MIPS: KVM: Don't save/restore lo/hi for r6

MIPSr6 doesn't have lo/hi registers, so don't bother saving or
restoring them, and don't expose them to userland with the KVM ioctl
interface either.

In fact the lo/hi registers aren't callee saved in the MIPS ABIs anyway,
so there is no need to preserve the host lo/hi values at all when
transitioning to and from the guest (which happens via a function call).

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim KrÄmář <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/entry.c

@@ -178,12 +178,6 @@ void *kvm_mips_build_vcpu_run(void *addr)
 		UASM_i_SW(&p, i, offsetof(struct pt_regs, regs[i]), K1);
 	}
 
-	/* Save hi/lo */
-	uasm_i_mflo(&p, V0);
-	UASM_i_SW(&p, V0, offsetof(struct pt_regs, lo), K1);
-	uasm_i_mfhi(&p, V1);
-	UASM_i_SW(&p, V1, offsetof(struct pt_regs, hi), K1);
-
 	/* Save host status */
 	uasm_i_mfc0(&p, V0, C0_STATUS);
 	UASM_i_SW(&p, V0, offsetof(struct pt_regs, cp0_status), K1);
@@ -307,12 +301,14 @@ static void *kvm_mips_build_enter_guest(void *addr)
 		UASM_i_LW(&p, i, offsetof(struct kvm_vcpu_arch, gprs[i]), K1);
 	}
 
+#ifndef CONFIG_CPU_MIPSR6
 	/* Restore hi/lo */
 	UASM_i_LW(&p, K0, offsetof(struct kvm_vcpu_arch, hi), K1);
 	uasm_i_mthi(&p, K0);
 
 	UASM_i_LW(&p, K0, offsetof(struct kvm_vcpu_arch, lo), K1);
 	uasm_i_mtlo(&p, K0);
+#endif
 
 	/* Restore the guest's k0/k1 registers */
 	UASM_i_LW(&p, K0, offsetof(struct kvm_vcpu_arch, gprs[K0]), K1);
@@ -408,12 +404,14 @@ void *kvm_mips_build_exit(void *addr)
 		UASM_i_SW(&p, i, offsetof(struct kvm_vcpu_arch, gprs[i]), K1);
 	}
 
+#ifndef CONFIG_CPU_MIPSR6
 	/* We need to save hi/lo and restore them on the way out */
 	uasm_i_mfhi(&p, T0);
 	UASM_i_SW(&p, T0, offsetof(struct kvm_vcpu_arch, hi), K1);
 
 	uasm_i_mflo(&p, T0);
 	UASM_i_SW(&p, T0, offsetof(struct kvm_vcpu_arch, lo), K1);
+#endif
 
 	/* Finally save guest k1 to VCPU */
 	uasm_i_ehb(&p);
@@ -663,12 +661,6 @@ static void *kvm_mips_build_ret_to_host(void *addr)
 		UASM_i_LW(&p, i, offsetof(struct pt_regs, regs[i]), K1);
 	}
 
-	UASM_i_LW(&p, K0, offsetof(struct pt_regs, hi), K1);
-	uasm_i_mthi(&p, K0);
-
-	UASM_i_LW(&p, K0, offsetof(struct pt_regs, lo), K1);
-	uasm_i_mtlo(&p, K0);
-
 	/* Restore RDHWR access */
 	UASM_i_LA_mostly(&p, K0, (long)&hwrena);
 	uasm_i_lw(&p, K0, uasm_rel_lo((long)&hwrena), K0);

arch/mips/kvm/mips.c

@@ -521,8 +521,10 @@ static u64 kvm_mips_get_one_regs[] = {
 	KVM_REG_MIPS_R30,
 	KVM_REG_MIPS_R31,
 
+#ifndef CONFIG_CPU_MIPSR6
 	KVM_REG_MIPS_HI,
 	KVM_REG_MIPS_LO,
+#endif
 	KVM_REG_MIPS_PC,
 
 	KVM_REG_MIPS_CP0_INDEX,
@@ -666,12 +668,14 @@ static int kvm_mips_get_reg(struct kvm_vcpu *vcpu,
 	case KVM_REG_MIPS_R0 ... KVM_REG_MIPS_R31:
 		v = (long)vcpu->arch.gprs[reg->id - KVM_REG_MIPS_R0];
 		break;
+#ifndef CONFIG_CPU_MIPSR6
 	case KVM_REG_MIPS_HI:
 		v = (long)vcpu->arch.hi;
 		break;
 	case KVM_REG_MIPS_LO:
 		v = (long)vcpu->arch.lo;
 		break;
+#endif
 	case KVM_REG_MIPS_PC:
 		v = (long)vcpu->arch.pc;
 		break;
@@ -887,12 +891,14 @@ static int kvm_mips_set_reg(struct kvm_vcpu *vcpu,
 	case KVM_REG_MIPS_R1 ... KVM_REG_MIPS_R31:
 		vcpu->arch.gprs[reg->id - KVM_REG_MIPS_R0] = v;
 		break;
+#ifndef CONFIG_CPU_MIPSR6
 	case KVM_REG_MIPS_HI:
 		vcpu->arch.hi = v;
 		break;
 	case KVM_REG_MIPS_LO:
 		vcpu->arch.lo = v;
 		break;
+#endif
 	case KVM_REG_MIPS_PC:
 		vcpu->arch.pc = v;
 		break;