KVM: x86: #GP when attempts to write reserved bits of Variable Range MTRRs

Section 11.11.2.3 of the SDM mentions "All other bits in the IA32_MTRR_PHYSBASEn
and IA32_MTRR_PHYSMASKn registers are reserved; the processor generates a
general-protection exception(#GP) if software attempts to write to them". This
patch do it in kvm.
Signed-off-by: Wanpeng Li <wanpeng.li@linux.intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/x86.c

@@ -1726,6 +1726,7 @@ static bool valid_mtrr_type(unsigned t)
 static bool mtrr_valid(struct kvm_vcpu *vcpu, u32 msr, u64 data)
 {
 	int i;
+	u64 mask = 0;
 
 	if (!msr_mtrr_valid(msr))
 		return false;
@@ -1749,10 +1750,21 @@ static bool mtrr_valid(struct kvm_vcpu *vcpu, u32 msr, u64 data)
 	/* variable MTRRs */
 	WARN_ON(!(msr >= 0x200 && msr < 0x200 + 2 * KVM_NR_VAR_MTRR));
 
-	if ((msr & 1) == 0)
+	for (i = 63; i > boot_cpu_data.x86_phys_bits; i--)
+		mask |= (1ULL << i);
+	if ((msr & 1) == 0) {
 		/* MTRR base */
-		return valid_mtrr_type(data & 0xff);
+		if (!valid_mtrr_type(data & 0xff))
+			return false;
+		mask |= 0xf00;
+	} else
 		/* MTRR mask */
+		mask |= 0x7ff;
+	if (data & mask) {
+		kvm_inject_gp(vcpu, 0);
+		return false;
+	}
+
 	return true;
 }