target/riscv/cpu.c: restrict 'marchid' value

'marchid' shouldn't be set to a different value as previously set for
named CPUs.

For all other CPUs it shouldn't be freely set either - the spec requires
that 'marchid' can't have the MSB (most significant bit) set and every
other bit set to zero, i.e. 0x80000000 is an invalid 'marchid' value for
32 bit CPUs.

As with 'mimpid', setting a default value based on the current QEMU
version is not a good idea because it implies that the CPU
implementation changes from one QEMU version to the other. Named CPUs
should set 'marchid' to a meaningful value instead, and generic CPUs can
set to any valid value.

For the 'veyron-v1' CPU this is the error thrown if 'marchid' is set to
a different val:

$ ./build/qemu-system-riscv64 -M virt -nographic -cpu veyron-v1,marchid=0x80000000
qemu-system-riscv64: can't apply global veyron-v1-riscv-cpu.marchid=0x80000000:
    Unable to change veyron-v1-riscv-cpu marchid (0x8000000000010000)

And, for generics CPUs, this is the error when trying to set to an
invalid val:

$ ./build/qemu-system-riscv64 -M virt -nographic -cpu rv64,marchid=0x8000000000000000
qemu-system-riscv64: can't apply global rv64-riscv-cpu.marchid=0x8000000000000000:
    Unable to set marchid with MSB (64) bit set and the remaining bits zero

Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20230706101738.460804-6-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

target/riscv/cpu.c

@@ -39,11 +39,6 @@
 #include "tcg/tcg.h"
 
 /* RISC-V CPU definitions */
-
-#define RISCV_CPU_MARCHID   ((QEMU_VERSION_MAJOR << 16) | \
-                             (QEMU_VERSION_MINOR << 8)  | \
-                             (QEMU_VERSION_MICRO))
-
 static const char riscv_single_letter_exts[] = "IEMAFDQCPVH";
 
 struct isa_ext_data {
@@ -1811,8 +1806,6 @@ static void riscv_cpu_add_user_properties(Object *obj)
 static Property riscv_cpu_properties[] = {
     DEFINE_PROP_BOOL("debug", RISCVCPU, cfg.debug, true),
 
-    DEFINE_PROP_UINT64("marchid", RISCVCPU, cfg.marchid, RISCV_CPU_MARCHID),
-
 #ifndef CONFIG_USER_ONLY
     DEFINE_PROP_UINT64("resetvec", RISCVCPU, env.resetvec, DEFAULT_RSTVEC),
 #endif
@@ -1959,6 +1952,56 @@ static void cpu_get_mimpid(Object *obj, Visitor *v, const char *name,
     visit_type_bool(v, name, &value, errp);
 }
 
+static void cpu_set_marchid(Object *obj, Visitor *v, const char *name,
+                            void *opaque, Error **errp)
+{
+    bool dynamic_cpu = riscv_cpu_is_dynamic(obj);
+    RISCVCPU *cpu = RISCV_CPU(obj);
+    uint64_t prev_val = cpu->cfg.marchid;
+    uint64_t value, invalid_val;
+    uint32_t mxlen = 0;
+
+    if (!visit_type_uint64(v, name, &value, errp)) {
+        return;
+    }
+
+    if (!dynamic_cpu && prev_val != value) {
+        error_setg(errp, "Unable to change %s marchid (0x%" PRIu64 ")",
+                   object_get_typename(obj), prev_val);
+        return;
+    }
+
+    switch (riscv_cpu_mxl(&cpu->env)) {
+    case MXL_RV32:
+        mxlen = 32;
+        break;
+    case MXL_RV64:
+    case MXL_RV128:
+        mxlen = 64;
+        break;
+    default:
+        g_assert_not_reached();
+    }
+
+    invalid_val = 1LL << (mxlen - 1);
+
+    if (value == invalid_val) {
+        error_setg(errp, "Unable to set marchid with MSB (%u) bit set "
+                         "and the remaining bits zero", mxlen);
+        return;
+    }
+
+    cpu->cfg.marchid = value;
+}
+
+static void cpu_get_marchid(Object *obj, Visitor *v, const char *name,
+                           void *opaque, Error **errp)
+{
+    bool value = RISCV_CPU(obj)->cfg.marchid;
+
+    visit_type_bool(v, name, &value, errp);
+}
+
 static void riscv_cpu_class_init(ObjectClass *c, void *data)
 {
     RISCVCPUClass *mcc = RISCV_CPU_CLASS(c);
@@ -1996,6 +2039,9 @@ static void riscv_cpu_class_init(ObjectClass *c, void *data)
     object_class_property_add(c, "mimpid", "uint64", cpu_get_mimpid,
                               cpu_set_mimpid, NULL, NULL);
 
+    object_class_property_add(c, "marchid", "uint64", cpu_get_marchid,
+                              cpu_set_marchid, NULL, NULL);
+
     device_class_set_props(dc, riscv_cpu_properties);
 }