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Message-ID: <20240802195120.325560-6-seanjc@google.com>
Date: Fri, 2 Aug 2024 12:51:20 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 5/5] KVM: x86: Add fastpath handling of HLT VM-Exits
Add a fastpath for HLT VM-Exits by immediately re-entering the guest if
it has a pending wake event. When virtual interrupt delivery is enabled,
i.e. when KVM doesn't need to manually inject interrupts, this allows KVM
to stay in the fastpath run loop when a vIRQ arrives between the guest
doing CLI and STI;HLT. Without AMD's Idle HLT-intercept support, the CPU
generates a HLT VM-Exit even though KVM will immediately resume the guest.
Note, on bare metal, it's relatively uncommon for a modern guest kernel to
actually trigger this scenario, as the window between the guest checking
for a wake event and committing to HLT is quite small. But in a nested
environment, the timings change significantly, e.g. rudimentary testing
showed that ~50% of HLT exits where HLT-polling was successful would be
serviced by this fastpath, i.e. ~50% of the time that a nested vCPU gets
a wake event before KVM schedules out the vCPU, the wake event was pending
even before the VM-Exit.
Link: https://lore.kernel.org/all/20240528041926.3989-3-manali.shukla@amd.com
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
arch/x86/kvm/svm/svm.c | 13 +++++++++++--
arch/x86/kvm/vmx/vmx.c | 2 ++
arch/x86/kvm/x86.c | 23 ++++++++++++++++++++++-
arch/x86/kvm/x86.h | 1 +
4 files changed, 36 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index c115d26844f7..64381ff63034 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -4144,12 +4144,21 @@ static int svm_vcpu_pre_run(struct kvm_vcpu *vcpu)
static fastpath_t svm_exit_handlers_fastpath(struct kvm_vcpu *vcpu)
{
+ struct vcpu_svm *svm = to_svm(vcpu);
+
if (is_guest_mode(vcpu))
return EXIT_FASTPATH_NONE;
- if (to_svm(vcpu)->vmcb->control.exit_code == SVM_EXIT_MSR &&
- to_svm(vcpu)->vmcb->control.exit_info_1)
+ switch (svm->vmcb->control.exit_code) {
+ case SVM_EXIT_MSR:
+ if (!svm->vmcb->control.exit_info_1)
+ break;
return handle_fastpath_set_msr_irqoff(vcpu);
+ case SVM_EXIT_HLT:
+ return handle_fastpath_hlt(vcpu);
+ default:
+ break;
+ }
return EXIT_FASTPATH_NONE;
}
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index f18c2d8c7476..f6382750fbf0 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -7265,6 +7265,8 @@ static fastpath_t vmx_exit_handlers_fastpath(struct kvm_vcpu *vcpu,
return handle_fastpath_set_msr_irqoff(vcpu);
case EXIT_REASON_PREEMPTION_TIMER:
return handle_fastpath_preemption_timer(vcpu, force_immediate_exit);
+ case EXIT_REASON_HLT:
+ return handle_fastpath_hlt(vcpu);
default:
return EXIT_FASTPATH_NONE;
}
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 46686504cd47..eb5ea963698f 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -11373,7 +11373,10 @@ static int __kvm_emulate_halt(struct kvm_vcpu *vcpu, int state, int reason)
*/
++vcpu->stat.halt_exits;
if (lapic_in_kernel(vcpu)) {
- vcpu->arch.mp_state = state;
+ if (kvm_vcpu_has_events(vcpu))
+ vcpu->arch.pv.pv_unhalted = false;
+ else
+ vcpu->arch.mp_state = state;
return 1;
} else {
vcpu->run->exit_reason = reason;
@@ -11398,6 +11401,24 @@ int kvm_emulate_halt(struct kvm_vcpu *vcpu)
}
EXPORT_SYMBOL_GPL(kvm_emulate_halt);
+fastpath_t handle_fastpath_hlt(struct kvm_vcpu *vcpu)
+{
+ int ret;
+
+ kvm_vcpu_srcu_read_lock(vcpu);
+ ret = kvm_emulate_halt(vcpu);
+ kvm_vcpu_srcu_read_unlock(vcpu);
+
+ if (!ret)
+ return EXIT_FASTPATH_EXIT_USERSPACE;
+
+ if (kvm_vcpu_running(vcpu))
+ return EXIT_FASTPATH_REENTER_GUEST;
+
+ return EXIT_FASTPATH_EXIT_HANDLED;
+}
+EXPORT_SYMBOL_GPL(handle_fastpath_hlt);
+
int kvm_emulate_ap_reset_hold(struct kvm_vcpu *vcpu)
{
int ret = kvm_skip_emulated_instruction(vcpu);
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index 50596f6f8320..5185ab76fdd2 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -334,6 +334,7 @@ int x86_decode_emulated_instruction(struct kvm_vcpu *vcpu, int emulation_type,
int x86_emulate_instruction(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
int emulation_type, void *insn, int insn_len);
fastpath_t handle_fastpath_set_msr_irqoff(struct kvm_vcpu *vcpu);
+fastpath_t handle_fastpath_hlt(struct kvm_vcpu *vcpu);
extern struct kvm_caps kvm_caps;
extern struct kvm_host_values kvm_host;
--
2.46.0.rc2.264.g509ed76dc8-goog
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