gdbstub, kvm: let KVM report supported singlestep flags

Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
[Extracted from Maxim's patch into a separate commit. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20211111110604.207376-5-pbonzini@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

accel/kvm/kvm-all.c

@@ -168,6 +168,8 @@ bool kvm_vm_attributes_allowed;
 bool kvm_direct_msi_allowed;
 bool kvm_ioeventfd_any_length_allowed;
 bool kvm_msi_use_devid;
+bool kvm_has_guest_debug;
+int kvm_sstep_flags;
 static bool kvm_immediate_exit;
 static hwaddr kvm_max_slot_size = ~0;
 
@@ -2564,6 +2566,16 @@ static int kvm_init(MachineState *ms)
     kvm_ioeventfd_any_length_allowed =
         (kvm_check_extension(s, KVM_CAP_IOEVENTFD_ANY_LENGTH) > 0);
 
+#ifdef KVM_CAP_SET_GUEST_DEBUG
+    kvm_has_guest_debug =
+        (kvm_check_extension(s, KVM_CAP_SET_GUEST_DEBUG) > 0);
+#endif
+
+    kvm_sstep_flags = 0;
+    if (kvm_has_guest_debug) {
+        kvm_sstep_flags = SSTEP_ENABLE;
+    }
+
     kvm_state = s;
 
     ret = kvm_arch_init(ms, s);

gdbstub.c

@@ -391,6 +391,8 @@ static void init_gdbserver_state(void)
      */
     if (replay_mode != REPLAY_MODE_NONE) {
         gdbserver_state.supported_sstep_flags = SSTEP_ENABLE;
+    } else if (kvm_enabled()) {
+        gdbserver_state.supported_sstep_flags = kvm_get_supported_sstep_flags();
     } else {
         gdbserver_state.supported_sstep_flags =
             SSTEP_ENABLE | SSTEP_NOIRQ | SSTEP_NOTIMER;
@@ -400,7 +402,8 @@ static void init_gdbserver_state(void)
      * By default use no IRQs and no timers while single stepping so as to
      * make single stepping like an ICE HW step.
      */
-    gdbserver_state.sstep_flags = gdbserver_state.supported_sstep_flags;
+    gdbserver_state.sstep_flags = SSTEP_ENABLE | SSTEP_NOIRQ | SSTEP_NOTIMER;
+    gdbserver_state.sstep_flags &= gdbserver_state.supported_sstep_flags;
 
 }
 
@@ -3520,6 +3523,11 @@ int gdbserver_start(const char *device)
         return -1;
     }
 
+    if (kvm_enabled() && !kvm_supports_guest_debug()) {
+        error_report("gdbstub: KVM doesn't support guest debugging");
+        return -1;
+    }
+
     if (!device)
         return -1;
     if (strcmp(device, "none") != 0) {

include/sysemu/kvm.h

@@ -46,6 +46,8 @@ extern bool kvm_readonly_mem_allowed;
 extern bool kvm_direct_msi_allowed;
 extern bool kvm_ioeventfd_any_length_allowed;
 extern bool kvm_msi_use_devid;
+extern bool kvm_has_guest_debug;
+extern int kvm_sstep_flags;
 
 #define kvm_enabled()           (kvm_allowed)
 /**
@@ -167,6 +169,17 @@ extern bool kvm_msi_use_devid;
  */
 #define kvm_msi_devid_required() (kvm_msi_use_devid)
 
+/*
+ * Does KVM support guest debugging
+ */
+#define kvm_supports_guest_debug() (kvm_has_guest_debug)
+
+/*
+ * kvm_supported_sstep_flags
+ * Returns: SSTEP_* flags that KVM supports for guest debug
+ */
+#define kvm_get_supported_sstep_flags() (kvm_sstep_flags)
+
 #else
 
 #define kvm_enabled()           (0)
@@ -184,6 +197,8 @@ extern bool kvm_msi_use_devid;
 #define kvm_direct_msi_enabled() (false)
 #define kvm_ioeventfd_any_length_enabled() (false)
 #define kvm_msi_devid_required() (false)
+#define kvm_supports_guest_debug() (false)
+#define kvm_get_supported_sstep_flags() (0)
 
 #endif  /* CONFIG_KVM_IS_POSSIBLE */