Re: [PATCH 3/3] KVM: x86: do not scan IRR twice on APICv vmentry

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On 2016/9/28 5:20, Paolo Bonzini wrote:
Calling apic_find_highest_irr results in IRR being scanned twice,
once in vmx_sync_pir_from_irr and once in apic_search_irr.  Change
vcpu_enter_guest to use sync_pir_from_irr (with a new argument to
trigger the RVI write), and let sync_pir_from_irr get the new RVI
directly from kvm_apic_update_irr.

Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
 arch/x86/include/asm/kvm_host.h |  2 +-
 arch/x86/kvm/lapic.c            | 25 ++++++++++++++++---------
 arch/x86/kvm/lapic.h            |  4 ++--
 arch/x86/kvm/svm.c              |  2 +-
 arch/x86/kvm/vmx.c              | 25 ++++++++++++++-----------
 arch/x86/kvm/x86.c              |  7 +++----
 6 files changed, 37 insertions(+), 28 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 4b20f7304b9c..f73eea243567 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -941,7 +941,7 @@ struct kvm_x86_ops {
 	void (*set_virtual_x2apic_mode)(struct kvm_vcpu *vcpu, bool set);
 	void (*set_apic_access_page_addr)(struct kvm_vcpu *vcpu, hpa_t hpa);
 	void (*deliver_posted_interrupt)(struct kvm_vcpu *vcpu, int vector);
-	void (*sync_pir_to_irr)(struct kvm_vcpu *vcpu);
+	void (*sync_pir_to_irr)(struct kvm_vcpu *vcpu, bool sync_rvi);
 	int (*set_tss_addr)(struct kvm *kvm, unsigned int addr);
 	int (*get_tdp_level)(void);
 	u64 (*get_mt_mask)(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio);
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index be8b7ad56dd1..85b79b90e3d0 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -317,7 +317,7 @@ static int find_highest_vector(void *bitmap)
 	     vec >= 0; vec -= APIC_VECTORS_PER_REG) {
 		reg = bitmap + REG_POS(vec);
 		if (*reg)
-			return fls(*reg) - 1 + vec;
+			return __fls(*reg) + vec;
 	}

 	return -1;
@@ -337,25 +337,32 @@ static u8 count_vectors(void *bitmap)
 	return count;
 }

-void __kvm_apic_update_irr(u32 *pir, void *regs)
+int __kvm_apic_update_irr(u32 *pir, void *regs)
 {
-	u32 i, pir_val;
+	u32 i, vec;
+	u32 pir_val, irr_val;
+	int max_irr = -1;

-	for (i = 0; i <= 7; i++) {
+	for (i = vec = 0; i <= 7; i++, vec += 32) {

how about ignore the first 32 vectors since they cannot be used as normal interrupt except nmi interrupt which is special handled.

 		pir_val = READ_ONCE(pir[i]);
+		irr_val = *((u32 *)(regs + APIC_IRR + i * 0x10));
 		if (pir_val) {
-			pir_val = xchg(&pir[i], 0);
-			*((u32 *)(regs + APIC_IRR + i * 0x10)) |= pir_val;
+			irr_val |= xchg(&pir[i], 0);
+			*((u32 *)(regs + APIC_IRR + i * 0x10)) = irr_val;
 		}
+		if (irr_val)
+			max_irr = __fls(irr_val) + vec;
 	}
+
+	return max_irr;
 }
 EXPORT_SYMBOL_GPL(__kvm_apic_update_irr);

-void kvm_apic_update_irr(struct kvm_vcpu *vcpu, u32 *pir)
+int kvm_apic_update_irr(struct kvm_vcpu *vcpu, u32 *pir)
 {
 	struct kvm_lapic *apic = vcpu->arch.apic;

-	__kvm_apic_update_irr(pir, apic->regs);
+	return __kvm_apic_update_irr(pir, apic->regs);
 }
 EXPORT_SYMBOL_GPL(kvm_apic_update_irr);

@@ -376,7 +383,7 @@ static inline int apic_find_highest_irr(struct kvm_lapic *apic)
 		return -1;

 	if (apic->vcpu->arch.apicv_active)
-		kvm_x86_ops->sync_pir_to_irr(apic->vcpu);
+		kvm_x86_ops->sync_pir_to_irr(apic->vcpu, false);
 	result = apic_search_irr(apic);

You have got the max_irr in sync_pir_to_irr. It seems the apic_search_irr() is redundant here.

 	ASSERT(result == -1 || result >= 16);

I think the result must >= 32. But it seems this code exists when kvm first merging into kernel.


diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h
index f60d01c29d51..fc72828c3782 100644
--- a/arch/x86/kvm/lapic.h
+++ b/arch/x86/kvm/lapic.h
@@ -70,8 +70,8 @@ int kvm_lapic_reg_read(struct kvm_lapic *apic, u32 offset, int len,
 bool kvm_apic_match_dest(struct kvm_vcpu *vcpu, struct kvm_lapic *source,
 			   int short_hand, unsigned int dest, int dest_mode);

-void __kvm_apic_update_irr(u32 *pir, void *regs);
-void kvm_apic_update_irr(struct kvm_vcpu *vcpu, u32 *pir);
+int __kvm_apic_update_irr(u32 *pir, void *regs);
+int kvm_apic_update_irr(struct kvm_vcpu *vcpu, u32 *pir);
 int kvm_apic_set_irq(struct kvm_vcpu *vcpu, struct kvm_lapic_irq *irq,
 		     struct dest_map *dest_map);
 int kvm_apic_local_deliver(struct kvm_lapic *apic, int lvt_type);
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 9b4221471e3d..60e53fa2b554 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -4383,7 +4383,7 @@ static void svm_load_eoi_exitmap(struct kvm_vcpu *vcpu, u64 *eoi_exit_bitmap)
 	return;
 }

-static void svm_sync_pir_to_irr(struct kvm_vcpu *vcpu)
+static void svm_sync_pir_to_irr(struct kvm_vcpu *vcpu, bool sync_rvi)
 {
 	return;
 }
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 207b9aa32915..1edefab54d01 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -4852,17 +4852,6 @@ static void vmx_deliver_posted_interrupt(struct kvm_vcpu *vcpu, int vector)
 		kvm_vcpu_kick(vcpu);
 }

-static void vmx_sync_pir_to_irr(struct kvm_vcpu *vcpu)
-{
-	struct vcpu_vmx *vmx = to_vmx(vcpu);
-
-	if (!pi_test_on(&vmx->pi_desc) ||
-	    !pi_test_and_clear_on(&vmx->pi_desc))
-		return;
-
-	kvm_apic_update_irr(vcpu, vmx->pi_desc.pir);
-}
-
 /*
  * Set up the vmcs's constant host-state fields, i.e., host-state fields that
  * will not change in the lifetime of the guest.
@@ -8609,6 +8598,20 @@ static void vmx_hwapic_irr_update(struct kvm_vcpu *vcpu, int max_irr)
 	}
 }

+static void vmx_sync_pir_to_irr(struct kvm_vcpu *vcpu, bool sync_rvi)
+{
+	struct vcpu_vmx *vmx = to_vmx(vcpu);
+	int max_irr;
+
+	if (!pi_test_on(&vmx->pi_desc) ||
+	    !pi_test_and_clear_on(&vmx->pi_desc))
+		return;
+
+	max_irr = kvm_apic_update_irr(vcpu, vmx->pi_desc.pir);
+	if (sync_rvi)
+		vmx_hwapic_irr_update(vcpu, max_irr);
+}
+
 static void vmx_load_eoi_exitmap(struct kvm_vcpu *vcpu, u64 *eoi_exit_bitmap)
 {
 	if (!kvm_vcpu_apicv_active(vcpu))
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 604cfbfc5bee..148e14fdc55d 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2821,7 +2821,7 @@ static int kvm_vcpu_ioctl_get_lapic(struct kvm_vcpu *vcpu,
 				    struct kvm_lapic_state *s)
 {
 	if (vcpu->arch.apicv_active)
-		kvm_x86_ops->sync_pir_to_irr(vcpu);
+		kvm_x86_ops->sync_pir_to_irr(vcpu, false);

 	return kvm_apic_get_state(vcpu, s);
 }
@@ -6448,7 +6448,7 @@ static void vcpu_scan_ioapic(struct kvm_vcpu *vcpu)
 		kvm_scan_ioapic_routes(vcpu, vcpu->arch.ioapic_handled_vectors);
 	else {
 		if (vcpu->arch.apicv_active)
-			kvm_x86_ops->sync_pir_to_irr(vcpu);
+			kvm_x86_ops->sync_pir_to_irr(vcpu, false);
 		kvm_ioapic_scan_entry(vcpu, vcpu->arch.ioapic_handled_vectors);
 	}
 	bitmap_or((ulong *)eoi_exit_bitmap, vcpu->arch.ioapic_handled_vectors,
@@ -6611,8 +6611,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 		 * virtual interrupt delivery.
 		 */
 		if (vcpu->arch.apicv_active)
-			kvm_x86_ops->hwapic_irr_update(vcpu,
-				kvm_lapic_find_highest_irr(vcpu));
+			kvm_x86_ops->sync_pir_to_irr(vcpu, true);
 	}

 	if (kvm_check_request(KVM_REQ_EVENT, vcpu) || req_int_win) {



--
Yang
Alibaba Cloud Computing
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