target/riscv: add riscv_cpu_accelerator_compatible()

Add an API to check if a given CPU is compatible with the current
accelerator.

This will allow query-cpu-model-expansion to work properly in conditions
where QEMU supports both accelerators (TCG and KVM), QEMU is then
launched using TCG, and the API requests information about a KVM only
CPU (e.g. 'host' CPU).

KVM doesn't have such restrictions and, at least in theory, all CPUs
models should work with KVM. We will revisit this API in case we decide
to restrict the amount of KVM CPUs we support.

Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20231018195638.211151-6-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

target/riscv/cpu.c

@@ -1063,6 +1063,15 @@ static void riscv_cpu_realize(DeviceState *dev, Error **errp)
     mcc->parent_realize(dev, errp);
 }
 
+bool riscv_cpu_accelerator_compatible(RISCVCPU *cpu)
+{
+    if (tcg_enabled()) {
+        return riscv_cpu_tcg_compatible(cpu);
+    }
+
+    return true;
+}
+
 #ifndef CONFIG_USER_ONLY
 static void cpu_riscv_get_satp(Object *obj, Visitor *v, const char *name,
                                void *opaque, Error **errp)

target/riscv/cpu.h

@@ -758,6 +758,7 @@ char *riscv_cpu_get_name(RISCVCPU *cpu);
 
 void riscv_cpu_finalize_features(RISCVCPU *cpu, Error **errp);
 void riscv_add_satp_mode_properties(Object *obj);
+bool riscv_cpu_accelerator_compatible(RISCVCPU *cpu);
 
 /* CSR function table */
 extern riscv_csr_operations csr_ops[CSR_TABLE_SIZE];

target/riscv/tcg/tcg-cpu.c

@@ -581,6 +581,11 @@ void riscv_tcg_cpu_finalize_features(RISCVCPU *cpu, Error **errp)
     }
 }
 
+bool riscv_cpu_tcg_compatible(RISCVCPU *cpu)
+{
+    return object_dynamic_cast(OBJECT(cpu), TYPE_RISCV_CPU_HOST) == NULL;
+}
+
 static bool riscv_cpu_is_generic(Object *cpu_obj)
 {
     return object_dynamic_cast(cpu_obj, TYPE_RISCV_DYNAMIC_CPU) != NULL;
@@ -598,7 +603,7 @@ static bool tcg_cpu_realize(CPUState *cs, Error **errp)
     RISCVCPU *cpu = RISCV_CPU(cs);
     Error *local_err = NULL;
 
-    if (object_dynamic_cast(OBJECT(cpu), TYPE_RISCV_CPU_HOST)) {
+    if (!riscv_cpu_tcg_compatible(cpu)) {
         g_autofree char *name = riscv_cpu_get_name(cpu);
         error_setg(errp, "'%s' CPU is not compatible with TCG acceleration",
                    name);

target/riscv/tcg/tcg-cpu.h

@@ -24,5 +24,6 @@
 
 void riscv_cpu_validate_set_extensions(RISCVCPU *cpu, Error **errp);
 void riscv_tcg_cpu_finalize_features(RISCVCPU *cpu, Error **errp);
+bool riscv_cpu_tcg_compatible(RISCVCPU *cpu);
 
 #endif