From patchwork Mon Mar 3 05:22:25 2025 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: weizijie X-Patchwork-Id: 13998204 Received: from out30-133.freemail.mail.aliyun.com (out30-133.freemail.mail.aliyun.com [115.124.30.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D4C6323F383; Mon, 3 Mar 2025 05:28:06 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.133 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740979691; cv=none; b=RWzSFpvhkNcPSwWyGkM7Wsfew+WBg4afR8FCwdFm+yCmGFoz772dTSVVaWstULIMYSXV03NJHd33MxTHOio55GCVCgG9DAaoB5ydFGFb7EL/tnh9zgme9t5LlezDBmIEnQcs9bAuPv0acmFbRKSSUgpfL1WiAbunM3YUoutbEJ4= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740979691; c=relaxed/simple; bh=3SGXOIf3Drc5jxLCFLqX3ju8XNaEf0lpwJGlHy9oFgE=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=E9DlfW/a7U7ybD8sO/dCp4ExS6AUXxcKZpHaMu1PSM8X8DPPpsWtlUEVD5kqhA17GKZEVUMUJ/KmEmQbHemd2/TbqaiPsi/5ZvhtmArMQ7Tte5upwKnff5SE0IXDDe4qyPSNrtd6xJzYafn94lF7NXbqFn3Z2lasvMAtGtaMsGs= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com; spf=pass smtp.mailfrom=linux.alibaba.com; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b=DUbqN4f8; arc=none smtp.client-ip=115.124.30.133 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b="DUbqN4f8" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1740979684; h=From:To:Subject:Date:Message-ID:MIME-Version:Content-Type; bh=wKW2qNL0GYKBXb+KdJ8WKvFoPhdHKIW6tOAlWFUGX9g=; b=DUbqN4f8Y8WV5NeA3MjCaZmo2kp7pIerNdnusjIcBT/j3rNumnAU6ADbZqsfkw+8RUx/peru/lubr/zgIlttebwhhVJc4IAxcwwZM7nphW8US3+TrnjU3hCSWg4hC/tI+cgeBikqsfWeEpSeZs/NUlG6VGC1ovcxCtXdy6e0DP0= Received: from localhost(mailfrom:zijie.wei@linux.alibaba.com fp:SMTPD_---0WQYk3HY_1740979359 cluster:ay36) by smtp.aliyun-inc.com; Mon, 03 Mar 2025 13:22:43 +0800 From: weizijie To: Sean Christopherson , kai.huang@intel.com, Paolo Bonzini , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H . Peter Anvin" , kvm@vger.kernel.org, linux-kernel@vger.kernel.org Cc: weizijie , xuyun Subject: [PATCH v4] KVM: x86: ioapic: Optimize EOI handling to reduce unnecessary VM exits Date: Mon, 3 Mar 2025 13:22:25 +0800 Message-ID: <20250303052227.523411-1-zijie.wei@linux.alibaba.com> X-Mailer: git-send-email 2.43.5 In-Reply-To: <20241121065039.183716-1-zijie.wei@linux.alibaba.com> References: <20241121065039.183716-1-zijie.wei@linux.alibaba.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Configuring IOAPIC routed interrupts triggers KVM to rescan all vCPU's ioapic_handled_vectors which is used to control which vectors need to trigger EOI-induced VMEXITs. If any interrupt is already in service on some vCPU using some vector when the IOAPIC is being rescanned, the vector is set to vCPU's ioapic_handled_vectors. If the vector is then reused by other interrupts, each of them will cause a VMEXIT even it is unnecessary. W/o further IOAPIC rescan, the vector remains set, and this issue persists, impacting guest's interrupt performance. Both commit db2bdcbbbd32 ("KVM: x86: fix edge EOI and IOAPIC reconfig race") and commit 0fc5a36dd6b3 ("KVM: x86: ioapic: Fix level-triggered EOI and IOAPIC reconfigure race") mentioned this issue, but it was considered as "rare" thus was not addressed. However in real environment this issue can actually happen in a well-behaved guest. 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 bits in the eoi_exit_bitmap are cleared, avoiding unnecessary VM exits. Co-developed-by: xuyun Signed-off-by: xuyun Signed-off-by: weizijie Reviewed-by: Kai Huang --- arch/x86/include/asm/kvm_host.h | 1 + arch/x86/kvm/ioapic.c | 10 ++++++++-- arch/x86/kvm/irq_comm.c | 9 +++++++-- arch/x86/kvm/lapic.c | 13 +++++++++++++ 4 files changed, 29 insertions(+), 4 deletions(-) diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index 0b7af5902ff7..8c50e7b4a96f 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -1062,6 +1062,7 @@ 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/lapic.c b/arch/x86/kvm/lapic.c index a009c94c26c2..7c540a0eb340 100644 --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -1466,6 +1466,19 @@ static void kvm_ioapic_send_eoi(struct kvm_lapic *apic, int vector) if (!kvm_ioapic_handles_vector(apic, vector)) return; + /* + * 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. + * This ensures the vector is cleared in the vCPU's ioapic_handled_vectors, + * if the vector is reused by non-IOAPIC interrupts, avoiding unnecessary + * EOI-induced VMEXITs for that vector. + */ + if (apic->vcpu->arch.last_pending_vector == vector) { + apic->vcpu->arch.last_pending_vector = 0; + kvm_make_request(KVM_REQ_SCAN_IOAPIC, apic->vcpu); + } + /* Request a KVM exit to inform the userspace IOAPIC. */ if (irqchip_split(apic->vcpu->kvm)) { apic->vcpu->arch.pending_ioapic_eoi = vector;