target/riscv: fix wfi exception behavior

The wfi exception trigger behavior should take into account user mode,
hstatus.vtw, and the fact the an wfi might raise different types of
exceptions depending on various factors:

If supervisor mode is not present:

- an illegal instruction exception should be generated if user mode
executes and wfi instruction and mstatus.tw = 1.

If supervisor mode is present:

- when a wfi instruction is executed, an illegal exception should be triggered
if either the current mode is user or the mode is supervisor and mstatus.tw is
set.

Plus, if the hypervisor extensions are enabled:

- a virtual instruction exception should be raised when a wfi is executed from
virtual-user or virtual-supervisor and hstatus.vtw is set.

Signed-off-by: Jose Martins <[email protected]>
Reviewed-by: Alistair Francis <[email protected]>
Message-id: [email protected]
Signed-off-by: Alistair Francis <[email protected]>

qemu/target/riscv/cpu_bits.h

@@ -427,6 +427,7 @@
 #define HSTATUS_SP2P         0x00000100
 #define HSTATUS_SP2V         0x00000200
 #define HSTATUS_VTVM         0x00100000
+#define HSTATUS_VTW          0x00200000
 #define HSTATUS_VTSR         0x00400000
 
 #define HSTATUS32_WPRI       0xFF8FF87E

qemu/target/riscv/op_helper.c

@@ -172,11 +172,15 @@ target_ulong helper_mret(CPURISCVState *env, target_ulong cpu_pc_deb)
 void helper_wfi(CPURISCVState *env)
 {
     CPUState *cs = env_cpu(env);
+    bool rvs = riscv_has_ext(env, RVS);
+    bool prv_u = env->priv == PRV_U;
+    bool prv_s = env->priv == PRV_S;
 
-    if ((env->priv == PRV_S &&
-        env->priv_ver >= PRIV_VERSION_1_10_0 &&
-        get_field(env->mstatus, MSTATUS_TW)) ||
-        riscv_cpu_virt_enabled(env)) {
+    if (((prv_s || (!rvs && prv_u)) && get_field(env->mstatus, MSTATUS_TW)) ||
+        (rvs && prv_u && !riscv_cpu_virt_enabled(env))) {
+        riscv_raise_exception(env, RISCV_EXCP_ILLEGAL_INST, GETPC());
+    } else if (riscv_cpu_virt_enabled(env) && (prv_u ||
+        (prv_s && get_field(env->hstatus, HSTATUS_VTW)))) {
         riscv_raise_exception(env, RISCV_EXCP_ILLEGAL_INST, GETPC());
     } else {
         cs->halted = 1;