target/riscv/cpu.c: introduce cpu_cfg_ext_auto_update()

During realize() time we're activating a lot of extensions based on some
criteria, e.g.:

    if (cpu->cfg.ext_zk) {
        cpu->cfg.ext_zkn = true;
        cpu->cfg.ext_zkr = true;
        cpu->cfg.ext_zkt = true;
    }

This practice resulted in at least one case where we ended up enabling
something we shouldn't: RVC enabling zca/zcd/zcf when using a CPU that
has priv_spec older than 1.12.0.

We're also not considering user choice. There's no way of doing it now
but this is about to change in the next few patches.

cpu_cfg_ext_auto_update() will check for priv version mismatches before
enabling extensions. If we have a mismatch between the current priv
version and the extension we want to enable, do not enable it. In the
near future, this same function will also consider user choice when
deciding if we're going to enable/disable an extension or not.

For now let's use it to handle zca/zcd/zcf enablement if RVC is enabled.

Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Message-ID: <20230901194627.1214811-16-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

target/riscv/cpu.c

@@ -177,6 +177,43 @@ static void isa_ext_update_enabled(RISCVCPU *cpu, uint32_t ext_offset,
     *ext_enabled = en;
 }
 
+static int cpu_cfg_ext_get_min_version(uint32_t ext_offset)
+{
+    int i;
+
+    for (i = 0; i < ARRAY_SIZE(isa_edata_arr); i++) {
+        if (isa_edata_arr[i].ext_enable_offset != ext_offset) {
+            continue;
+        }
+
+        return isa_edata_arr[i].min_version;
+    }
+
+    g_assert_not_reached();
+}
+
+static void cpu_cfg_ext_auto_update(RISCVCPU *cpu, uint32_t ext_offset,
+                                    bool value)
+{
+    CPURISCVState *env = &cpu->env;
+    bool prev_val = isa_ext_is_enabled(cpu, ext_offset);
+    int min_version;
+
+    if (prev_val == value) {
+        return;
+    }
+
+    if (value && env->priv_ver != PRIV_VERSION_LATEST) {
+        /* Do not enable it if priv_ver is older than min_version */
+        min_version = cpu_cfg_ext_get_min_version(ext_offset);
+        if (env->priv_ver < min_version) {
+            return;
+        }
+    }
+
+    isa_ext_update_enabled(cpu, ext_offset, value);
+}
+
 const char * const riscv_int_regnames[] = {
     "x0/zero", "x1/ra",  "x2/sp",  "x3/gp",  "x4/tp",  "x5/t0",   "x6/t1",
     "x7/t2",   "x8/s0",  "x9/s1",  "x10/a0", "x11/a1", "x12/a2",  "x13/a3",
@@ -1268,12 +1305,12 @@ void riscv_cpu_validate_set_extensions(RISCVCPU *cpu, Error **errp)
 
     /* zca, zcd and zcf has a PRIV 1.12.0 restriction */
     if (riscv_has_ext(env, RVC) && env->priv_ver >= PRIV_VERSION_1_12_0) {
-        cpu->cfg.ext_zca = true;
+        cpu_cfg_ext_auto_update(cpu, CPU_CFG_OFFSET(ext_zca), true);
         if (riscv_has_ext(env, RVF) && env->misa_mxl_max == MXL_RV32) {
-            cpu->cfg.ext_zcf = true;
+            cpu_cfg_ext_auto_update(cpu, CPU_CFG_OFFSET(ext_zcf), true);
         }
         if (riscv_has_ext(env, RVD)) {
-            cpu->cfg.ext_zcd = true;
+            cpu_cfg_ext_auto_update(cpu, CPU_CFG_OFFSET(ext_zcd), true);
         }
     }