MIPS: KVM: Add FP exception handling

Add guest exception handling for floating point exceptions and
coprocessor 1 unusable exceptions.

Floating point exceptions from the guest need passing to the guest
kernel, so for these a guest FPE is emulated.

Also, coprocessor 1 unusable exceptions are normally passed straight
through to the guest (because no guest FPU was supported), but the
hypervisor can now handle them if the guest has its FPU enabled by
restoring the guest FPU context and enabling the FPU.

Signed-off-by: James Hogan <[e-mail]>
Cc: Paolo Bonzini <[e-mail]>
Cc: Paul Burton <[e-mail]>
Cc: Ralf Baechle <[e-mail]>
Cc: Gleb Natapov <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]

arch/mips/include/asm/kvm_host.h

···
 	u32 resvd_inst_exits;
 	u32 break_inst_exits;
 	u32 trap_inst_exits;
+	u32 fpe_exits;
 	u32 flush_dcache_exits;
 	u32 halt_successful_poll;
 	u32 halt_wakeup;
···
 	RESVD_INST_EXITS,
 	BREAK_INST_EXITS,
 	TRAP_INST_EXITS,
+	FPE_EXITS,
 	FLUSH_DCACHE_EXITS,
 	MAX_KVM_MIPS_EXIT_TYPES
 };
···
 	int (*handle_res_inst)(struct kvm_vcpu *vcpu);
 	int (*handle_break)(struct kvm_vcpu *vcpu);
 	int (*handle_trap)(struct kvm_vcpu *vcpu);
+	int (*handle_fpe)(struct kvm_vcpu *vcpu);
 	int (*handle_msa_disabled)(struct kvm_vcpu *vcpu);
 	int (*vm_init)(struct kvm *kvm);
 	int (*vcpu_init)(struct kvm_vcpu *vcpu);
···
 						       uint32_t *opc,
 						       struct kvm_run *run,
 						       struct kvm_vcpu *vcpu);
+
+extern enum emulation_result kvm_mips_emulate_fpe_exc(unsigned long cause,
+						      uint32_t *opc,
+						      struct kvm_run *run,
+						      struct kvm_vcpu *vcpu);
 
 extern enum emulation_result kvm_mips_complete_mmio_load(struct kvm_vcpu *vcpu,
 							 struct kvm_run *run);

arch/mips/kvm/emulate.c

···
 	return er;
 }
 
+enum emulation_result kvm_mips_emulate_fpe_exc(unsigned long cause,
+					       uint32_t *opc,
+					       struct kvm_run *run,
+					       struct kvm_vcpu *vcpu)
+{
+	struct mips_coproc *cop0 = vcpu->arch.cop0;
+	struct kvm_vcpu_arch *arch = &vcpu->arch;
+	enum emulation_result er = EMULATE_DONE;
+
+	if ((kvm_read_c0_guest_status(cop0) & ST0_EXL) == 0) {
+		/* save old pc */
+		kvm_write_c0_guest_epc(cop0, arch->pc);
+		kvm_set_c0_guest_status(cop0, ST0_EXL);
+
+		if (cause & CAUSEF_BD)
+			kvm_set_c0_guest_cause(cop0, CAUSEF_BD);
+		else
+			kvm_clear_c0_guest_cause(cop0, CAUSEF_BD);
+
+		kvm_debug("Delivering FPE @ pc %#lx\n", arch->pc);
+
+		kvm_change_c0_guest_cause(cop0, (0xff),
+					  (T_FPE << CAUSEB_EXCCODE));
+
+		/* Set PC to the exception entry point */
+		arch->pc = KVM_GUEST_KSEG0 + 0x180;
+
+	} else {
+		kvm_err("Trying to deliver FPE when EXL is already set\n");
+		er = EMULATE_FAIL;
+	}
+
+	return er;
+}
+
 /* ll/sc, rdhwr, sync emulation */
 
 #define OPCODE 0xfc000000
···
 		case T_BREAK:
 		case T_RES_INST:
 		case T_TRAP:
+		case T_FPE:
 		case T_MSADIS:
 			break;
 

arch/mips/kvm/mips.c

···
 	{ "resvd_inst",	  VCPU_STAT(resvd_inst_exits),	 KVM_STAT_VCPU },
 	{ "break_inst",	  VCPU_STAT(break_inst_exits),	 KVM_STAT_VCPU },
 	{ "trap_inst",	  VCPU_STAT(trap_inst_exits),	 KVM_STAT_VCPU },
+	{ "fpe",	  VCPU_STAT(fpe_exits),		 KVM_STAT_VCPU },
 	{ "flush_dcache", VCPU_STAT(flush_dcache_exits), KVM_STAT_VCPU },
 	{ "halt_successful_poll", VCPU_STAT(halt_successful_poll), KVM_STAT_VCPU },
 	{ "halt_wakeup",  VCPU_STAT(halt_wakeup),	 KVM_STAT_VCPU },
···
 		++vcpu->stat.trap_inst_exits;
 		trace_kvm_exit(vcpu, TRAP_INST_EXITS);
 		ret = kvm_mips_callbacks->handle_trap(vcpu);
+		break;
+
+	case T_FPE:
+		++vcpu->stat.fpe_exits;
+		trace_kvm_exit(vcpu, FPE_EXITS);
+		ret = kvm_mips_callbacks->handle_fpe(vcpu);
 		break;
 
 	case T_MSADIS:

arch/mips/kvm/stats.c

···
 	"Reserved Inst",
 	"Break Inst",
 	"Trap Inst",
+	"FPE",
 	"D-Cache Flushes",
 };
 

arch/mips/kvm/trap_emul.c

···
 
 static int kvm_trap_emul_handle_cop_unusable(struct kvm_vcpu *vcpu)
 {
+	struct mips_coproc *cop0 = vcpu->arch.cop0;
 	struct kvm_run *run = vcpu->run;
 	uint32_t __user *opc = (uint32_t __user *) vcpu->arch.pc;
 	unsigned long cause = vcpu->arch.host_cp0_cause;
 	enum emulation_result er = EMULATE_DONE;
 	int ret = RESUME_GUEST;
 
-	if (((cause & CAUSEF_CE) >> CAUSEB_CE) == 1)
-		er = kvm_mips_emulate_fpu_exc(cause, opc, run, vcpu);
-	else
+	if (((cause & CAUSEF_CE) >> CAUSEB_CE) == 1) {
+		/* FPU Unusable */
+		if (!kvm_mips_guest_has_fpu(&vcpu->arch) ||
+		    (kvm_read_c0_guest_status(cop0) & ST0_CU1) == 0) {
+			/*
+			 * Unusable/no FPU in guest:
+			 * deliver guest COP1 Unusable Exception
+			 */
+			er = kvm_mips_emulate_fpu_exc(cause, opc, run, vcpu);
+		} else {
+			/* Restore FPU state */
+			kvm_own_fpu(vcpu);
+			er = EMULATE_DONE;
+		}
+	} else {
 		er = kvm_mips_emulate_inst(cause, opc, run, vcpu);
+	}
 
 	switch (er) {
 	case EMULATE_DONE:
···
 	return ret;
 }
 
+static int kvm_trap_emul_handle_fpe(struct kvm_vcpu *vcpu)
+{
+	struct kvm_run *run = vcpu->run;
+	uint32_t __user *opc = (uint32_t __user *)vcpu->arch.pc;
+	unsigned long cause = vcpu->arch.host_cp0_cause;
+	enum emulation_result er = EMULATE_DONE;
+	int ret = RESUME_GUEST;
+
+	er = kvm_mips_emulate_fpe_exc(cause, opc, run, vcpu);
+	if (er == EMULATE_DONE) {
+		ret = RESUME_GUEST;
+	} else {
+		run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
+		ret = RESUME_HOST;
+	}
+	return ret;
+}
+
 static int kvm_trap_emul_handle_msa_disabled(struct kvm_vcpu *vcpu)
 {
 	struct kvm_run *run = vcpu->run;
···
 	.handle_res_inst = kvm_trap_emul_handle_res_inst,
 	.handle_break = kvm_trap_emul_handle_break,
 	.handle_trap = kvm_trap_emul_handle_trap,
+	.handle_fpe = kvm_trap_emul_handle_fpe,
 	.handle_msa_disabled = kvm_trap_emul_handle_msa_disabled,
 
 	.vm_init = kvm_trap_emul_vm_init,