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MIPS: KVM: Handle TRAP exceptions from guest kernel

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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: James 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
This commit is contained in:
James Hogan 2015-02-06 16:03:57 +00:00
parent 64bedffe49
commit 0a5604272d
5 changed files with 71 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
arch/mips/include/asm/kvm_host.h
View File

@ -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);

36
arch/mips/kvm/emulate.c
View File

@ -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;

7
arch/mips/kvm/mips.c
View File

@ -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;

1
arch/mips/kvm/stats.c
View File

@ -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",
};

19
arch/mips/kvm/trap_emul.c
View File

@ -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,