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

diff --git a/arch/mips/include/asm/kvm_host.h b/arch/mips/include/asm/kvm_host.h
index f722b0528c25280d62139fb51756dca8690029b2..8fc3ba2872f00bb1e67ab5c60e7921b7ef9aac82 100644 (file)
--- 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);
 

diff --git a/arch/mips/kvm/emulate.c b/arch/mips/kvm/emulate.c
index 838d3a6a5b7dd5d03cd9d968359bca1be84d1910..33e132dc7de813bd60818a21cd5955cb67624ebd 100644 (file)
--- a/arch/mips/kvm/emulate.c
+++ b/arch/mips/kvm/emulate.c
@@ -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;
 

diff --git a/arch/mips/kvm/mips.c b/arch/mips/kvm/mips.c
index f5e7ddab02f73d3860857d0052f7c1bb0c10fb65..399b5517ecb8042819b6b457edfd33d1ab7cc2f8 100644 (file)
--- a/arch/mips/kvm/mips.c
+++ b/arch/mips/kvm/mips.c
@@ -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;

diff --git a/arch/mips/kvm/stats.c b/arch/mips/kvm/stats.c
index a74d6024c5ad5f5c7e0701a309e246bd42532992..dd90b0a9218183f8601911fcc8d8256c8edc0118 100644 (file)
--- a/arch/mips/kvm/stats.c
+++ b/arch/mips/kvm/stats.c
@@ -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",
 };
 

diff --git a/arch/mips/kvm/trap_emul.c b/arch/mips/kvm/trap_emul.c
index 4372cc86650ce3dd0b3a7c8d4d882e5f790c1c66..dc019950e243a9518ebb9ed75a9f2bdb1b97eb49 100644 (file)
--- a/arch/mips/kvm/trap_emul.c
+++ b/arch/mips/kvm/trap_emul.c
@@ -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,