Some CPUs need to check the requested features are compatible
with the requested accelerator. This has to be done *before*
the accelerator realizes a vCPU.
Introduce the verify_accel_features() handler and call it
just before accel_cpu_realizefn().

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
---
 include/hw/core/cpu.h | 4 ++++
 cpu.c                 | 5 +++++
 2 files changed, 9 insertions(+)

diff --git a/include/hw/core/cpu.h b/include/hw/core/cpu.h
index c90cf3a162..1e940f6bb5 100644
--- a/include/hw/core/cpu.h
+++ b/include/hw/core/cpu.h
@@ -103,6 +103,9 @@ struct SysemuCPUOps;
  * @class_by_name: Callback to map -cpu command line model name to an
  * instantiatable CPU type.
  * @parse_features: Callback to parse command line arguments.
+ * @verify_accel_features: Callback to verify if all requested CPU are
+ *        compatible with the requested accelerator. Called before the
+ *        accelerator realize a vCPU.
  * @reset_dump_flags: #CPUDumpFlags to use for reset logging.
  * @has_work: Callback for checking if there is work to do.
  * @memory_rw_debug: Callback for GDB memory access.
@@ -183,6 +186,7 @@ struct CPUClass {
      * class data that depends on the accelerator, see accel/accel-common.c.
      */
     void (*init_accel_cpu)(struct AccelCPUClass *accel_cpu, CPUClass *cc);
+    bool (*verify_accel_features)(CPUState *cs, Error **errp);
 
     /*
      * Keep non-pointer data at the end to minimize holes.
diff --git a/cpu.c b/cpu.c
index 0769b0b153..84b03c09ac 100644
--- a/cpu.c
+++ b/cpu.c
@@ -136,6 +136,11 @@ void cpu_exec_realizefn(CPUState *cpu, Error **errp)
     /* cache the cpu class for the hotpath */
     cpu->cc = CPU_GET_CLASS(cpu);
 
+    if (cpu->cc->verify_accel_features
+        && !cpu->cc->verify_accel_features(cpu, errp)) {
+        return false;
+    }
+
     if (!accel_cpu_realizefn(cpu, errp)) {
         return;
     }
-- 
2.41.0

On 9/18/23 09:02, Philippe Mathieu-Daudé wrote:
> Some CPUs need to check the requested features are compatible
> with the requested accelerator. This has to be done*before*
> the accelerator realizes a vCPU.
> Introduce the verify_accel_features() handler and call it
> just before accel_cpu_realizefn().
> 
> Signed-off-by: Philippe Mathieu-Daudé<philmd@linaro.org>
> ---
>   include/hw/core/cpu.h | 4 ++++
>   cpu.c                 | 5 +++++
>   2 files changed, 9 insertions(+)

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

r~