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Peter Anvin" , kvm@vger.kernel.org, linux-kernel@vger.kernel.org Cc: weizijie , xuyun Subject: [PATCH v2 Resend] KVM: x86: ioapic: Optimize EOI handling to reduce unnecessary VM exits Date: Thu, 20 Feb 2025 18:01:26 +0800 Message-ID: <20250220100126.299845-1-zijie.wei@linux.alibaba.com> X-Mailer: git-send-email 2.43.5 Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Address performance issues caused by a vector being reused by a non-IOAPIC source. commit 0fc5a36dd6b3 ("KVM: x86: ioapic: Fix level-triggered EOI and IOAPIC reconfigure race") addressed the issues related to EOI and IOAPIC reconfiguration races. However, it has introduced some performance concerns: Configuring IOAPIC interrupts while an interrupt request (IRQ) is already in service can unintentionally trigger a VM exit for other interrupts that normally do not require one, due to the settings of `ioapic_handled_vectors`. If the IOAPIC is not reconfigured during runtime, this issue persists, continuing to adversely affect performance. Simple Fix Proposal: A straightforward solution is to record highest in-service IRQ that is pending at the time of the last scan. Then, upon the next guest exit, do a full KVM_REQ_SCAN_IOAPIC. This ensures that a re-scan of the ioapic occurs only when the recorded vector is EOI'd, and subsequently, the extra bit in the eoi_exit_bitmap are cleared, avoiding unnecessary VM exits. Co-developed-by: xuyun Signed-off-by: xuyun Signed-off-by: weizijie --- arch/x86/include/asm/kvm_host.h | 1 + arch/x86/kvm/ioapic.c | 10 ++++++++-- arch/x86/kvm/irq_comm.c | 9 +++++++-- arch/x86/kvm/vmx/vmx.c | 9 +++++++++ 4 files changed, 25 insertions(+), 4 deletions(-) diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index e159e44a6a1b..f84a4881afa4 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -1041,6 +1041,7 @@ struct kvm_vcpu_arch { #if IS_ENABLED(CONFIG_HYPERV) hpa_t hv_root_tdp; #endif + u8 last_pending_vector; }; struct kvm_lpage_info { diff --git a/arch/x86/kvm/ioapic.c b/arch/x86/kvm/ioapic.c index 995eb5054360..40252a800897 100644 --- a/arch/x86/kvm/ioapic.c +++ b/arch/x86/kvm/ioapic.c @@ -297,10 +297,16 @@ void kvm_ioapic_scan_entry(struct kvm_vcpu *vcpu, ulong *ioapic_handled_vectors) u16 dm = kvm_lapic_irq_dest_mode(!!e->fields.dest_mode); if (kvm_apic_match_dest(vcpu, NULL, APIC_DEST_NOSHORT, - e->fields.dest_id, dm) || - kvm_apic_pending_eoi(vcpu, e->fields.vector)) + e->fields.dest_id, dm)) __set_bit(e->fields.vector, ioapic_handled_vectors); + else if (kvm_apic_pending_eoi(vcpu, e->fields.vector)) { + __set_bit(e->fields.vector, + ioapic_handled_vectors); + vcpu->arch.last_pending_vector = e->fields.vector > + vcpu->arch.last_pending_vector ? e->fields.vector : + vcpu->arch.last_pending_vector; + } } } spin_unlock(&ioapic->lock); diff --git a/arch/x86/kvm/irq_comm.c b/arch/x86/kvm/irq_comm.c index 8136695f7b96..1d23c52576e1 100644 --- a/arch/x86/kvm/irq_comm.c +++ b/arch/x86/kvm/irq_comm.c @@ -426,9 +426,14 @@ void kvm_scan_ioapic_routes(struct kvm_vcpu *vcpu, if (irq.trig_mode && (kvm_apic_match_dest(vcpu, NULL, APIC_DEST_NOSHORT, - irq.dest_id, irq.dest_mode) || - kvm_apic_pending_eoi(vcpu, irq.vector))) + irq.dest_id, irq.dest_mode))) __set_bit(irq.vector, ioapic_handled_vectors); + else if (kvm_apic_pending_eoi(vcpu, irq.vector)) { + __set_bit(irq.vector, ioapic_handled_vectors); + vcpu->arch.last_pending_vector = irq.vector > + vcpu->arch.last_pending_vector ? irq.vector : + vcpu->arch.last_pending_vector; + } } } srcu_read_unlock(&kvm->irq_srcu, idx); diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index 893366e53732..cd0db1496ce7 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -5702,6 +5702,15 @@ static int handle_apic_eoi_induced(struct kvm_vcpu *vcpu) /* EOI-induced VM exit is trap-like and thus no need to adjust IP */ kvm_apic_set_eoi_accelerated(vcpu, vector); + + /* When there are instances where ioapic_handled_vectors is + * set due to pending interrupts, clean up the record and do + * a full KVM_REQ_SCAN_IOAPIC. + */ + if (vcpu->arch.last_pending_vector == vector) { + vcpu->arch.last_pending_vector = 0; + kvm_make_request(KVM_REQ_SCAN_IOAPIC, vcpu); + } return 1; }