linux-kernel - [PATCH 2/2] KVM: X86: Implement PV send IPI support

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Date:   Fri, 29 Jun 2018 17:51:16 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>
Subject: [PATCH 2/2] KVM: X86: Implement PV send IPI support

From: Wanpeng Li <wanpengli@...cent.com>

Using hypercall to send IPIs by one vmexit instead of one by one for
xAPIC/x2APIC physical mode and one vmexit per-cluster for x2APIC cluster 
mode. 

Even if enable qemu interrupt remapping and PV TLB Shootdown, I can still 
observe ~14% performance boost by ebizzy benchmark for 64 vCPUs VM, the 
total msr-induced vmexits reduce ~70%.

Cc: Paolo Bonzini <pbonzini@...hat.com>
Cc: Radim Krčmář <rkrcmar@...hat.com>
Cc: Vitaly Kuznetsov <vkuznets@...hat.com>
Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
---
 Documentation/virtual/kvm/cpuid.txt |  4 ++++
 arch/x86/kvm/cpuid.c                |  3 ++-
 arch/x86/kvm/x86.c                  | 25 +++++++++++++++++++++++++
 include/uapi/linux/kvm_para.h       |  1 +
 4 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/Documentation/virtual/kvm/cpuid.txt b/Documentation/virtual/kvm/cpuid.txt
index ab022dc..d72359f 100644
--- a/Documentation/virtual/kvm/cpuid.txt
+++ b/Documentation/virtual/kvm/cpuid.txt
@@ -62,6 +62,10 @@ KVM_FEATURE_ASYNC_PF_VMEXIT        ||    10 || paravirtualized async PF VM exit
                                    ||       || can be enabled by setting bit 2
                                    ||       || when writing to msr 0x4b564d02
 ------------------------------------------------------------------------------
+KVM_FEATURE_PV_SEND_IPI            ||    11 || guest checks this feature bit
+                                   ||       || before enabling paravirtualized
+                                   ||       || send IPIs.
+------------------------------------------------------------------------------
 KVM_FEATURE_CLOCKSOURCE_STABLE_BIT ||    24 || host will warn if no guest-side
                                    ||       || per-cpu warps are expected in
                                    ||       || kvmclock.
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 7e042e3..7bcfa61 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -621,7 +621,8 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
 			     (1 << KVM_FEATURE_CLOCKSOURCE_STABLE_BIT) |
 			     (1 << KVM_FEATURE_PV_UNHALT) |
 			     (1 << KVM_FEATURE_PV_TLB_FLUSH) |
-			     (1 << KVM_FEATURE_ASYNC_PF_VMEXIT);
+			     (1 << KVM_FEATURE_ASYNC_PF_VMEXIT) |
+			     (1 << KVM_FEATURE_PV_SEND_IPI);
 
 		if (sched_info_on())
 			entry->eax |= (1 << KVM_FEATURE_STEAL_TIME);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 0046aa7..c2e6cdb 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6689,6 +6689,27 @@ static void kvm_pv_kick_cpu_op(struct kvm *kvm, unsigned long flags, int apicid)
 	kvm_irq_delivery_to_apic(kvm, NULL, &lapic_irq, NULL);
 }
 
+static void kvm_pv_send_ipi(struct kvm *kvm, unsigned long ipi_bitmap, u8 vector)
+{
+	struct kvm_apic_map *map;
+	struct kvm_vcpu *vcpu;
+	struct kvm_lapic_irq lapic_irq = {0};
+	int i;
+
+	lapic_irq.delivery_mode = APIC_DM_FIXED;
+	lapic_irq.vector = vector;
+
+	rcu_read_lock();
+	map = rcu_dereference(kvm->arch.apic_map);
+
+	for_each_set_bit(i, &ipi_bitmap, sizeof(unsigned long)) {
+		vcpu = map->phys_map[i]->vcpu;
+		kvm_apic_set_irq(vcpu, &lapic_irq, NULL);
+	}
+
+	rcu_read_unlock();
+}
+
 void kvm_vcpu_deactivate_apicv(struct kvm_vcpu *vcpu)
 {
 	vcpu->arch.apicv_active = false;
@@ -6738,6 +6759,10 @@ int kvm_emulate_hypercall(struct kvm_vcpu *vcpu)
 		ret = kvm_pv_clock_pairing(vcpu, a0, a1);
 		break;
 #endif
+	case KVM_HC_SEND_IPI:
+		kvm_pv_send_ipi(vcpu->kvm, a0, a1);
+		ret = 0;
+		break;
 	default:
 		ret = -KVM_ENOSYS;
 		break;
diff --git a/include/uapi/linux/kvm_para.h b/include/uapi/linux/kvm_para.h
index dcf629d..7395f38 100644
--- a/include/uapi/linux/kvm_para.h
+++ b/include/uapi/linux/kvm_para.h
@@ -26,6 +26,7 @@
 #define KVM_HC_MIPS_EXIT_VM		7
 #define KVM_HC_MIPS_CONSOLE_OUTPUT	8
 #define KVM_HC_CLOCK_PAIRING		9
+#define KVM_HC_SEND_IPI         	10
 
 /*
  * hypercalls use architecture specific
-- 
2.7.4