KVM: add kvm_request_pending

A first step in vcpu->requests encapsulation.  Additionally, we now
use READ_ONCE() when accessing vcpu->requests, which ensures we
always load vcpu->requests when it's accessed.  This is important as
other threads can change it any time.  Also, READ_ONCE() documents
that vcpu->requests is used with other threads, likely requiring
memory barriers, which it does.

Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
[ Documented the new use of READ_ONCE() and converted another check
  in arch/mips/kvm/vz.c ]
Signed-off-by: Andrew Jones <drjones@redhat.com>
Acked-by: Christoffer Dall <cdall@linaro.org>
Signed-off-by: Christoffer Dall <cdall@linaro.org>
diff --git a/arch/mips/kvm/vz.c b/arch/mips/kvm/vz.c
index 71d8856..7480503 100644
--- a/arch/mips/kvm/vz.c
+++ b/arch/mips/kvm/vz.c
@@ -2337,7 +2337,7 @@ static int kvm_vz_check_requests(struct kvm_vcpu *vcpu, int cpu)
 	int ret = 0;
 	int i;
 
-	if (!vcpu->requests)
+	if (!kvm_request_pending(vcpu))
 		return 0;
 
 	if (kvm_check_request(KVM_REQ_TLB_FLUSH, vcpu)) {