Xen was broken by commit 1583a3898853 ("cpus: extract out qtest-specific
code to accel/qtest").  Xen relied on qemu_init_vcpu() calling
qemu_dummy_start_vcpu() in the default case, but that was replaced by
g_assert_not_reached().

Add a minimal "CpusAccel" for xen using the dummy-cpu implementation
used by qtest.

Signed-off-by: Jason Andryuk <jandryuk@gmail.com>
---
 accel/dummy/meson.build |  1 +
 accel/xen/xen-all.c     | 10 ++++++++++
 2 files changed, 11 insertions(+)

diff --git a/accel/dummy/meson.build b/accel/dummy/meson.build
index 5fbe27de90..cdff0ba746 100644
--- a/accel/dummy/meson.build
+++ b/accel/dummy/meson.build
@@ -4,3 +4,4 @@ dummy_ss.add(files(
 ))
 
 specific_ss.add_all(when: ['CONFIG_SOFTMMU', 'CONFIG_POSIX'], if_true: dummy_ss)
+specific_ss.add_all(when: ['CONFIG_XEN'], if_true: dummy_ss)
diff --git a/accel/xen/xen-all.c b/accel/xen/xen-all.c
index 60b971d0a8..2d243c58d4 100644
--- a/accel/xen/xen-all.c
+++ b/accel/xen/xen-all.c
@@ -16,12 +16,15 @@
 #include "hw/xen/xen_pt.h"
 #include "chardev/char.h"
 #include "sysemu/accel.h"
+#include "sysemu/cpus.h"
 #include "sysemu/xen.h"
 #include "sysemu/runstate.h"
 #include "migration/misc.h"
 #include "migration/global_state.h"
 #include "hw/boards.h"
 
+#include "accel/dummy/dummy-cpus.h"
+
 //#define DEBUG_XEN
 
 #ifdef DEBUG_XEN
@@ -153,6 +156,10 @@ static void xen_setup_post(MachineState *ms, AccelState *accel)
     }
 }
 
+const CpusAccel xen_cpus = {
+    .create_vcpu_thread = dummy_start_vcpu_thread,
+};
+
 static int xen_init(MachineState *ms)
 {
     MachineClass *mc = MACHINE_GET_CLASS(ms);
@@ -180,6 +187,9 @@ static int xen_init(MachineState *ms)
      * opt out of system RAM being allocated by generic code
      */
     mc->default_ram_id = NULL;
+
+    cpus_register_accel(&xen_cpus);
+
     return 0;
 }
 
-- 
2.25.1

On 10/12/20 10:07 PM, Jason Andryuk wrote:
> Xen was broken by commit 1583a3898853 ("cpus: extract out qtest-specific
> code to accel/qtest").  Xen relied on qemu_init_vcpu() calling
> qemu_dummy_start_vcpu() in the default case, but that was replaced by
> g_assert_not_reached().
> 
> Add a minimal "CpusAccel" for xen using the dummy-cpu implementation
> used by qtest.
> 
> Signed-off-by: Jason Andryuk <jandryuk@gmail.com>
> ---
>  accel/dummy/meson.build |  1 +
>  accel/xen/xen-all.c     | 10 ++++++++++
>  2 files changed, 11 insertions(+)
> 
> diff --git a/accel/dummy/meson.build b/accel/dummy/meson.build
> index 5fbe27de90..cdff0ba746 100644
> --- a/accel/dummy/meson.build
> +++ b/accel/dummy/meson.build
> @@ -4,3 +4,4 @@ dummy_ss.add(files(
>  ))
>  
>  specific_ss.add_all(when: ['CONFIG_SOFTMMU', 'CONFIG_POSIX'], if_true: dummy_ss)
> +specific_ss.add_all(when: ['CONFIG_XEN'], if_true: dummy_ss)
> diff --git a/accel/xen/xen-all.c b/accel/xen/xen-all.c
> index 60b971d0a8..2d243c58d4 100644
> --- a/accel/xen/xen-all.c
> +++ b/accel/xen/xen-all.c
> @@ -16,12 +16,15 @@
>  #include "hw/xen/xen_pt.h"
>  #include "chardev/char.h"
>  #include "sysemu/accel.h"
> +#include "sysemu/cpus.h"
>  #include "sysemu/xen.h"
>  #include "sysemu/runstate.h"
>  #include "migration/misc.h"
>  #include "migration/global_state.h"
>  #include "hw/boards.h"
>  
> +#include "accel/dummy/dummy-cpus.h"

it seems this should be in includes/sysemu/accel.h or so.

> +
>  //#define DEBUG_XEN
>  
>  #ifdef DEBUG_XEN
> @@ -153,6 +156,10 @@ static void xen_setup_post(MachineState *ms, AccelState *accel)
>      }
>  }
>  
> +const CpusAccel xen_cpus = {
> +    .create_vcpu_thread = dummy_start_vcpu_thread,
> +};
> +
>  static int xen_init(MachineState *ms)
>  {
>      MachineClass *mc = MACHINE_GET_CLASS(ms);
> @@ -180,6 +187,9 @@ static int xen_init(MachineState *ms)
>       * opt out of system RAM being allocated by generic code
>       */
>      mc->default_ram_id = NULL;
> +
> +    cpus_register_accel(&xen_cpus);
> +
>      return 0;
>  }
>  
> 

Ciao,

Claudio