linux-kernel - [PATCH] KVM: split kvm_vcpu_wake_up from kvm_vcpu

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Date:	Thu, 17 Mar 2016 21:27:27 +0100
From:	Radim Krčmář <rkrcmar@...hat.com>
To:	Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>
Cc:	pbonzini@...hat.com, joro@...tes.org, bp@...en8.de,
	gleb@...nel.org, alex.williamson@...hat.com, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, wei@...hat.com,
	sherry.hurwitz@....com
Subject: [PATCH] KVM: split kvm_vcpu_wake_up from kvm_vcpu_kick

2016-03-18 02:44+0700, Suravee Suthikulpanit:
> On 3/10/16 03:55, Radim Krčmář wrote:
>>2016-03-04 14:46-0600, Suravee Suthikulpanit:
>>>>From: Suravee Suthikulpanit<suravee.suthikulpanit@....com>
>>>>
>>>>Introduce VMEXIT handlers, avic_incp_ipi_interception() and
>>>>avic_noaccel_interception().
>>>>
>>>>Signed-off-by: Suravee Suthikulpanit<suravee.suthikulpanit@....com>
>>>>---
>>>>diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
>>>>@@ -3690,6 +3690,264 @@ static int mwait_interception(struct vcpu_svm *svm)
>>>>+	case AVIC_INCMP_IPI_ERR_TARGET_NOT_RUN: {
>>>>+		kvm_for_each_vcpu(i, vcpu, kvm) {
>>>>+			if (!kvm_apic_match_dest(vcpu, apic,
>>>>+						 icrl & APIC_SHORT_MASK,
>>>>+						 GET_APIC_DEST_FIELD(icrh),
>>>>+						 icrl & APIC_DEST_MASK))
>>>>+				continue;
>>>>+
>>>>+			kvm_vcpu_kick(vcpu);
>>KVM shouldn't kick VCPUs that are running.  (Imagine a broadcast when
>>most VCPUs are in guest mode.)
> 
> So, besides checking if the vcpu match the destination, I will add the check
> to see if the is_running bit is set before calling kvm_vcpu_kick()

That will do.

>>I think a new helper might be useful here: we only want to wake up from
>>wait queue, but never force VCPU out of guest mode ... kvm_vcpu_kick()
>>does both.
> 
> If I only kick non-running vcpu, do I still need this new helper function?

I would prefer it.  It's a minor performance optimization (non-running
VCPUs aren't in guest mode) and makes our intent clear.  Please use
include the following patch and use kvm_vcpu_wake_up instead.

---8<---
AVIC has a use for kvm_vcpu_wake_up.

Signed-off-by: Radim Krčmář <rkrcmar@...hat.com>
---
 include/linux/kvm_host.h |  1 +
 virt/kvm/kvm_main.c      | 19 +++++++++++++------
 2 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 861f690aa791..7b269626a3b3 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -650,6 +650,7 @@ void kvm_vcpu_mark_page_dirty(struct kvm_vcpu *vcpu, gfn_t gfn);
 void kvm_vcpu_block(struct kvm_vcpu *vcpu);
 void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu);
 void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu);
+void kvm_vcpu_wake_up(struct kvm_vcpu *vcpu);
 void kvm_vcpu_kick(struct kvm_vcpu *vcpu);
 int kvm_vcpu_yield_to(struct kvm_vcpu *target);
 void kvm_vcpu_on_spin(struct kvm_vcpu *vcpu);
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 1eae05236347..c39c54afdb74 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2054,13 +2054,8 @@ out:
 EXPORT_SYMBOL_GPL(kvm_vcpu_block);
 
 #ifndef CONFIG_S390
-/*
- * Kick a sleeping VCPU, or a guest VCPU in guest mode, into host kernel mode.
- */
-void kvm_vcpu_kick(struct kvm_vcpu *vcpu)
+void kvm_vcpu_wake_up(struct kvm_vcpu *vcpu)
 {
-	int me;
-	int cpu = vcpu->cpu;
 	wait_queue_head_t *wqp;
 
 	wqp = kvm_arch_vcpu_wq(vcpu);
@@ -2068,6 +2063,18 @@ void kvm_vcpu_kick(struct kvm_vcpu *vcpu)
 		wake_up_interruptible(wqp);
 		++vcpu->stat.halt_wakeup;
 	}
+}
+EXPORT_SYMBOL_GPL(kvm_vcpu_wake_up);
+
+/*
+ * Kick a sleeping VCPU, or a guest VCPU in guest mode, into host kernel mode.
+ */
+void kvm_vcpu_kick(struct kvm_vcpu *vcpu)
+{
+	int me;
+	int cpu = vcpu->cpu;
+
+	kvm_vcpu_wake_up(vcpu);
 
 	me = get_cpu();
 	if (cpu != me && (unsigned)cpu < nr_cpu_ids && cpu_online(cpu))
-- 
2.7.2