target/riscv/cpu.c: check priv_ver before auto-enable zca/zcd/zcf

Commit bd30559 made changes in how we're checking and disabling
extensions based on env->priv_ver. One of the changes was to move the
extension disablement code to the end of realize(), being able to
disable extensions after we've auto-enabled some of them.

An unfortunate side effect of this change started to happen with CPUs
that has an older priv version, like sifive-u54. Starting on commit
2288a5c we're auto-enabling zca, zcd and zcf if RVC is enabled,
but these extensions are priv version 1.12.0. When running a cpu that
has an older priv ver (like sifive-u54) the user is spammed with
warnings like these:

qemu-system-riscv64: warning: disabling zca extension for hart 0x0000000000000000 because privilege spec version does not match
qemu-system-riscv64: warning: disabling zcd extension for hart 0x0000000000000000 because privilege spec version does not match

The warnings are part of the code that disables the extension, but in this
case we're throwing user warnings for stuff that we enabled on our own,
without user intervention. Users are left wondering what they did wrong.

A quick 8.1 fix for this nuisance is to check the CPU priv spec before
auto-enabling zca/zcd/zcf. A more appropriate fix will include a more
robust framework that will account for both priv_ver and user choice
when auto-enabling/disabling extensions, but for 8.1 we'll make it do
with this simple check.

It's also worth noticing that this is the only case where we're
auto-enabling extensions based on a criteria (in this case RVC) that
doesn't match the priv spec of the extensions we're enabling. There's no
need for more 8.1 band-aids.

Cc: Conor Dooley <conor@kernel.org>
Fixes: 2288a5c ("target/riscv: add cfg properties for Zc* extension")
Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Weiwei Li <liweiwei@iscas.ac.cn>
Tested-by: Conor Dooley <conor.dooley@microchip.com>
Message-Id: <20230717154141.60898-1-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

target/riscv/cpu.c

@@ -1225,7 +1225,8 @@ void riscv_cpu_validate_set_extensions(RISCVCPU *cpu, Error **errp)
         }
     }
 
-    if (riscv_has_ext(env, RVC)) {
+    /* 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;
         if (riscv_has_ext(env, RVF) && env->misa_mxl_max == MXL_RV32) {
             cpu->cfg.ext_zcf = true;