kvm: Improve reporting of fatal errors

Report KVM_EXIT_UNKNOWN, KVM_EXIT_FAIL_ENTRY, and KVM_EXIT_EXCEPTION
with more details to stderr. The latter two are so far x86-only, so move
them into the arch-specific handler. Integrate the Intel real mode
warning on KVM_EXIT_FAIL_ENTRY that qemu-kvm carries, but actually
restrict it to Intel CPUs. Moreover, always dump the CPU state in case
we fail.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

kvm-all.c

@@ -817,22 +817,22 @@ static int kvm_handle_io(uint16_t port, void *data, int direction, int size,
 #ifdef KVM_CAP_INTERNAL_ERROR_DATA
 static int kvm_handle_internal_error(CPUState *env, struct kvm_run *run)
 {
-
+    fprintf(stderr, "KVM internal error.");
     if (kvm_check_extension(kvm_state, KVM_CAP_INTERNAL_ERROR_DATA)) {
         int i;
 
-        fprintf(stderr, "KVM internal error. Suberror: %d\n",
+        fprintf(stderr, " Suberror: %d\n", run->internal.suberror);
-                run->internal.suberror);
-
         for (i = 0; i < run->internal.ndata; ++i) {
             fprintf(stderr, "extra data[%d]: %"PRIx64"\n",
                     i, (uint64_t)run->internal.data[i]);
         }
+    } else {
+        fprintf(stderr, "\n");
     }
-    cpu_dump_state(env, stderr, fprintf, 0);
     if (run->internal.suberror == KVM_INTERNAL_ERROR_EMULATION) {
         fprintf(stderr, "emulation failure\n");
         if (!kvm_arch_stop_on_emulation_error(env)) {
+            cpu_dump_state(env, stderr, fprintf, 0);
             return 0;
         }
     }
@@ -966,15 +966,8 @@ int kvm_cpu_exec(CPUState *env)
             ret = 1;
             break;
         case KVM_EXIT_UNKNOWN:
-            DPRINTF("kvm_exit_unknown\n");
+            fprintf(stderr, "KVM: unknown exit, hardware reason %" PRIx64 "\n",
-            ret = -1;
+                    (uint64_t)run->hw.hardware_exit_reason);
-            break;
-        case KVM_EXIT_FAIL_ENTRY:
-            DPRINTF("kvm_exit_fail_entry\n");
-            ret = -1;
-            break;
-        case KVM_EXIT_EXCEPTION:
-            DPRINTF("kvm_exit_exception\n");
             ret = -1;
             break;
 #ifdef KVM_CAP_INTERNAL_ERROR_DATA
@@ -1001,6 +994,7 @@ int kvm_cpu_exec(CPUState *env)
     } while (ret > 0);
 
     if (ret < 0) {
+        cpu_dump_state(env, stderr, fprintf, 0);
         vm_stop(0);
         env->exit_request = 1;
     }

target-i386/cpu.h

@@ -874,6 +874,8 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count,
                    uint32_t *ecx, uint32_t *edx);
 int cpu_x86_register (CPUX86State *env, const char *cpu_model);
 void cpu_clear_apic_feature(CPUX86State *env);
+void host_cpuid(uint32_t function, uint32_t count,
+                uint32_t *eax, uint32_t *ebx, uint32_t *ecx, uint32_t *edx);
 
 /* helper.c */
 int cpu_x86_handle_mmu_fault(CPUX86State *env, target_ulong addr,

target-i386/cpuid.c

@@ -103,9 +103,8 @@ typedef struct model_features_t {
 int check_cpuid = 0;
 int enforce_cpuid = 0;
 
-static void host_cpuid(uint32_t function, uint32_t count,
+void host_cpuid(uint32_t function, uint32_t count,
-                       uint32_t *eax, uint32_t *ebx,
+                uint32_t *eax, uint32_t *ebx, uint32_t *ecx, uint32_t *edx)
-                       uint32_t *ecx, uint32_t *edx)
 {
 #if defined(CONFIG_KVM)
     uint32_t vec[4];

target-i386/kvm.c

@@ -1525,8 +1525,19 @@ static int kvm_handle_halt(CPUState *env)
     return 1;
 }
 
+static bool host_supports_vmx(void)
+{
+    uint32_t ecx, unused;
+
+    host_cpuid(1, 0, &unused, &unused, &ecx, &unused);
+    return ecx & CPUID_EXT_VMX;
+}
+
+#define VMX_INVALID_GUEST_STATE 0x80000021
+
 int kvm_arch_handle_exit(CPUState *env, struct kvm_run *run)
 {
+    uint64_t code;
     int ret = 0;
 
     switch (run->exit_reason) {
@@ -1537,6 +1548,28 @@ int kvm_arch_handle_exit(CPUState *env, struct kvm_run *run)
     case KVM_EXIT_SET_TPR:
         ret = 1;
         break;
+    case KVM_EXIT_FAIL_ENTRY:
+        code = run->fail_entry.hardware_entry_failure_reason;
+        fprintf(stderr, "KVM: entry failed, hardware error 0x%" PRIx64 "\n",
+                code);
+        if (host_supports_vmx() && code == VMX_INVALID_GUEST_STATE) {
+            fprintf(stderr,
+                    "\nIf you're runnning a guest on an Intel machine without "
+                        "unrestricted mode\n"
+                    "support, the failure can be most likely due to the guest "
+                        "entering an invalid\n"
+                    "state for Intel VT. For example, the guest maybe running "
+                        "in big real mode\n"
+                    "which is not supported on less recent Intel processors."
+                        "\n\n");
+        }
+        ret = -1;
+        break;
+    case KVM_EXIT_EXCEPTION:
+        fprintf(stderr, "KVM: exception %d exit (error code 0x%x)\n",
+                run->ex.exception, run->ex.error_code);
+        ret = -1;
+        break;
     default:
         fprintf(stderr, "KVM: unknown exit reason %d\n", run->exit_reason);
         ret = -1;