Re: [PATCH v2 10/18] target/riscv: Implement WorldGuard CSRs

[Daniel Henrique Barboza]

On 4/17/25 7:52 AM, Jim Shu wrote:

The WG v0.4 specification adds 3 CSRs to configure S/U/HS/VS-mode WIDs
of CPUs in the higher privileged modes.

The Smwg extension at least requires a RISC-V HART to have M/U-mode, and
the Sswg/Smwgd extension at least requires a RISC-V HART to have
M/S/U-mode.

Signed-off-by: Jim Shu <jim....@sifive.com>
---

Reviewed-by: Daniel Henrique Barboza <dbarb...@ventanamicro.com>

  target/riscv/cpu.c |   4 ++
  target/riscv/cpu.h |   5 +++
  target/riscv/csr.c | 107 +++++++++++++++++++++++++++++++++++++++++++++
  3 files changed, 116 insertions(+)

diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
index a182e8c61f..1dbeac0509 100644
--- a/target/riscv/cpu.c
+++ b/target/riscv/cpu.c
@@ -1141,6 +1141,10 @@ static void riscv_cpu_reset_hold(Object *obj, ResetType 
type)
          env->mnstatus = set_field(env->mnstatus, MNSTATUS_NMIE, false);
      }

+ if (riscv_cpu_cfg(env)->ext_smwg && env->wg_reset) {

+        env->wg_reset(env);
+    }
+
      if (kvm_enabled()) {
          kvm_riscv_reset_vcpu(cpu);
      }
diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h
index 6dfc260a07..7bffe62f70 100644
--- a/target/riscv/cpu.h
+++ b/target/riscv/cpu.h
@@ -501,6 +501,11 @@ struct CPUArchState {
      uint64_t rnmi_irqvec;
      uint64_t rnmi_excpvec;

+ /* RISC-V WorldGuard */

+    target_ulong mlwid;
+    target_ulong slwid;
+    target_ulong mwiddeleg;
+
      /* machine specific WorldGuard callback */
      void (*wg_reset)(CPURISCVState *env);
      void (*wid_to_mem_attrs)(MemTxAttrs *attrs, uint32_t wid);
diff --git a/target/riscv/csr.c b/target/riscv/csr.c
index 7948188356..614df37d00 100644
--- a/target/riscv/csr.c
+++ b/target/riscv/csr.c
@@ -5388,6 +5388,109 @@ static int write_mnstatus(CPURISCVState *env, int 
csrno, target_ulong val)
      return RISCV_EXCP_NONE;
  }

+/* RISC-V Worldguard */

+static RISCVException worldguard_umode(CPURISCVState *env, int csrno)
+{
+    if (!riscv_cpu_cfg(env)->ext_smwg) {
+        return RISCV_EXCP_ILLEGAL_INST;
+    }
+
+    return umode(env, csrno);
+}
+
+static RISCVException worldguard_sumode(CPURISCVState *env, int csrno)
+{
+    RISCVException ret;
+
+    if (!riscv_cpu_cfg(env)->ext_sswg) {
+        return RISCV_EXCP_ILLEGAL_INST;
+    }
+
+    ret = smode(env, csrno);
+
+    if (ret != RISCV_EXCP_NONE) {
+        return ret;
+    }
+
+    return umode(env, csrno);
+}
+
+static RISCVException rmw_mlwid(CPURISCVState *env, int csrno,
+                                target_ulong *ret_val,
+                                target_ulong new_val, target_ulong wr_mask)
+{
+    CPUState *cs = env_cpu(env);
+    RISCVCPU *cpu = RISCV_CPU(cs);
+    target_ulong new_mlwid = (env->mlwid & ~wr_mask) | (new_val & wr_mask);
+
+    if (ret_val) {
+        *ret_val = env->mlwid;
+    }
+
+    g_assert(cpu->cfg.mwidlist);
+    if (!(BIT(new_mlwid) & cpu->cfg.mwidlist)) {
+        /* Set WID to lowest legal value if writing illegal value (WARL) */
+        new_mlwid = find_first_bit((unsigned long *)&cpu->cfg.mwidlist, 32);
+    }
+
+    if (env->mlwid != new_mlwid) {
+        env->mlwid = new_mlwid;
+        tlb_flush(cs);
+    }
+
+    return RISCV_EXCP_NONE;
+}
+
+static RISCVException rmw_slwid(CPURISCVState *env, int csrno,
+                                target_ulong *ret_val,
+                                target_ulong new_val, target_ulong wr_mask)
+{
+    target_ulong new_slwid = (env->slwid & ~wr_mask) | (new_val & wr_mask);
+
+    if (!env->mwiddeleg) {
+        /*
+         * When mwiddeleg CSR is zero, access to slwid raises an illegal
+         * instruction exception.
+         */
+        return RISCV_EXCP_ILLEGAL_INST;
+    }
+
+    if (ret_val) {
+        *ret_val = env->slwid;
+    }
+
+    if (!(BIT(new_slwid) & env->mwiddeleg)) {
+        /* Set WID to lowest legal value if writing illegal value (WARL) */
+        new_slwid = find_first_bit(
+            (unsigned long *)&env->mwiddeleg, TARGET_LONG_BITS);
+    }
+
+    if (env->slwid != new_slwid) {
+        env->slwid = new_slwid;
+        tlb_flush(env_cpu(env));
+    }
+
+    return RISCV_EXCP_NONE;
+}
+
+static RISCVException rmw_mwiddeleg(CPURISCVState *env, int csrno,
+                                    target_ulong *ret_val,
+                                    target_ulong new_val, target_ulong wr_mask)
+{
+    CPUState *cs = env_cpu(env);
+    RISCVCPU *cpu = RISCV_CPU(cs);
+
+    if (ret_val) {
+        *ret_val = env->mwiddeleg;
+    }
+
+    env->mwiddeleg = (env->mwiddeleg & ~wr_mask) | (new_val & wr_mask);
+
+    /* Core wgMarker can only have WID value in mwidlist. */
+    env->mwiddeleg &= cpu->cfg.mwidlist;
+
+    return RISCV_EXCP_NONE;
+}
  #endif

/* Crypto Extension */

@@ -6465,5 +6568,9 @@ riscv_csr_operations csr_ops[CSR_TABLE_SIZE] = {
      [CSR_SCOUNTOVF]      = { "scountovf", sscofpmf,  read_scountovf,
                               .min_priv_ver = PRIV_VERSION_1_12_0 },

+ /* RISC-V WorldGuard */

+    [CSR_MLWID]     = { "mlwid",     worldguard_umode,  NULL, NULL, rmw_mlwid 
},
+    [CSR_SLWID]     = { "slwid",     worldguard_sumode, NULL, NULL, rmw_slwid 
},
+    [CSR_MWIDDELEG] = { "mwiddeleg", worldguard_sumode, NULL, NULL, 
rmw_mwiddeleg },
  #endif /* !CONFIG_USER_ONLY */
  };