KVM: x86: Add helpers to handle 64-bit APIC MSR read/writes

Add helpers to handle 64-bit APIC read/writes via MSRs to deduplicate the
x2APIC and Hyper-V code needed to service reads/writes to ICR.  Future
support for IPI virtualization will add yet another path where KVM must
handle 64-bit APIC MSR reads/write (to ICR).

Opportunistically fix the comment in the write path; ICR2 holds the
destination (if there's no shorthand), not the vector.

No functional change intended.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20220204214205.3306634-9-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/lapic.c

@@ -2774,6 +2774,30 @@ int kvm_lapic_set_vapic_addr(struct kvm_vcpu *vcpu, gpa_t vapic_addr)
 	return 0;
 }
 
+static int kvm_lapic_msr_read(struct kvm_lapic *apic, u32 reg, u64 *data)
+{
+	u32 low, high = 0;
+
+	if (kvm_lapic_reg_read(apic, reg, 4, &low))
+		return 1;
+
+	if (reg == APIC_ICR &&
+	    WARN_ON_ONCE(kvm_lapic_reg_read(apic, APIC_ICR2, 4, &high)))
+		return 1;
+
+	*data = (((u64)high) << 32) | low;
+
+	return 0;
+}
+
+static int kvm_lapic_msr_write(struct kvm_lapic *apic, u32 reg, u64 data)
+{
+	/* For 64-bit ICR writes, set ICR2 (dest) before ICR (command). */
+	if (reg == APIC_ICR)
+		kvm_lapic_reg_write(apic, APIC_ICR2, (u32)(data >> 32));
+	return kvm_lapic_reg_write(apic, reg, (u32)data);
+}
+
 int kvm_x2apic_msr_write(struct kvm_vcpu *vcpu, u32 msr, u64 data)
 {
 	struct kvm_lapic *apic = vcpu->arch.apic;
@@ -2785,16 +2809,13 @@ int kvm_x2apic_msr_write(struct kvm_vcpu *vcpu, u32 msr, u64 data)
 	if (reg == APIC_ICR2)
 		return 1;
 
-	/* if this is ICR write vector before command */
-	if (reg == APIC_ICR)
-		kvm_lapic_reg_write(apic, APIC_ICR2, (u32)(data >> 32));
-	return kvm_lapic_reg_write(apic, reg, (u32)data);
+	return kvm_lapic_msr_write(apic, reg, data);
 }
 
 int kvm_x2apic_msr_read(struct kvm_vcpu *vcpu, u32 msr, u64 *data)
 {
 	struct kvm_lapic *apic = vcpu->arch.apic;
-	u32 reg = (msr - APIC_BASE_MSR) << 4, low, high = 0;
+	u32 reg = (msr - APIC_BASE_MSR) << 4;
 
 	if (!lapic_in_kernel(vcpu) || !apic_x2apic_mode(apic))
 		return 1;
@@ -2802,45 +2823,23 @@ int kvm_x2apic_msr_read(struct kvm_vcpu *vcpu, u32 msr, u64 *data)
 	if (reg == APIC_DFR || reg == APIC_ICR2)
 		return 1;
 
-	if (kvm_lapic_reg_read(apic, reg, 4, &low))
-		return 1;
-	if (reg == APIC_ICR)
-		kvm_lapic_reg_read(apic, APIC_ICR2, 4, &high);
-
-	*data = (((u64)high) << 32) | low;
-
-	return 0;
+	return kvm_lapic_msr_read(apic, reg, data);
 }
 
 int kvm_hv_vapic_msr_write(struct kvm_vcpu *vcpu, u32 reg, u64 data)
 {
-	struct kvm_lapic *apic = vcpu->arch.apic;
-
 	if (!lapic_in_kernel(vcpu))
 		return 1;
 
-	/* if this is ICR write vector before command */
-	if (reg == APIC_ICR)
-		kvm_lapic_reg_write(apic, APIC_ICR2, (u32)(data >> 32));
-	return kvm_lapic_reg_write(apic, reg, (u32)data);
+	return kvm_lapic_msr_write(vcpu->arch.apic, reg, data);
 }
 
 int kvm_hv_vapic_msr_read(struct kvm_vcpu *vcpu, u32 reg, u64 *data)
 {
-	struct kvm_lapic *apic = vcpu->arch.apic;
-	u32 low, high = 0;
-
 	if (!lapic_in_kernel(vcpu))
 		return 1;
 
-	if (kvm_lapic_reg_read(apic, reg, 4, &low))
-		return 1;
-	if (reg == APIC_ICR)
-		kvm_lapic_reg_read(apic, APIC_ICR2, 4, &high);
-
-	*data = (((u64)high) << 32) | low;
-
-	return 0;
+	return kvm_lapic_msr_read(vcpu->arch.apic, reg, data);
 }
 
 int kvm_lapic_set_pv_eoi(struct kvm_vcpu *vcpu, u64 data, unsigned long len)