[v4,03/16] target/riscv: save and restore elp state on priv transitions

Commit Message

Deepak Gupta Aug. 16, 2024, 1:06 a.m. UTC

elp state is recorded in *status on trap entry (less privilege to higher
privilege) and restored in elp from *status on trap exit (higher to less
privilege).

Additionally this patch introduces a forward cfi helper function to
determine if current privilege has forward cfi is enabled or not based on
*envcfg (for U, VU, S, VU, HS) or mseccfg csr (for M). For qemu-user, a
new field `ufcfien` is introduced which is by default set to false and
helper function returns value deposited in `ufcfien` for qemu-user.

Signed-off-by: Deepak Gupta <[e-mail]>
Co-developed-by: Jim Shu <[e-mail]>
Co-developed-by: Andy Chiu <[e-mail]>
---
 target/riscv/cpu.c        |  5 ++++
 target/riscv/cpu.h        |  2 ++
 target/riscv/cpu_helper.c | 55 +++++++++++++++++++++++++++++++++++++++
 target/riscv/op_helper.c  | 18 +++++++++++++
 4 files changed, 80 insertions(+)

Comments

Richard Henderson Aug. 16, 2024, 2:59 a.m. UTC | #1

On 8/16/24 11:06, Deepak Gupta wrote:
> @@ -546,6 +575,15 @@ void riscv_cpu_swap_hypervisor_regs(CPURISCVState *env)
>       }
>       bool current_virt = env->virt_enabled;
>   
> +    /*
> +     * If zicfilp extension available and henvcfg.LPE = 1,
> +     * then apply SPELP mask on mstatus
> +     */
> +    if (env_archcpu(env)->cfg.ext_zicfilp &&
> +        get_field(env->henvcfg, HENVCFG_LPE)) {
> +        mstatus_mask |= SSTATUS_SPELP;
> +    }
> +

I think this hunk belongs with the previous patch.

Otherwise.
Reviewed-by: Richard Henderson <[e-mail]>

r~

Deepak Gupta Aug. 16, 2024, 6:45 a.m. UTC | #2

On Fri, Aug 16, 2024 at 12:59:43PM +1000, Richard Henderson wrote:
>On 8/16/24 11:06, Deepak Gupta wrote:
>>@@ -546,6 +575,15 @@ void riscv_cpu_swap_hypervisor_regs(CPURISCVState *env)
>>      }
>>      bool current_virt = env->virt_enabled;
>>+    /*
>>+     * If zicfilp extension available and henvcfg.LPE = 1,
>>+     * then apply SPELP mask on mstatus
>>+     */
>>+    if (env_archcpu(env)->cfg.ext_zicfilp &&
>>+        get_field(env->henvcfg, HENVCFG_LPE)) {
>>+        mstatus_mask |= SSTATUS_SPELP;
>>+    }
>>+
>
>I think this hunk belongs with the previous patch.
>

I kept it here because this save/restore of vsstatus with effective sstatus during
VS/VU <--> HS transition. ELP also needs to get saved/restored during these transitions.

>Otherwise.
>Reviewed-by: Richard Henderson <[e-mail]>
>
>r~
>

Patch

diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
index 8e1f05e5b1..083d405516 100644
--- a/target/riscv/cpu.c
+++ b/target/riscv/cpu.c
@@ -1022,6 +1022,11 @@  static void riscv_cpu_reset_hold(Object *obj, ResetType type)
     env->load_res = -1;
     set_default_nan_mode(1, &env->fp_status);
 
+#ifdef CONFIG_USER_ONLY
+    /* qemu-user for riscv, fcfi is off by default */
+    env->ufcfien = false;
+#endif
+
 #ifndef CONFIG_USER_ONLY
     if (cpu->cfg.debug) {
         riscv_trigger_reset_hold(env);
diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h
index f966c36a31..7be0fa30f7 100644
--- a/target/riscv/cpu.h
+++ b/target/riscv/cpu.h
@@ -226,6 +226,7 @@  struct CPUArchState {
     bool      elp;
 #ifdef CONFIG_USER_ONLY
     uint32_t elf_flags;
+    bool ufcfien;
 #endif
 
 #ifndef CONFIG_USER_ONLY
@@ -530,6 +531,7 @@  void riscv_cpu_set_geilen(CPURISCVState *env, target_ulong geilen);
 bool riscv_cpu_vector_enabled(CPURISCVState *env);
 void riscv_cpu_set_virt_enabled(CPURISCVState *env, bool enable);
 int riscv_env_mmu_index(CPURISCVState *env, bool ifetch);
+bool cpu_get_fcfien(CPURISCVState *env);
 G_NORETURN void  riscv_cpu_do_unaligned_access(CPUState *cs, vaddr addr,
                                                MMUAccessType access_type,
                                                int mmu_idx, uintptr_t retaddr);
diff --git a/target/riscv/cpu_helper.c b/target/riscv/cpu_helper.c
index 6709622dd3..12484ca7d2 100644
--- a/target/riscv/cpu_helper.c
+++ b/target/riscv/cpu_helper.c
@@ -33,6 +33,7 @@ 
 #include "cpu_bits.h"
 #include "debug.h"
 #include "tcg/oversized-guest.h"
+#include "pmp.h"
 
 int riscv_env_mmu_index(CPURISCVState *env, bool ifetch)
 {
@@ -63,6 +64,34 @@  int riscv_env_mmu_index(CPURISCVState *env, bool ifetch)
 #endif
 }
 
+bool cpu_get_fcfien(CPURISCVState *env)
+{
+    /* no cfi extension, return false */
+    if (!env_archcpu(env)->cfg.ext_zicfilp) {
+        return false;
+    }
+#ifdef CONFIG_USER_ONLY
+    return env->ufcfien;
+#else
+    switch (env->priv) {
+    case PRV_U:
+        if (riscv_has_ext(env, RVS)) {
+            return env->senvcfg & MENVCFG_LPE;
+        }
+        return env->menvcfg & MENVCFG_LPE;
+    case PRV_S:
+        if (env->virt_enabled) {
+            return env->henvcfg & HENVCFG_LPE;
+        }
+        return env->menvcfg & MENVCFG_LPE;
+    case PRV_M:
+        return env->mseccfg & MSECCFG_MLPE;
+    default:
+        g_assert_not_reached();
+    }
+#endif
+}
+
 void cpu_get_tb_cpu_state(CPURISCVState *env, vaddr *pc,
                           uint64_t *cs_base, uint32_t *pflags)
 {
@@ -546,6 +575,15 @@  void riscv_cpu_swap_hypervisor_regs(CPURISCVState *env)
     }
     bool current_virt = env->virt_enabled;
 
+    /*
+     * If zicfilp extension available and henvcfg.LPE = 1,
+     * then apply SPELP mask on mstatus
+     */
+    if (env_archcpu(env)->cfg.ext_zicfilp &&
+        get_field(env->henvcfg, HENVCFG_LPE)) {
+        mstatus_mask |= SSTATUS_SPELP;
+    }
+
     g_assert(riscv_has_ext(env, RVH));
 
     if (current_virt) {
@@ -1754,6 +1792,11 @@  void riscv_cpu_do_interrupt(CPUState *cs)
     if (env->priv <= PRV_S && cause < 64 &&
         (((deleg >> cause) & 1) || s_injected || vs_injected)) {
         /* handle the trap in S-mode */
+        /* save elp status */
+        if (cpu_get_fcfien(env)) {
+            env->mstatus = set_field(env->mstatus, MSTATUS_SPELP, env->elp);
+        }
+
         if (riscv_has_ext(env, RVH)) {
             uint64_t hdeleg = async ? env->hideleg : env->hedeleg;
 
@@ -1802,6 +1845,11 @@  void riscv_cpu_do_interrupt(CPUState *cs)
         riscv_cpu_set_mode(env, PRV_S);
     } else {
         /* 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 (riscv_has_ext(env, RVH)) {
             if (env->virt_enabled) {
                 riscv_cpu_swap_hypervisor_regs(env);
@@ -1833,6 +1881,13 @@  void riscv_cpu_do_interrupt(CPUState *cs)
         riscv_cpu_set_mode(env, PRV_M);
     }
 
+    /*
+     * Interrupt/exception/trap delivery is asynchronous event and as per
+     * zicfilp spec CPU should clear up the ELP state. No harm in clearing
+     * unconditionally.
+     */
+    env->elp = false;
+
     /*
      * NOTE: it is not necessary to yield load reservations here. It is only
      * necessary for an SC from "another hart" to cause a load reservation
diff --git a/target/riscv/op_helper.c b/target/riscv/op_helper.c
index 2baf5bc3ca..5848aaf437 100644
--- a/target/riscv/op_helper.c
+++ b/target/riscv/op_helper.c
@@ -313,6 +313,15 @@  target_ulong helper_sret(CPURISCVState *env)
 
     riscv_cpu_set_mode(env, prev_priv);
 
+    /*
+     * If forward cfi enabled for new priv, restore elp status
+     * and clear spelp in mstatus
+     */
+    if (cpu_get_fcfien(env)) {
+        env->elp = get_field(env->mstatus, MSTATUS_SPELP);
+    }
+    env->mstatus = set_field(env->mstatus, MSTATUS_SPELP, 0);
+
     return retpc;
 }
 
@@ -357,6 +366,15 @@  target_ulong helper_mret(CPURISCVState *env)
         riscv_cpu_set_virt_enabled(env, prev_virt);
     }
 
+    /*
+     * If forward cfi enabled for new priv, restore elp status
+     * and clear mpelp in mstatus
+     */
+    if (cpu_get_fcfien(env)) {
+        env->elp = get_field(env->mstatus, MSTATUS_MPELP);
+    }
+    env->mstatus = set_field(env->mstatus, MSTATUS_MPELP, 0);
+
     return retpc;
 }