[PULL 42/50] target/riscv: Implement Ssdbltrp exception handling

[Alistair Francis]

From: Clément Léger <cleger@rivosinc.com>

When the Ssdbltrp ISA extension is enabled, if a trap happens in S-mode
while SSTATUS.SDT isn't cleared, generate a double trap exception to
M-mode.

Signed-off-by: Clément Léger <cleger@rivosinc.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20250110125441.3208676-5-cleger@rivosinc.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
---
 target/riscv/cpu_bits.h   |  1 +
 target/riscv/cpu.c        |  2 +-
 target/riscv/cpu_helper.c | 42 ++++++++++++++++++++++++++++++++++-----
 3 files changed, 39 insertions(+), 6 deletions(-)

diff --git a/target/riscv/cpu_bits.h b/target/riscv/cpu_bits.h
index 0a56163d73..a3acda4bc8 100644
--- a/target/riscv/cpu_bits.h
+++ b/target/riscv/cpu_bits.h
@@ -701,6 +701,7 @@ typedef enum RISCVException {
     RISCV_EXCP_INST_PAGE_FAULT = 0xc, /* since: priv-1.10.0 */
     RISCV_EXCP_LOAD_PAGE_FAULT = 0xd, /* since: priv-1.10.0 */
     RISCV_EXCP_STORE_PAGE_FAULT = 0xf, /* since: priv-1.10.0 */
+    RISCV_EXCP_DOUBLE_TRAP = 0x10,
     RISCV_EXCP_SW_CHECK = 0x12, /* since: priv-1.13.0 */
     RISCV_EXCP_HW_ERR = 0x13, /* since: priv-1.13.0 */
     RISCV_EXCP_INST_GUEST_PAGE_FAULT = 0x14,
diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
index fe470f646d..5540eb7f63 100644
--- a/target/riscv/cpu.c
+++ b/target/riscv/cpu.c
@@ -303,7 +303,7 @@ static const char * const riscv_excp_names[] = {
     "load_page_fault",
     "reserved",
     "store_page_fault",
-    "reserved",
+    "double_trap",
     "reserved",
     "reserved",
     "reserved",
diff --git a/target/riscv/cpu_helper.c b/target/riscv/cpu_helper.c
index 1eac0a0062..539ba327e7 100644
--- a/target/riscv/cpu_helper.c
+++ b/target/riscv/cpu_helper.c
@@ -1951,6 +1951,7 @@ void riscv_cpu_do_interrupt(CPUState *cs)
     bool virt = env->virt_enabled;
     bool write_gva = false;
     bool always_storeamo = (env->excp_uw2 & RISCV_UW2_ALWAYS_STORE_AMO);
+    bool vsmode_exc;
     uint64_t s;
     int mode;
 
@@ -1965,6 +1966,8 @@ void riscv_cpu_do_interrupt(CPUState *cs)
         !(env->mip & (1ULL << cause));
     bool vs_injected = env->hvip & (1ULL << cause) & env->hvien &&
         !(env->mip & (1ULL << cause));
+    bool smode_double_trap = false;
+    uint64_t hdeleg = async ? env->hideleg : env->hedeleg;
     target_ulong tval = 0;
     target_ulong tinst = 0;
     target_ulong htval = 0;
@@ -2088,6 +2091,30 @@ void riscv_cpu_do_interrupt(CPUState *cs)
     mode = env->priv <= PRV_S && cause < 64 &&
         (((deleg >> cause) & 1) || s_injected || vs_injected) ? PRV_S : PRV_M;
 
+    vsmode_exc = env->virt_enabled && (((hdeleg >> cause) & 1) || vs_injected);
+    /*
+     * Check double trap condition only if already in S-mode and targeting
+     * S-mode
+     */
+    if (cpu->cfg.ext_ssdbltrp && env->priv == PRV_S && mode == PRV_S) {
+        bool dte = (env->menvcfg & MENVCFG_DTE) != 0;
+        bool sdt = (env->mstatus & MSTATUS_SDT) != 0;
+        /* In VS or HS */
+        if (riscv_has_ext(env, RVH)) {
+            if (vsmode_exc) {
+                /* VS -> VS, use henvcfg instead of menvcfg*/
+                dte = (env->henvcfg & HENVCFG_DTE) != 0;
+            } else if (env->virt_enabled) {
+                /* VS -> HS, use mstatus_hs */
+                sdt = (env->mstatus_hs & MSTATUS_SDT) != 0;
+            }
+        }
+        smode_double_trap = dte && sdt;
+        if (smode_double_trap) {
+            mode = PRV_M;
+        }
+    }
+
     if (mode == PRV_S) {
         /* handle the trap in S-mode */
         /* save elp status */
@@ -2096,10 +2123,7 @@ void riscv_cpu_do_interrupt(CPUState *cs)
         }
 
         if (riscv_has_ext(env, RVH)) {
-            uint64_t hdeleg = async ? env->hideleg : env->hedeleg;
-
-            if (env->virt_enabled &&
-                (((hdeleg >> cause) & 1) || vs_injected)) {
+            if (vsmode_exc) {
                 /* Trap to VS mode */
                 /*
                  * See if we need to adjust cause. Yes if its VS mode interrupt
@@ -2132,6 +2156,9 @@ void riscv_cpu_do_interrupt(CPUState *cs)
         s = set_field(s, MSTATUS_SPIE, get_field(s, MSTATUS_SIE));
         s = set_field(s, MSTATUS_SPP, env->priv);
         s = set_field(s, MSTATUS_SIE, 0);
+        if (riscv_env_smode_dbltrp_enabled(env, virt)) {
+            s = set_field(s, MSTATUS_SDT, 1);
+        }
         env->mstatus = s;
         sxlen = 16 << riscv_cpu_sxl(env);
         env->scause = cause | ((target_ulong)async << (sxlen - 1));
@@ -2184,9 +2211,14 @@ void riscv_cpu_do_interrupt(CPUState *cs)
         s = set_field(s, MSTATUS_MIE, 0);
         env->mstatus = s;
         env->mcause = cause | ((target_ulong)async << (mxlen - 1));
+        if (smode_double_trap) {
+            env->mtval2 = env->mcause;
+            env->mcause = RISCV_EXCP_DOUBLE_TRAP;
+        } else {
+            env->mtval2 = mtval2;
+        }
         env->mepc = env->pc;
         env->mtval = tval;
-        env->mtval2 = mtval2;
         env->mtinst = tinst;
 
         /*
-- 
2.47.1