the Idle HLT intercept functionality.
v1 -> v2 - Done changes in svm_idle_hlt_test based on the review comments from Sean. - Added an enum based approach to get binary stats in vcpu_get_stat() which doesn't use string to get stat data based on the comments from Sean. - Added self_halt() and cli() helpers based on the comments from Sean.
Manali Shukla (5): x86/cpufeatures: Add CPUID feature bit for Idle HLT intercept KVM: SVM: Add Idle HLT intercept support KVM: selftests: Add safe_halt() and cli() helpers to common code KVM: selftests: Add an interface to read the data of named vcpu stat KVM: selftests: KVM: SVM: Add Idle HLT intercept test
arch/x86/include/asm/cpufeatures.h | 1 + arch/x86/include/asm/svm.h | 1 + arch/x86/include/uapi/asm/svm.h | 2 + arch/x86/kvm/svm/svm.c | 15 +++- tools/testing/selftests/kvm/Makefile | 1 + .../testing/selftests/kvm/include/kvm_util.h | 66 ++++++++++++++ .../selftests/kvm/include/x86_64/processor.h | 18 ++++ tools/testing/selftests/kvm/lib/kvm_util.c | 32 +++++++ .../selftests/kvm/x86_64/svm_idle_hlt_test.c | 87 +++++++++++++++++++ 9 files changed, 220 insertions(+), 3 deletions(-) create mode 100644 tools/testing/selftests/kvm/x86_64/svm_idle_hlt_test.c
base-commit: 2489e6c9ebb57d6d0e98936479b5f586201379c7