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@xxxxxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Ralf Baechle <ralf@xxxxxxxxxxxxxx>
Cc: Gleb Natapov <gleb@xxxxxxxxxx>
Cc: kvm@xxxxxxxxxxxxxxx
Cc: linux-mips@xxxxxxxxxxxxxx
---
arch/mips/include/asm/kvm_host.h | 8 ++++++++
arch/mips/kvm/emulate.c | 36 ++++++++++++++++++++++++++++++++++++
arch/mips/kvm/mips.c | 7 +++++++
arch/mips/kvm/stats.c | 1 +
arch/mips/kvm/trap_emul.c | 19 +++++++++++++++++++
5 files changed, 71 insertions(+)
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);
diff --git a/arch/mips/kvm/emulate.c b/arch/mips/kvm/emulate.c
index 838d3a6a5b7d..33e132dc7de8 100644
--- 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 f5e7ddab02f7..399b5517ecb8 100644
--- 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 a74d6024c5ad..dd90b0a92181 100644
--- 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 4372cc86650c..dc019950e243 100644
--- 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,
--
2.0.5
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