[PATCH 2/2] gdbstub: implement NOIRQ support for single step on KVM, when kvm's KVM_GUESTDBG_BLOCKIRQ debug flag is supported.

[Maxim Levitsky <mlevitsk@redhat.com>]

Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
---
 accel/kvm/kvm-all.c  | 25 +++++++++++++++++++
 gdbstub.c            | 59 ++++++++++++++++++++++++++++++++++++--------
 include/sysemu/kvm.h | 13 ++++++++++
 3 files changed, 87 insertions(+), 10 deletions(-)

diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
index b6d9f92f15..bc7955fb19 100644
--- a/accel/kvm/kvm-all.c
+++ b/accel/kvm/kvm-all.c
@@ -147,6 +147,8 @@ 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;
 
@@ -2186,6 +2188,25 @@ static int kvm_init(MachineState *ms)
     kvm_ioeventfd_any_length_allowed =
         (kvm_check_extension(s, KVM_CAP_IOEVENTFD_ANY_LENGTH) > 0);
 
+    kvm_has_guest_debug =
+        (kvm_check_extension(s, KVM_CAP_SET_GUEST_DEBUG) > 0);
+
+    kvm_sstep_flags = 0;
+
+    if (kvm_has_guest_debug) {
+        /* Assume that single stepping is supported */
+        kvm_sstep_flags = SSTEP_ENABLE;
+
+        int guest_debug_flags =
+            kvm_check_extension(s, KVM_CAP_SET_GUEST_DEBUG2);
+
+        if (guest_debug_flags > 0) {
+            if (guest_debug_flags & KVM_GUESTDBG_BLOCKIRQ) {
+                kvm_sstep_flags |= SSTEP_NOIRQ;
+            }
+        }
+    }
+
     kvm_state = s;
 
     ret = kvm_arch_init(ms, s);
@@ -2796,6 +2817,10 @@ int kvm_update_guest_debug(CPUState *cpu, unsigned long reinject_trap)
 
     if (cpu->singlestep_enabled) {
         data.dbg.control |= KVM_GUESTDBG_ENABLE | KVM_GUESTDBG_SINGLESTEP;
+
+        if (cpu->singlestep_enabled & SSTEP_NOIRQ) {
+            data.dbg.control |= KVM_GUESTDBG_BLOCKIRQ;
+        }
     }
     kvm_arch_update_guest_debug(cpu, &data.dbg);
 
diff --git a/gdbstub.c b/gdbstub.c
index 054665e93e..f789ded99d 100644
--- a/gdbstub.c
+++ b/gdbstub.c
@@ -369,12 +369,11 @@ typedef struct GDBState {
     gdb_syscall_complete_cb current_syscall_cb;
     GString *str_buf;
     GByteArray *mem_buf;
+    int sstep_flags;
+    int supported_sstep_flags;
 } GDBState;
 
-/* By default use no IRQs and no timers while single stepping so as to
- * make single stepping like an ICE HW step.
- */
-static int sstep_flags = SSTEP_ENABLE|SSTEP_NOIRQ|SSTEP_NOTIMER;
+static GDBState gdbserver_state;
 
 /* Retrieves flags for single step mode. */
 static int get_sstep_flags(void)
@@ -386,11 +385,10 @@ static int get_sstep_flags(void)
     if (replay_mode != REPLAY_MODE_NONE) {
         return SSTEP_ENABLE;
     } else {
-        return sstep_flags;
+        return gdbserver_state.sstep_flags;
     }
 }
 
-static GDBState gdbserver_state;
 
 static void init_gdbserver_state(void)
 {
@@ -400,6 +398,23 @@ static void init_gdbserver_state(void)
     gdbserver_state.str_buf = g_string_new(NULL);
     gdbserver_state.mem_buf = g_byte_array_sized_new(MAX_PACKET_LENGTH);
     gdbserver_state.last_packet = g_byte_array_sized_new(MAX_PACKET_LENGTH + 4);
+
+
+    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;
+    }
+
+    /*
+     * 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 = SSTEP_ENABLE | SSTEP_NOIRQ | SSTEP_NOTIMER;
+    gdbserver_state.sstep_flags &= gdbserver_state.supported_sstep_flags;
+
 }
 
 #ifndef CONFIG_USER_ONLY
@@ -2023,24 +2038,43 @@ static void handle_v_commands(GdbCmdContext *gdb_ctx, void *user_ctx)
 
 static void handle_query_qemu_sstepbits(GdbCmdContext *gdb_ctx, void *user_ctx)
 {
-    g_string_printf(gdbserver_state.str_buf, "ENABLE=%x,NOIRQ=%x,NOTIMER=%x",
-                    SSTEP_ENABLE, SSTEP_NOIRQ, SSTEP_NOTIMER);
+    g_string_printf(gdbserver_state.str_buf, "ENABLE=%x", SSTEP_ENABLE);
+
+    if (gdbserver_state.supported_sstep_flags & SSTEP_NOIRQ) {
+        g_string_append_printf(gdbserver_state.str_buf, ",NOIRQ=%x",
+                               SSTEP_NOIRQ);
+    }
+
+    if (gdbserver_state.supported_sstep_flags & SSTEP_NOTIMER) {
+        g_string_append_printf(gdbserver_state.str_buf, ",NOTIMER=%x",
+                               SSTEP_NOTIMER);
+    }
+
     put_strbuf();
 }
 
 static void handle_set_qemu_sstep(GdbCmdContext *gdb_ctx, void *user_ctx)
 {
+    int new_sstep_flags;
     if (!gdb_ctx->num_params) {
         return;
     }
 
-    sstep_flags = gdb_ctx->params[0].val_ul;
+    new_sstep_flags = gdb_ctx->params[0].val_ul;
+
+    if (new_sstep_flags  & ~gdbserver_state.supported_sstep_flags) {
+        put_packet("E22");
+        return;
+    }
+
+    gdbserver_state.sstep_flags = new_sstep_flags;
     put_packet("OK");
 }
 
 static void handle_query_qemu_sstep(GdbCmdContext *gdb_ctx, void *user_ctx)
 {
-    g_string_printf(gdbserver_state.str_buf, "0x%x", sstep_flags);
+    g_string_printf(gdbserver_state.str_buf, "0x%x",
+                    gdbserver_state.sstep_flags);
     put_strbuf();
 }
 
@@ -3499,6 +3533,11 @@ 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) {
diff --git a/include/sysemu/kvm.h b/include/sysemu/kvm.h
index a1ab1ee12d..42f9ce6344 100644
--- a/include/sysemu/kvm.h
+++ b/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)
-- 
2.26.2