KVM: x86: change vcpu->arch.switch_db_regs to a bit mask

The next patch will add another bit that we can test with the
same "if".
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

arch/x86/include/asm/kvm_host.h

@@ -337,6 +337,10 @@ struct kvm_pmu {
 	u64 reprogram_pmi;
 };
 
+enum {
+	KVM_DEBUGREG_BP_ENABLED = 1,
+};
+
 struct kvm_vcpu_arch {
 	/*
 	 * rip and regs accesses must go through
@@ -463,7 +467,7 @@ struct kvm_vcpu_arch {
 	struct mtrr_state_type mtrr_state;
 	u32 pat;
 
-	int switch_db_regs;
+	unsigned switch_db_regs;
 	unsigned long db[KVM_NR_DB_REGS];
 	unsigned long dr6;
 	unsigned long dr7;

arch/x86/kvm/x86.c

@@ -759,7 +759,9 @@ static void kvm_update_dr7(struct kvm_vcpu *vcpu)
 	else
 		dr7 = vcpu->arch.dr7;
 	kvm_x86_ops->set_dr7(vcpu, dr7);
-	vcpu->arch.switch_db_regs = (dr7 & DR7_BP_EN_MASK);
+	vcpu->arch.switch_db_regs &= ~KVM_DEBUGREG_BP_ENABLED;
+	if (dr7 & DR7_BP_EN_MASK)
+		vcpu->arch.switch_db_regs |= KVM_DEBUGREG_BP_ENABLED;
 }
 
 static int __kvm_set_dr(struct kvm_vcpu *vcpu, int dr, unsigned long val)