MIPS: KVM: Fix 64-bit big endian dynamic translation

The MFC0 and MTC0 instructions in the guest which cause traps can be
replaced with 32-bit loads and stores to the commpage, however on big
endian 64-bit builds the offset needs to have 4 added so as to
load/store the least significant half of the long instead of the most
significant half.
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: linux-mips@linux-mips.org
Cc: kvm@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/mips/kvm/dyntrans.c

@@ -103,6 +103,10 @@ int kvm_mips_trans_mfc0(union mips_instruction inst, u32 *opc,
 		mfc0_inst.i_format.rt = inst.c0r_format.rt;
 		mfc0_inst.i_format.simmediate = KVM_GUEST_COMMPAGE_ADDR |
 			offsetof(struct kvm_mips_commpage, cop0.reg[rd][sel]);
+#ifdef CONFIG_CPU_BIG_ENDIAN
+		if (sizeof(vcpu->arch.cop0->reg[0][0]) == 8)
+			mfc0_inst.i_format.simmediate |= 4;
+#endif
 	}
 
 	return kvm_mips_trans_replace(vcpu, opc, mfc0_inst);
@@ -121,6 +125,10 @@ int kvm_mips_trans_mtc0(union mips_instruction inst, u32 *opc,
 	mtc0_inst.i_format.rt = inst.c0r_format.rt;
 	mtc0_inst.i_format.simmediate = KVM_GUEST_COMMPAGE_ADDR |
 		offsetof(struct kvm_mips_commpage, cop0.reg[rd][sel]);
+#ifdef CONFIG_CPU_BIG_ENDIAN
+	if (sizeof(vcpu->arch.cop0->reg[0][0]) == 8)
+		mtc0_inst.i_format.simmediate |= 4;
+#endif
 
 	return kvm_mips_trans_replace(vcpu, opc, mtc0_inst);
 }