KVM: x86: ioapic: Optimize EOI handling to reduce unnecessary VM exits

Commit Message

weizijie Nov. 21, 2024, 6:50 a.m. UTC

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 the vector that is pending at
the time of injection. Then, upon the next guest exit, clean up the
ioapic_handled_vectors corresponding to the vector number that was
pending. This ensures that interrupts are properly handled and prevents
performance issues.

Signed-off-by: weizijie <[e-mail]>
Signed-off-by: xuyun <[e-mail]>
---
 arch/x86/include/asm/kvm_host.h |  1 +
 arch/x86/kvm/ioapic.c           | 11 +++++++++--
 arch/x86/kvm/vmx/vmx.c          | 10 ++++++++++
 3 files changed, 20 insertions(+), 2 deletions(-)

Patch

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index e159e44a6a1b..b008c933d2ab 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
+	DECLARE_BITMAP(ioapic_pending_vectors, 256);
 };
 
 struct kvm_lpage_info {
diff --git a/arch/x86/kvm/ioapic.c b/arch/x86/kvm/ioapic.c
index 995eb5054360..6f5a88dc63da 100644
--- a/arch/x86/kvm/ioapic.c
+++ b/arch/x86/kvm/ioapic.c
@@ -284,6 +284,8 @@  void kvm_ioapic_scan_entry(struct kvm_vcpu *vcpu, ulong *ioapic_handled_vectors)
 
 	spin_lock(&ioapic->lock);
 
+	bitmap_zero(vcpu->arch.ioapic_pending_vectors, 256);
+
 	/* Make sure we see any missing RTC EOI */
 	if (test_bit(vcpu->vcpu_id, dest_map->map))
 		__set_bit(dest_map->vectors[vcpu->vcpu_id],
@@ -297,10 +299,15 @@  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);
+				__set_bit(e->fields.vector,
+					  vcpu->arch.ioapic_pending_vectors);
+			}
 		}
 	}
 	spin_unlock(&ioapic->lock);
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 0f008f5ef6f0..572e6f9b8602 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -5710,6 +5710,16 @@  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 the
+	 * corresponding bit after the interrupt is completed.
+	 */
+	if (test_bit(vector, vcpu->arch.ioapic_pending_vectors)) {
+		clear_bit(vector, vcpu->arch.ioapic_pending_vectors);
+		clear_bit(vector, vcpu->arch.ioapic_handled_vectors);
+		kvm_make_request(KVM_REQ_LOAD_EOI_EXITMAP, vcpu);
+	}
 	return 1;
 }