kvm: LAPIC: write down valid APIC registers

Replace a magic 64-bit mask with a list of valid registers, computing
the same mask in the end.
Suggested-by: Liran Alon <liran.alon@oracle.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/lapic.c

@@ -1312,25 +1312,45 @@ static inline struct kvm_lapic *to_lapic(struct kvm_io_device *dev)
 	return container_of(dev, struct kvm_lapic, dev);
 }
 
+#define APIC_REG_MASK(reg)	(1ull << ((reg) >> 4))
+#define APIC_REGS_MASK(first, count) \
+	(APIC_REG_MASK(first) * ((1ull << (count)) - 1))
+
 int kvm_lapic_reg_read(struct kvm_lapic *apic, u32 offset, int len,
 		void *data)
 {
 	unsigned char alignment = offset & 0xf;
 	u32 result;
 	/* this bitmask has a bit cleared for each reserved register */
-	u64 rmask = 0x43ff01ffffffe70cULL;
-
-	if ((alignment + len) > 4) {
-		apic_debug("KVM_APIC_READ: alignment error %x %d\n",
-			   offset, len);
-		return 1;
-	}
-
-	/* ARBPRI is also reserved on x2APIC */
-	if (apic_x2apic_mode(apic))
-		rmask &= ~(1 << (APIC_ARBPRI >> 4));
+	u64 valid_reg_mask =
+		APIC_REG_MASK(APIC_ID) |
+		APIC_REG_MASK(APIC_LVR) |
+		APIC_REG_MASK(APIC_TASKPRI) |
+		APIC_REG_MASK(APIC_PROCPRI) |
+		APIC_REG_MASK(APIC_LDR) |
+		APIC_REG_MASK(APIC_DFR) |
+		APIC_REG_MASK(APIC_SPIV) |
+		APIC_REGS_MASK(APIC_ISR, APIC_ISR_NR) |
+		APIC_REGS_MASK(APIC_TMR, APIC_ISR_NR) |
+		APIC_REGS_MASK(APIC_IRR, APIC_ISR_NR) |
+		APIC_REG_MASK(APIC_ESR) |
+		APIC_REG_MASK(APIC_ICR) |
+		APIC_REG_MASK(APIC_ICR2) |
+		APIC_REG_MASK(APIC_LVTT) |
+		APIC_REG_MASK(APIC_LVTTHMR) |
+		APIC_REG_MASK(APIC_LVTPC) |
+		APIC_REG_MASK(APIC_LVT0) |
+		APIC_REG_MASK(APIC_LVT1) |
+		APIC_REG_MASK(APIC_LVTERR) |
+		APIC_REG_MASK(APIC_TMICT) |
+		APIC_REG_MASK(APIC_TMCCT) |
+		APIC_REG_MASK(APIC_TDCR);
+
+	/* ARBPRI is not valid on x2APIC */
+	if (!apic_x2apic_mode(apic))
+		valid_reg_mask |= APIC_REG_MASK(APIC_ARBPRI);
 
-	if (offset > 0x3f0 || !(rmask & (1ULL << (offset >> 4)))) {
+	if (offset > 0x3f0 || !(valid_reg_mask & APIC_REG_MASK(offset))) {
 		apic_debug("KVM_APIC_READ: read reserved register %x\n",
 			   offset);
 		return 1;