KVM: make make_all_cpus_request() lockless

Now, we have 'vcpu->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@cn.fujitsu.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index b99eacd..c8dee22 100644 (file)
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -224,7 +224,6 @@ 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;
@@ -731,11 +730,6 @@ 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 19209f8..4856a7d 100644 (file)
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -165,11 +165,9 @@ 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;
+               kvm_make_request(req, vcpu);
                cpu = vcpu->cpu;
 
                /* Set ->requests bit before we read ->mode */
@@ -185,7 +183,7 @@ 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;
 }
@@ -468,7 +466,6 @@ 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);