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>

2 files changed, 3 insertions, 12 deletions

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index b99eacd988ab..c8dee22b1945 100644
--- 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 19209f849cf7..4856a7dcbd7f 100644
--- 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);