linux-kernel - [PATCH v3 13/26] KVM: SVM: Use kvm_vcpu_is_blocking() in AVIC load to handle preemption

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Message-Id: <20211208015236.1616697-14-seanjc@google.com>
Date:   Wed,  8 Dec 2021 01:52:23 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>, Joerg Roedel <joro@...tes.org>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
        kvm@...r.kernel.org, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, Maxim Levitsky <mlevitsk@...hat.com>
Subject: [PATCH v3 13/26] KVM: SVM: Use kvm_vcpu_is_blocking() in AVIC load to
 handle preemption

Use kvm_vcpu_is_blocking() to determine whether or not the vCPU should be
marked running during avic_vcpu_load().  Drop avic_is_running, which
really should have been named "vcpu_is_not_blocking", as it tracked if
the vCPU was blocking, not if it was actually running, e.g. it was set
during svm_create_vcpu() when the vCPU was obviously not running.

This is technically a teeny tiny functional change, as the vCPU will be
marked IsRunning=1 on being reloaded if the vCPU is preempted between
svm_vcpu_blocking() and prepare_to_rcuwait().  But that's a benign change
as the vCPU will be marked IsRunning=0 when KVM voluntarily schedules out
the vCPU.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/svm/avic.c | 14 +++++++++-----
 arch/x86/kvm/svm/svm.c  |  6 ------
 arch/x86/kvm/svm/svm.h  |  1 -
 3 files changed, 9 insertions(+), 12 deletions(-)

diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
index 16e4ebd980a2..dc0cbe500106 100644
--- a/arch/x86/kvm/svm/avic.c
+++ b/arch/x86/kvm/svm/avic.c
@@ -974,6 +974,7 @@ void avic_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 {
 	u64 entry;
 	/* ID = 0xff (broadcast), ID > 0xff (reserved) */
+	bool is_blocking = kvm_vcpu_is_blocking(vcpu);
 	int h_physical_id = kvm_cpu_get_apicid(cpu);
 	struct vcpu_svm *svm = to_svm(vcpu);
 
@@ -991,12 +992,17 @@ void avic_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 	entry |= (h_physical_id & AVIC_PHYSICAL_ID_ENTRY_HOST_PHYSICAL_ID_MASK);
 
 	entry &= ~AVIC_PHYSICAL_ID_ENTRY_IS_RUNNING_MASK;
-	if (svm->avic_is_running)
+
+	/*
+	 * Don't mark the vCPU as running if its blocking, i.e. if the vCPU is
+	 * preempted after svm_vcpu_blocking() but before KVM voluntarily
+	 * schedules out the vCPU.
+	 */
+	if (!is_blocking)
 		entry |= AVIC_PHYSICAL_ID_ENTRY_IS_RUNNING_MASK;
 
 	WRITE_ONCE(*(svm->avic_physical_id_cache), entry);
-	avic_update_iommu_vcpu_affinity(vcpu, h_physical_id,
-					svm->avic_is_running);
+	avic_update_iommu_vcpu_affinity(vcpu, h_physical_id, !is_blocking);
 }
 
 void avic_vcpu_put(struct kvm_vcpu *vcpu)
@@ -1017,11 +1023,9 @@ void avic_vcpu_put(struct kvm_vcpu *vcpu)
  */
 static void avic_set_running(struct kvm_vcpu *vcpu, bool is_run)
 {
-	struct vcpu_svm *svm = to_svm(vcpu);
 	int cpu = get_cpu();
 
 	WARN_ON(cpu != vcpu->cpu);
-	svm->avic_is_running = is_run;
 
 	if (kvm_vcpu_apicv_active(vcpu)) {
 		if (is_run)
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 208566f63bce..dde0106ffc47 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -1444,12 +1444,6 @@ static int svm_create_vcpu(struct kvm_vcpu *vcpu)
 	if (err)
 		goto error_free_vmsa_page;
 
-	/* We initialize this flag to true to make sure that the is_running
-	 * bit would be set the first time the vcpu is loaded.
-	 */
-	if (irqchip_in_kernel(vcpu->kvm) && kvm_apicv_activated(vcpu->kvm))
-		svm->avic_is_running = true;
-
 	svm->msrpm = svm_vcpu_alloc_msrpm();
 	if (!svm->msrpm) {
 		err = -ENOMEM;
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index ca51d6dfc8e6..83ced47fa9b9 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -226,7 +226,6 @@ struct vcpu_svm {
 	u32 dfr_reg;
 	struct page *avic_backing_page;
 	u64 *avic_physical_id_cache;
-	bool avic_is_running;
 
 	/*
 	 * Per-vcpu list of struct amd_svm_iommu_ir:
-- 
2.34.1.400.ga245620fadb-goog