[PATCH v2 3/3] KVM: make make_all_cpus_request() lockless

[Xiao Guangrong]

Now, we have 'vcpu->guest_mode' to judge whether need to send
ipi to other cpus, this way is very exact, so checking request
bit is needless, then we can drop the spinlock let it's collateral

Signed-off-by: Xiao Guangrong <xiaoguangrong@xxxxxxxxxxxxxx>
---
 include/linux/kvm_host.h |    6 ------
 virt/kvm/kvm_main.c      |   11 ++++-------
 2 files changed, 4 insertions(+), 13 deletions(-)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 5f5ef74..72b6dde 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -213,7 +213,6 @@ struct kvm_memslots {
 
 struct kvm {
 	spinlock_t mmu_lock;
-	raw_spinlock_t requests_lock;
 	struct mutex slots_lock;
 	struct mm_struct *mm; /* userspace tied to this vm */
 	struct kvm_memslots *memslots;
@@ -720,11 +719,6 @@ static inline void kvm_make_request(int req, struct kvm_vcpu *vcpu)
 	set_bit(req, &vcpu->requests);
 }
 
-static inline bool kvm_make_check_request(int req, struct kvm_vcpu *vcpu)
-{
-	return test_and_set_bit(req, &vcpu->requests);
-}
-
 static inline bool kvm_check_request(int req, struct kvm_vcpu *vcpu)
 {
 	if (test_bit(req, &vcpu->requests)) {
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index a475264..1afcdcd 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -147,16 +147,14 @@ static bool make_all_cpus_request(struct kvm *kvm, unsigned int req)
 
 	zalloc_cpumask_var(&cpus, GFP_ATOMIC);
 
-	raw_spin_lock(&kvm->requests_lock);
-	me = smp_processor_id();
+	me = get_cpu();
 	kvm_for_each_vcpu(i, vcpu, kvm) {
-		if (kvm_make_check_request(req, vcpu))
-			continue;
-		cpu = vcpu->cpu;
+		kvm_make_request(req, vcpu);
 
 		/* Set ->requests bit before we read ->guest_mode */
 		smp_mb();
 
+		cpu = vcpu->cpu;
 		if (cpus != NULL && cpu != -1 && cpu != me &&
 		      atomic_read(&vcpu->guest_mode))
 			cpumask_set_cpu(cpu, cpus);
@@ -167,7 +165,7 @@ static bool make_all_cpus_request(struct kvm *kvm, unsigned int req)
 		smp_call_function_many(cpus, ack_flush, NULL, 1);
 	else
 		called = false;
-	raw_spin_unlock(&kvm->requests_lock);
+	put_cpu();
 	free_cpumask_var(cpus);
 	return called;
 }
@@ -433,7 +431,6 @@ static struct kvm *kvm_create_vm(void)
 	kvm->mm = current->mm;
 	atomic_inc(&kvm->mm->mm_count);
 	spin_lock_init(&kvm->mmu_lock);
-	raw_spin_lock_init(&kvm->requests_lock);
 	kvm_eventfd_init(kvm);
 	mutex_init(&kvm->lock);
 	mutex_init(&kvm->irq_lock);
-- 
1.7.3.4

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