From: Manali Shukla Manali.Shukla@amd.com
Execution of the HLT instruction by a vCPU can be intercepted by the hypervisor by setting the HLT-Intercept Bit in VMCB, thus resulting in a VMEXIT. It can be possible that soon after the VMEXIT, hypervisor observes that there are pending V_INTR and V_NMI events for the vCPU and causes it to perform a VMRUN to service those events. In that case VMEXIT is wasteful.
The Idle HLT intercept feature allows for the HLT instruction execution by a vCPU to be intercepted by hypervisor only if there are no pending V_INTR and V_NMI events for the vCPU. The Idle HLT intercept will not be triggerred, when vCPU is expected to have pending events (V_INR and V_NMI).
The feature allows the hypervisor to determine whether vCPU is idle and reduces wasteful VMEXITs.
Details about Idle HLT intercept can be found in AMD APM [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
Signed-off-by: Manali Shukla Manali.Shukla@amd.com --- arch/x86/include/asm/svm.h | 1 + arch/x86/include/uapi/asm/svm.h | 2 ++ arch/x86/kvm/svm/svm.c | 11 ++++++++--- 3 files changed, 11 insertions(+), 3 deletions(-)
diff --git a/arch/x86/include/asm/svm.h b/arch/x86/include/asm/svm.h index 728c98175b9c..3a91928a4060 100644 --- a/arch/x86/include/asm/svm.h +++ b/arch/x86/include/asm/svm.h @@ -116,6 +116,7 @@ enum { INTERCEPT_INVPCID, INTERCEPT_MCOMMIT, INTERCEPT_TLBSYNC, + INTERCEPT_IDLE_HLT = 166, };
diff --git a/arch/x86/include/uapi/asm/svm.h b/arch/x86/include/uapi/asm/svm.h index 80e1df482337..9910f86a2cef 100644 --- a/arch/x86/include/uapi/asm/svm.h +++ b/arch/x86/include/uapi/asm/svm.h @@ -95,6 +95,7 @@ #define SVM_EXIT_CR14_WRITE_TRAP 0x09e #define SVM_EXIT_CR15_WRITE_TRAP 0x09f #define SVM_EXIT_INVPCID 0x0a2 +#define SVM_EXIT_IDLE_HLT 0x0a6 #define SVM_EXIT_NPF 0x400 #define SVM_EXIT_AVIC_INCOMPLETE_IPI 0x401 #define SVM_EXIT_AVIC_UNACCELERATED_ACCESS 0x402 @@ -223,6 +224,7 @@ { SVM_EXIT_CR4_WRITE_TRAP, "write_cr4_trap" }, \ { SVM_EXIT_CR8_WRITE_TRAP, "write_cr8_trap" }, \ { SVM_EXIT_INVPCID, "invpcid" }, \ + { SVM_EXIT_IDLE_HLT, "idle-halt" }, \ { SVM_EXIT_NPF, "npf" }, \ { SVM_EXIT_AVIC_INCOMPLETE_IPI, "avic_incomplete_ipi" }, \ { SVM_EXIT_AVIC_UNACCELERATED_ACCESS, "avic_unaccelerated_access" }, \ diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c index 0f3b59da0d4a..223c670bf986 100644 --- a/arch/x86/kvm/svm/svm.c +++ b/arch/x86/kvm/svm/svm.c @@ -1289,8 +1289,12 @@ static void init_vmcb(struct kvm_vcpu *vcpu) svm_set_intercept(svm, INTERCEPT_MWAIT); }
- if (!kvm_hlt_in_guest(vcpu->kvm)) - svm_set_intercept(svm, INTERCEPT_HLT); + if (!kvm_hlt_in_guest(vcpu->kvm)) { + if (cpu_feature_enabled(X86_FEATURE_IDLE_HLT)) + svm_set_intercept(svm, INTERCEPT_IDLE_HLT); + else + svm_set_intercept(svm, INTERCEPT_HLT); + }
control->iopm_base_pa = __sme_set(iopm_base); control->msrpm_base_pa = __sme_set(__pa(svm->msrpm)); @@ -3291,6 +3295,7 @@ static int (*const svm_exit_handlers[])(struct kvm_vcpu *vcpu) = { [SVM_EXIT_CR4_WRITE_TRAP] = cr_trap, [SVM_EXIT_CR8_WRITE_TRAP] = cr_trap, [SVM_EXIT_INVPCID] = invpcid_interception, + [SVM_EXIT_IDLE_HLT] = kvm_emulate_halt, [SVM_EXIT_NPF] = npf_interception, [SVM_EXIT_RSM] = rsm_interception, [SVM_EXIT_AVIC_INCOMPLETE_IPI] = avic_incomplete_ipi_interception, @@ -3453,7 +3458,7 @@ int svm_invoke_exit_handler(struct kvm_vcpu *vcpu, u64 exit_code) return interrupt_window_interception(vcpu); else if (exit_code == SVM_EXIT_INTR) return intr_interception(vcpu); - else if (exit_code == SVM_EXIT_HLT) + else if (exit_code == SVM_EXIT_HLT || exit_code == SVM_EXIT_IDLE_HLT) return kvm_emulate_halt(vcpu); else if (exit_code == SVM_EXIT_NPF) return npf_interception(vcpu);