MIPS: KVM: Sign extend MFC0/RDHWR results

When emulating MFC0 instructions to load 32-bit values from guest COP0
registers and the RDHWR instruction to read the CC (Count) register,
sign extend the result to comply with the MIPS64 architecture. The
result must be in canonical 32-bit form or the guest may malfunction.

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>

diff --git a/arch/mips/kvm/emulate.c b/arch/mips/kvm/emulate.c
index be18dfe9ecaa210b23f6e7c1dd1f1368efd675dc..6eb52b9c98183b95134710c22187b1a6f0225ef9 100644 (file)
--- a/arch/mips/kvm/emulate.c
+++ b/arch/mips/kvm/emulate.c
@@ -1072,14 +1072,15 @@ enum emulation_result kvm_mips_emulate_CP0(union mips_instruction inst,
 #endif
                        /* Get reg */
                        if ((rd == MIPS_CP0_COUNT) && (sel == 0)) {
-                               vcpu->arch.gprs[rt] = kvm_mips_read_count(vcpu);
+                               vcpu->arch.gprs[rt] =
+                                   (s32)kvm_mips_read_count(vcpu);
                        } else if ((rd == MIPS_CP0_ERRCTL) && (sel == 0)) {
                                vcpu->arch.gprs[rt] = 0x0;
 #ifdef CONFIG_KVM_MIPS_DYN_TRANS
                                kvm_mips_trans_mfc0(inst, opc, vcpu);
 #endif
                        } else {
-                               vcpu->arch.gprs[rt] = cop0->reg[rd][sel];
+                               vcpu->arch.gprs[rt] = (s32)cop0->reg[rd][sel];
 
 #ifdef CONFIG_KVM_MIPS_DYN_TRANS
                                kvm_mips_trans_mfc0(inst, opc, vcpu);
@@ -2380,7 +2381,7 @@ enum emulation_result kvm_mips_handle_ri(u32 cause, u32 *opc,
                                             current_cpu_data.icache.linesz);
                        break;
                case MIPS_HWR_CC:               /* Read count register */
-                       arch->gprs[rt] = kvm_mips_read_count(vcpu);
+                       arch->gprs[rt] = (s32)kvm_mips_read_count(vcpu);
                        break;
                case MIPS_HWR_CCRES:            /* Count register resolution */
                        switch (current_cpu_data.cputype) {