From: Frank Chang <frank.chang@sifive.com>

Zicfilp extension introduces the MNPELP (bit 9) in mnstatus.
The MNPELP field holds the previous ELP.

When a RNMI trap is delivered, the MNPELP is set to ELP and ELP set
to NO_LP_EXPECTED. Upon a mnret, if the mnstatus.MNPP holds the
value y, then ELP is set to the value of MNPELP if yLPE is 1;
otherwise, it is set to NO_LP_EXPECTED.

Signed-off-by: Frank Chang <frank.chang@sifive.com>
Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
---
 target/riscv/cpu_bits.h   |  1 +
 target/riscv/cpu_helper.c | 11 ++++++++++-
 target/riscv/op_helper.c  |  9 +++++++++
 3 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/target/riscv/cpu_bits.h b/target/riscv/cpu_bits.h
index 17787fd693..be9d0f5c05 100644
--- a/target/riscv/cpu_bits.h
+++ b/target/riscv/cpu_bits.h
@@ -643,6 +643,7 @@ typedef enum {
 /* RNMI mnstatus CSR mask */
 #define MNSTATUS_NMIE       0x00000008
 #define MNSTATUS_MNPV       0x00000080
+#define MNSTATUS_MNPELP     0x00000200
 #define MNSTATUS_MNPP       0x00001800
 
 /* VM modes (satp.mode) privileged ISA 1.10 */
diff --git a/target/riscv/cpu_helper.c b/target/riscv/cpu_helper.c
index e5ffbbbd83..1fb1e31031 100644
--- a/target/riscv/cpu_helper.c
+++ b/target/riscv/cpu_helper.c
@@ -1918,6 +1918,10 @@ void riscv_cpu_do_interrupt(CPUState *cs)
         env->mnepc = env->pc;
         env->pc = env->rnmi_irqvec;
 
+        if (cpu_get_fcfien(env)) {
+            env->mnstatus = set_field(env->mnstatus, MNSTATUS_MNPELP, env->elp);
+        }
+
         /* Trapping to M mode, virt is disabled */
         riscv_cpu_set_mode(env, PRV_M, false);
 
@@ -2085,7 +2089,12 @@ void riscv_cpu_do_interrupt(CPUState *cs)
         /* handle the trap in M-mode */
         /* save elp status */
         if (cpu_get_fcfien(env)) {
-            env->mstatus = set_field(env->mstatus, MSTATUS_MPELP, env->elp);
+            if (nnmi_excep) {
+                env->mnstatus = set_field(env->mnstatus, MNSTATUS_MNPELP,
+                                          env->elp);
+            } else {
+                env->mstatus = set_field(env->mstatus, MSTATUS_MPELP, env->elp);
+            }
         }
 
         if (riscv_has_ext(env, RVH)) {
diff --git a/target/riscv/op_helper.c b/target/riscv/op_helper.c
index 63ec53e992..a4b625fcd9 100644
--- a/target/riscv/op_helper.c
+++ b/target/riscv/op_helper.c
@@ -402,6 +402,15 @@ target_ulong helper_mnret(CPURISCVState *env)
 
     riscv_cpu_set_mode(env, prev_priv, prev_virt);
 
+    /*
+     * If forward cfi enabled for new priv, restore elp status
+     * and clear mnpelp in mnstatus
+     */
+    if (cpu_get_fcfien(env)) {
+        env->elp = get_field(env->mnstatus, MNSTATUS_MNPELP);
+    }
+    env->mnstatus = set_field(env->mnstatus, MNSTATUS_MNPELP, 0);
+
     return retpc;
 }
 
-- 
2.34.1

On Tue, Dec 31, 2024 at 1:28 PM <frank.chang@sifive.com> wrote:
>
> From: Frank Chang <frank.chang@sifive.com>
>
> Zicfilp extension introduces the MNPELP (bit 9) in mnstatus.
> The MNPELP field holds the previous ELP.
>
> When a RNMI trap is delivered, the MNPELP is set to ELP and ELP set
> to NO_LP_EXPECTED. Upon a mnret, if the mnstatus.MNPP holds the
> value y, then ELP is set to the value of MNPELP if yLPE is 1;
> otherwise, it is set to NO_LP_EXPECTED.
>
> Signed-off-by: Frank Chang <frank.chang@sifive.com>
> Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>

Reviewed-by: Alistair Francis <alistair.francis@wdc.com>

Alistair

> ---
>  target/riscv/cpu_bits.h   |  1 +
>  target/riscv/cpu_helper.c | 11 ++++++++++-
>  target/riscv/op_helper.c  |  9 +++++++++
>  3 files changed, 20 insertions(+), 1 deletion(-)
>
> diff --git a/target/riscv/cpu_bits.h b/target/riscv/cpu_bits.h
> index 17787fd693..be9d0f5c05 100644
> --- a/target/riscv/cpu_bits.h
> +++ b/target/riscv/cpu_bits.h
> @@ -643,6 +643,7 @@ typedef enum {
>  /* RNMI mnstatus CSR mask */
>  #define MNSTATUS_NMIE       0x00000008
>  #define MNSTATUS_MNPV       0x00000080
> +#define MNSTATUS_MNPELP     0x00000200
>  #define MNSTATUS_MNPP       0x00001800
>
>  /* VM modes (satp.mode) privileged ISA 1.10 */
> diff --git a/target/riscv/cpu_helper.c b/target/riscv/cpu_helper.c
> index e5ffbbbd83..1fb1e31031 100644
> --- a/target/riscv/cpu_helper.c
> +++ b/target/riscv/cpu_helper.c
> @@ -1918,6 +1918,10 @@ void riscv_cpu_do_interrupt(CPUState *cs)
>          env->mnepc = env->pc;
>          env->pc = env->rnmi_irqvec;
>
> +        if (cpu_get_fcfien(env)) {
> +            env->mnstatus = set_field(env->mnstatus, MNSTATUS_MNPELP, env->elp);
> +        }
> +
>          /* Trapping to M mode, virt is disabled */
>          riscv_cpu_set_mode(env, PRV_M, false);
>
> @@ -2085,7 +2089,12 @@ void riscv_cpu_do_interrupt(CPUState *cs)
>          /* handle the trap in M-mode */
>          /* save elp status */
>          if (cpu_get_fcfien(env)) {
> -            env->mstatus = set_field(env->mstatus, MSTATUS_MPELP, env->elp);
> +            if (nnmi_excep) {
> +                env->mnstatus = set_field(env->mnstatus, MNSTATUS_MNPELP,
> +                                          env->elp);
> +            } else {
> +                env->mstatus = set_field(env->mstatus, MSTATUS_MPELP, env->elp);
> +            }
>          }
>
>          if (riscv_has_ext(env, RVH)) {
> diff --git a/target/riscv/op_helper.c b/target/riscv/op_helper.c
> index 63ec53e992..a4b625fcd9 100644
> --- a/target/riscv/op_helper.c
> +++ b/target/riscv/op_helper.c
> @@ -402,6 +402,15 @@ target_ulong helper_mnret(CPURISCVState *env)
>
>      riscv_cpu_set_mode(env, prev_priv, prev_virt);
>
> +    /*
> +     * If forward cfi enabled for new priv, restore elp status
> +     * and clear mnpelp in mnstatus
> +     */
> +    if (cpu_get_fcfien(env)) {
> +        env->elp = get_field(env->mnstatus, MNSTATUS_MNPELP);
> +    }
> +    env->mnstatus = set_field(env->mnstatus, MNSTATUS_MNPELP, 0);
> +
>      return retpc;
>  }
>
> --
> 2.34.1
>
>