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: 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

1 files changed, 8 insertions, 0 deletions

diff --git a/arch/mips/include/asm/kvm_host.h b/arch/mips/include/asm/kvm_host.h
index f722b0528c25..8fc3ba2872f0 100644
--- a/arch/mips/include/asm/kvm_host.h
+++ b/arch/mips/include/asm/kvm_host.h
@@ -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);