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Commit 0a560427 authored by James Hogan's avatar James Hogan
Browse files

MIPS: KVM: Handle TRAP exceptions from guest kernel 



Trap instructions are used by Linux to implement BUG_ON(), however KVM
doesn't pass trap exceptions on to the guest if they occur in guest
kernel mode, instead triggering an internal error "Exception Code: 13,
not yet handled". The guest kernel then doesn't get a chance to print
the usual BUG message and stack trace.

Implement handling of the trap exception so that it gets passed to the
guest and the user is left with a more useful log message.

Signed-off-by: default avatarJames Hogan <james.hogan@imgtec.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Gleb Natapov <gleb@kernel.org>
Cc: kvm@vger.kernel.org
Cc: linux-mips@linux-mips.org
parent 64bedffe

arch/mips/include/asm/kvm_host.h

+8 −0
Original line number Diff line number Diff line
@@ -119,6 +119,7 @@ struct kvm_vcpu_stat { 
	u32 syscall_exits;

	u32 resvd_inst_exits;

	u32 break_inst_exits;

	u32 trap_inst_exits;

	u32 flush_dcache_exits;

	u32 halt_successful_poll;

	u32 halt_wakeup;
@@ -138,6 +139,7 @@ enum kvm_mips_exit_types { 
	SYSCALL_EXITS,

	RESVD_INST_EXITS,

	BREAK_INST_EXITS,

	TRAP_INST_EXITS,

	FLUSH_DCACHE_EXITS,

	MAX_KVM_MIPS_EXIT_TYPES

};
@@ -579,6 +581,7 @@ struct kvm_mips_callbacks { 
	int (*handle_syscall)(struct kvm_vcpu *vcpu);

	int (*handle_res_inst)(struct kvm_vcpu *vcpu);

	int (*handle_break)(struct kvm_vcpu *vcpu);

	int (*handle_trap)(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);
@@ -713,6 +716,11 @@ extern enum emulation_result kvm_mips_emulate_bp_exc(unsigned long cause, 
						     struct kvm_run *run,

						     struct kvm_vcpu *vcpu);



extern enum emulation_result kvm_mips_emulate_trap_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

+36 −0
Original line number Diff line number Diff line
@@ -1970,6 +1970,41 @@ enum emulation_result kvm_mips_emulate_bp_exc(unsigned long cause, 
	return er;

}



enum emulation_result kvm_mips_emulate_trap_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 TRAP @ pc %#lx\n", arch->pc);



		kvm_change_c0_guest_cause(cop0, (0xff),

					  (T_TRAP << CAUSEB_EXCCODE));



		/* Set PC to the exception entry point */

		arch->pc = KVM_GUEST_KSEG0 + 0x180;



	} else {

		kvm_err("Trying to deliver TRAP when EXL is already set\n");

		er = EMULATE_FAIL;

	}



	return er;

}



/* ll/sc, rdhwr, sync emulation */



#define OPCODE 0xfc000000
@@ -2176,6 +2211,7 @@ enum emulation_result kvm_mips_check_privilege(unsigned long cause, 
		case T_SYSCALL:

		case T_BREAK:

		case T_RES_INST:

		case T_TRAP:

		case T_MSADIS:

			break;

arch/mips/kvm/mips.c

+7 −0
Original line number Diff line number Diff line
@@ -48,6 +48,7 @@ struct kvm_stats_debugfs_item debugfs_entries[] = { 
	{ "syscall",	  VCPU_STAT(syscall_exits),	 KVM_STAT_VCPU },

	{ "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 },

	{ "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 },
@@ -1119,6 +1120,12 @@ int kvm_mips_handle_exit(struct kvm_run *run, struct kvm_vcpu *vcpu) 
		ret = kvm_mips_callbacks->handle_break(vcpu);

		break;



	case T_TRAP:

		++vcpu->stat.trap_inst_exits;

		trace_kvm_exit(vcpu, TRAP_INST_EXITS);

		ret = kvm_mips_callbacks->handle_trap(vcpu);

		break;



	case T_MSADIS:

		ret = kvm_mips_callbacks->handle_msa_disabled(vcpu);

		break;

arch/mips/kvm/stats.c

+1 −0
Original line number Diff line number Diff line
@@ -25,6 +25,7 @@ char *kvm_mips_exit_types_str[MAX_KVM_MIPS_EXIT_TYPES] = { 
	"System Call",

	"Reserved Inst",

	"Break Inst",

	"Trap Inst",

	"D-Cache Flushes",

};

arch/mips/kvm/trap_emul.c

+19 −0
Original line number Diff line number Diff line
@@ -330,6 +330,24 @@ static int kvm_trap_emul_handle_break(struct kvm_vcpu *vcpu) 
	return ret;

}



static int kvm_trap_emul_handle_trap(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_trap_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;
@@ -497,6 +515,7 @@ static struct kvm_mips_callbacks kvm_trap_emul_callbacks = { 
	.handle_syscall = kvm_trap_emul_handle_syscall,

	.handle_res_inst = kvm_trap_emul_handle_res_inst,

	.handle_break = kvm_trap_emul_handle_break,

	.handle_trap = kvm_trap_emul_handle_trap,

	.handle_msa_disabled = kvm_trap_emul_handle_msa_disabled,



	.vm_init = kvm_trap_emul_vm_init,