KVM: MIPS/VZ: Handle Octeon III guest.PRid register

Octeon III implements a read-only guest CP0_PRid register, so add cases
to the KVM register access API for Octeon to ensure the correct value is
read and writes are ignored.
Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Radim Krčmář" <rkrcmar@redhat.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: David Daney <david.daney@cavium.com>
Cc: Andreas Herrmann <andreas.herrmann@caviumnetworks.com>
Cc: linux-mips@linux-mips.org
Cc: kvm@vger.kernel.org

arch/mips/include/asm/mipsregs.h

@@ -2025,6 +2025,8 @@ do {									\
 #define read_gc0_epc()			__read_ulong_gc0_register(14, 0)
 #define write_gc0_epc(val)		__write_ulong_gc0_register(14, 0, val)
 
+#define read_gc0_prid()			__read_32bit_gc0_register(15, 0)
+
 #define read_gc0_ebase()		__read_32bit_gc0_register(15, 1)
 #define write_gc0_ebase(val)		__write_32bit_gc0_register(15, 1, val)
 

arch/mips/kvm/vz.c

@@ -1938,7 +1938,15 @@ static int kvm_vz_get_one_reg(struct kvm_vcpu *vcpu,
 		*v = (long)read_gc0_epc();
 		break;
 	case KVM_REG_MIPS_CP0_PRID:
-		*v = (long)kvm_read_c0_guest_prid(cop0);
+		switch (boot_cpu_type()) {
+		case CPU_CAVIUM_OCTEON3:
+			/* Octeon III has a read-only guest.PRid */
+			*v = read_gc0_prid();
+			break;
+		default:
+			*v = (long)kvm_read_c0_guest_prid(cop0);
+			break;
+		};
 		break;
 	case KVM_REG_MIPS_CP0_EBASE:
 		*v = kvm_vz_read_gc0_ebase();
@@ -2170,7 +2178,14 @@ static int kvm_vz_set_one_reg(struct kvm_vcpu *vcpu,
 		write_gc0_epc(v);
 		break;
 	case KVM_REG_MIPS_CP0_PRID:
-		kvm_write_c0_guest_prid(cop0, v);
+		switch (boot_cpu_type()) {
+		case CPU_CAVIUM_OCTEON3:
+			/* Octeon III has a guest.PRid, but its read-only */
+			break;
+		default:
+			kvm_write_c0_guest_prid(cop0, v);
+			break;
+		};
 		break;
 	case KVM_REG_MIPS_CP0_EBASE:
 		kvm_vz_write_gc0_ebase(v);