KVM: x86: emulator injects #DB when RFLAGS.RF is set

If the RFLAGS.RF is set, then no #DB should occur on instruction breakpoints.
However, the KVM emulator injects #DB regardless to RFLAGS.RF. This patch fixes
this behavior. KVM, however, still appears not to update RFLAGS.RF correctly,
regardless of this patch.
Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/x86.c

@@ -5158,7 +5158,8 @@ static bool kvm_vcpu_check_breakpoint(struct kvm_vcpu *vcpu, int *r)
 		}
 	}
 
-	if (unlikely(vcpu->arch.dr7 & DR7_BP_EN_MASK)) {
+	if (unlikely(vcpu->arch.dr7 & DR7_BP_EN_MASK) &&
+	    !(kvm_get_rflags(vcpu) & X86_EFLAGS_RF)) {
 		dr6 = kvm_vcpu_check_hw_bp(eip, 0,
 					   vcpu->arch.dr7,
 					   vcpu->arch.db);