[RFC PATCH 2/3] target/riscv: add Ssdbltrp extension support

["Clément Léger" <cleger@rivosinc.com>]

The Ssdbltrp extension allows handling trap when being in non-reentrant
state (mainly during exception handling) for S-mode [1]. This patch add
support for this extension as an experimental extension.

Link: https://github.com/riscv/riscv-double-trap/releases/download/v0.56/riscv-double-trap.pdf [1]
Signed-off-by: Clément Léger <cleger@rivosinc.com>
---
 target/riscv/cpu.c        |  4 ++-
 target/riscv/cpu.h        |  1 +
 target/riscv/cpu_bits.h   |  7 +++++
 target/riscv/cpu_cfg.h    |  1 +
 target/riscv/cpu_helper.c | 60 ++++++++++++++++++++++++++++++++++-----
 target/riscv/csr.c        | 44 +++++++++++++++++++++-------
 target/riscv/op_helper.c  | 11 +++++++
 7 files changed, 110 insertions(+), 18 deletions(-)

diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
index 36e3e5fdaf..d159b0c6b6 100644
--- a/target/riscv/cpu.c
+++ b/target/riscv/cpu.c
@@ -182,6 +182,7 @@ const RISCVIsaExtData isa_edata_arr[] = {
     ISA_EXT_DATA_ENTRY(ssccptr, PRIV_VERSION_1_11_0, has_priv_1_11),
     ISA_EXT_DATA_ENTRY(sscofpmf, PRIV_VERSION_1_12_0, ext_sscofpmf),
     ISA_EXT_DATA_ENTRY(sscounterenw, PRIV_VERSION_1_12_0, has_priv_1_12),
+    ISA_EXT_DATA_ENTRY(ssdbltrp, PRIV_VERSION_1_12_0, ext_ssdbltrp),
     ISA_EXT_DATA_ENTRY(sstc, PRIV_VERSION_1_12_0, ext_sstc),
     ISA_EXT_DATA_ENTRY(sstvala, PRIV_VERSION_1_12_0, has_priv_1_12),
     ISA_EXT_DATA_ENTRY(sstvecd, PRIV_VERSION_1_12_0, has_priv_1_12),
@@ -276,7 +277,7 @@ static const char * const riscv_excp_names[] = {
     "load_page_fault",
     "reserved",
     "store_page_fault",
-    "reserved",
+    "double_trap",
     "reserved",
     "reserved",
     "reserved",
@@ -1572,6 +1573,7 @@ const RISCVCPUMultiExtConfig riscv_cpu_vendor_exts[] = {
 
 /* These are experimental so mark with 'x-' */
 const RISCVCPUMultiExtConfig riscv_cpu_experimental_exts[] = {
+    MULTI_EXT_CFG_BOOL("x-ssdbltrp", ext_ssdbltrp, false),
     DEFINE_PROP_END_OF_LIST(),
 };
 
diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h
index 3b1a02b944..14f83d4f05 100644
--- a/target/riscv/cpu.h
+++ b/target/riscv/cpu.h
@@ -505,6 +505,7 @@ 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 riscv_env_smode_dbltrp_enabled(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_bits.h b/target/riscv/cpu_bits.h
index 9ade72ff31..494a036f6e 100644
--- a/target/riscv/cpu_bits.h
+++ b/target/riscv/cpu_bits.h
@@ -542,6 +542,7 @@
 #define MSTATUS_TVM         0x00100000 /* since: priv-1.10 */
 #define MSTATUS_TW          0x00200000 /* since: priv-1.10 */
 #define MSTATUS_TSR         0x00400000 /* since: priv-1.10 */
+#define MSTATUS_SDT         0x01000000 /* Ssdbltrp extension */
 #define MSTATUS_GVA         0x4000000000ULL
 #define MSTATUS_MPV         0x8000000000ULL
 
@@ -572,6 +573,7 @@ typedef enum {
 #define SSTATUS_XS          0x00018000
 #define SSTATUS_SUM         0x00040000 /* since: priv-1.10 */
 #define SSTATUS_MXR         0x00080000
+#define SSTATUS_SDT         0x01000000 /* Ssdbltrp extension */
 
 #define SSTATUS64_UXL       0x0000000300000000ULL
 
@@ -670,6 +672,7 @@ 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, /* Ssdbltrp extension */
     RISCV_EXCP_SEMIHOST = 0x11,
     RISCV_EXCP_INST_GUEST_PAGE_FAULT = 0x14,
     RISCV_EXCP_LOAD_GUEST_ACCESS_FAULT = 0x15,
@@ -744,11 +747,13 @@ typedef enum RISCVException {
 #define MENVCFG_CBIE                       (3UL << 4)
 #define MENVCFG_CBCFE                      BIT(6)
 #define MENVCFG_CBZE                       BIT(7)
+#define MENVCFG_DTE                        (1ULL << 59) /* Ssdbltrp extension */
 #define MENVCFG_ADUE                       (1ULL << 61)
 #define MENVCFG_PBMTE                      (1ULL << 62)
 #define MENVCFG_STCE                       (1ULL << 63)
 
 /* For RV32 */
+#define MENVCFGH_DTE                       BIT(27) /* Ssdbltrp extension */
 #define MENVCFGH_ADUE                      BIT(29)
 #define MENVCFGH_PBMTE                     BIT(30)
 #define MENVCFGH_STCE                      BIT(31)
@@ -762,11 +767,13 @@ typedef enum RISCVException {
 #define HENVCFG_CBIE                       MENVCFG_CBIE
 #define HENVCFG_CBCFE                      MENVCFG_CBCFE
 #define HENVCFG_CBZE                       MENVCFG_CBZE
+#define HENVCFG_DTE                        MENVCFG_DTE
 #define HENVCFG_ADUE                       MENVCFG_ADUE
 #define HENVCFG_PBMTE                      MENVCFG_PBMTE
 #define HENVCFG_STCE                       MENVCFG_STCE
 
 /* For RV32 */
+#define HENVCFGH_DTE                        MENVCFGH_DTE
 #define HENVCFGH_ADUE                       MENVCFGH_ADUE
 #define HENVCFGH_PBMTE                      MENVCFGH_PBMTE
 #define HENVCFGH_STCE                       MENVCFGH_STCE
diff --git a/target/riscv/cpu_cfg.h b/target/riscv/cpu_cfg.h
index cb750154bd..a149c08167 100644
--- a/target/riscv/cpu_cfg.h
+++ b/target/riscv/cpu_cfg.h
@@ -74,6 +74,7 @@ struct RISCVCPUConfig {
     bool ext_ztso;
     bool ext_smstateen;
     bool ext_sstc;
+    bool ext_ssdbltrp;
     bool ext_svadu;
     bool ext_svinval;
     bool ext_svnapot;
diff --git a/target/riscv/cpu_helper.c b/target/riscv/cpu_helper.c
index fc090d729a..3d747e5bfc 100644
--- a/target/riscv/cpu_helper.c
+++ b/target/riscv/cpu_helper.c
@@ -62,6 +62,15 @@ int riscv_env_mmu_index(CPURISCVState *env, bool ifetch)
 #endif
 }
 
+bool riscv_env_smode_dbltrp_enabled(CPURISCVState *env)
+{
+    if (env->virt_enabled) {
+        return (env->henvcfg & HENVCFG_DTE) != 0;
+    } else {
+        return (env->menvcfg & MENVCFG_DTE) != 0;
+    }
+}
+
 void cpu_get_tb_cpu_state(CPURISCVState *env, vaddr *pc,
                           uint64_t *cs_base, uint32_t *pflags)
 {
@@ -544,7 +553,12 @@ void riscv_cpu_swap_hypervisor_regs(CPURISCVState *env)
         mstatus_mask |= MSTATUS_FS;
     }
     bool current_virt = env->virt_enabled;
+    uint64_t dte = current_virt ? env->menvcfg & MENVCFG_DTE :
+                                  env->henvcfg & HENVCFG_DTE;
 
+    if (riscv_cpu_cfg(env)->ext_ssdbltrp && dte) {
+                mstatus_mask |= MSTATUS_SDT;
+    }
     g_assert(riscv_has_ext(env, RVH));
 
     if (current_virt) {
@@ -1648,7 +1662,10 @@ void riscv_cpu_do_interrupt(CPUState *cs)
 
     RISCVCPU *cpu = RISCV_CPU(cs);
     CPURISCVState *env = &cpu->env;
+    const RISCVCPUConfig *cfg = riscv_cpu_cfg(env);
     bool write_gva = false;
+    bool smode_exception;
+    bool vsmode_exception;
     uint64_t s;
 
     /*
@@ -1662,6 +1679,8 @@ void riscv_cpu_do_interrupt(CPUState *cs)
         !(env->mip & (1 << cause));
     bool vs_injected = env->hvip & (1 << cause) & env->hvien &&
         !(env->mip & (1 << 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;
@@ -1750,14 +1769,33 @@ void riscv_cpu_do_interrupt(CPUState *cs)
                   __func__, env->mhartid, async, cause, env->pc, tval,
                   riscv_cpu_get_trap_name(cause, async));
 
-    if (env->priv <= PRV_S && cause < 64 &&
-        (((deleg >> cause) & 1) || s_injected || vs_injected)) {
-        /* handle the trap in S-mode */
+    smode_exception = env->priv <= PRV_S && cause < 64 &&
+                      (((deleg >> cause) & 1) || s_injected || vs_injected);
+    vsmode_exception = env->virt_enabled &&
+                       (((hdeleg >> cause) & 1) || vs_injected);
+    /* Check S-mode double trap condition */
+    if (cfg->ext_ssdbltrp && smode_exception) {
+        uint64_t dte = env->menvcfg & MENVCFG_DTE;
         if (riscv_has_ext(env, RVH)) {
-            uint64_t hdeleg = async ? env->hideleg : env->hedeleg;
+            if (vsmode_exception) {
+                /* Trap to VS mode, use henvcfg instead of menvcfg*/
+                dte = env->henvcfg & HENVCFG_DTE;
+            } else if (env->virt_enabled) {
+                /* Trap into HS mode, from virt
+                 * We can not have a double trap when switching from one mode to
+                 * another since sret clears the SDT flag, so when trapping in
+                 * S-mode, SDT is cleared
+                 * */
+                dte = 0;
+            }
+        }
+        smode_double_trap = dte && (env->mstatus & MSTATUS_SDT);
+    }
 
-            if (env->virt_enabled &&
-                (((hdeleg >> cause) & 1) || vs_injected)) {
+    if (smode_exception && !smode_double_trap) {
+        /* handle the trap in S-mode */
+        if (riscv_has_ext(env, RVH)) {
+            if (vsmode_exception) {
                 /* Trap to VS mode */
                 /*
                  * See if we need to adjust cause. Yes if its VS mode interrupt
@@ -1790,6 +1828,9 @@ 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)) {
+            s = set_field(s, MSTATUS_SDT, 1);
+        }
         env->mstatus = s;
         env->scause = cause | ((target_ulong)async << (TARGET_LONG_BITS - 1));
         env->sepc = env->pc;
@@ -1823,9 +1864,14 @@ void riscv_cpu_do_interrupt(CPUState *cs)
         s = set_field(s, MSTATUS_MIE, 0);
         env->mstatus = s;
         env->mcause = cause | ~(((target_ulong)-1) >> async);
+        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;
         env->pc = (env->mtvec >> 2 << 2) +
                   ((async && (env->mtvec & 3) == 1) ? cause * 4 : 0);
diff --git a/target/riscv/csr.c b/target/riscv/csr.c
index 726096444f..1a2e739947 100644
--- a/target/riscv/csr.c
+++ b/target/riscv/csr.c
@@ -514,6 +514,15 @@ static RISCVException aia_hmode32(CPURISCVState *env, int csrno)
     return hmode32(env, csrno);
 }
 
+static RISCVException dbltrp_hmode(CPURISCVState *env, int csrno)
+{
+    if (riscv_cpu_cfg(env)->ext_ssdbltrp) {
+        return RISCV_EXCP_NONE;
+    }
+
+    return hmode(env, csrno);
+}
+
 static RISCVException pmp(CPURISCVState *env, int csrno)
 {
     if (riscv_cpu_cfg(env)->pmp) {
@@ -1182,7 +1191,7 @@ static const target_ulong vs_delegable_excps = DELEGABLE_EXCPS &
       (1ULL << (RISCV_EXCP_STORE_GUEST_AMO_ACCESS_FAULT)));
 static const target_ulong sstatus_v1_10_mask = SSTATUS_SIE | SSTATUS_SPIE |
     SSTATUS_UIE | SSTATUS_UPIE | SSTATUS_SPP | SSTATUS_FS | SSTATUS_XS |
-    SSTATUS_SUM | SSTATUS_MXR | SSTATUS_VS;
+    SSTATUS_SUM | SSTATUS_MXR | SSTATUS_VS | SSTATUS_SDT;
 
 /*
  * Spec allows for bits 13:63 to be either read-only or writable.
@@ -1380,6 +1389,13 @@ static RISCVException write_mstatus(CPURISCVState *env, int csrno,
         mask |= MSTATUS_VS;
     }
 
+    if (riscv_env_smode_dbltrp_enabled(env)) {
+        mask |= MSTATUS_SDT;
+        if ((val & MSTATUS_SDT) != 0) {
+            mask &= ~MSTATUS_SIE;
+        }
+    }
+
     if (xl != MXL_RV32 || env->debugger) {
         if (riscv_has_ext(env, RVH)) {
             mask |= MSTATUS_MPV | MSTATUS_GVA;
@@ -2089,7 +2105,8 @@ static RISCVException write_menvcfg(CPURISCVState *env, int csrno,
     if (riscv_cpu_mxl(env) == MXL_RV64) {
         mask |= (cfg->ext_svpbmt ? MENVCFG_PBMTE : 0) |
                 (cfg->ext_sstc ? MENVCFG_STCE : 0) |
-                (cfg->ext_svadu ? MENVCFG_ADUE : 0);
+                (cfg->ext_svadu ? MENVCFG_ADUE : 0) |
+                (cfg->ext_ssdbltrp ? MENVCFG_DTE : 0);
     }
     env->menvcfg = (env->menvcfg & ~mask) | (val & mask);
 
@@ -2109,7 +2126,8 @@ static RISCVException write_menvcfgh(CPURISCVState *env, int csrno,
     const RISCVCPUConfig *cfg = riscv_cpu_cfg(env);
     uint64_t mask = (cfg->ext_svpbmt ? MENVCFG_PBMTE : 0) |
                     (cfg->ext_sstc ? MENVCFG_STCE : 0) |
-                    (cfg->ext_svadu ? MENVCFG_ADUE : 0);
+                    (cfg->ext_svadu ? MENVCFG_ADUE : 0) |
+                    (cfg->ext_ssdbltrp ? MENVCFG_DTE : 0);
     uint64_t valh = (uint64_t)val << 32;
 
     env->menvcfg = (env->menvcfg & ~mask) | (valh & mask);
@@ -2160,9 +2178,10 @@ static RISCVException read_henvcfg(CPURISCVState *env, int csrno,
      * henvcfg.pbmte is read_only 0 when menvcfg.pbmte = 0
      * henvcfg.stce is read_only 0 when menvcfg.stce = 0
      * henvcfg.adue is read_only 0 when menvcfg.adue = 0
+     * henvcfg.dte is read_only 0 when menvcfg.dte = 0
      */
-    *val = env->henvcfg & (~(HENVCFG_PBMTE | HENVCFG_STCE | HENVCFG_ADUE) |
-                           env->menvcfg);
+    *val = env->henvcfg & (~(HENVCFG_PBMTE | HENVCFG_STCE | HENVCFG_ADUE |
+                             HENVCFG_DTE) | env->menvcfg);
     return RISCV_EXCP_NONE;
 }
 
@@ -2170,6 +2189,7 @@ static RISCVException write_henvcfg(CPURISCVState *env, int csrno,
                                     target_ulong val)
 {
     uint64_t mask = HENVCFG_FIOM | HENVCFG_CBIE | HENVCFG_CBCFE | HENVCFG_CBZE;
+    uint64_t menvcfg_mask;
     RISCVException ret;
 
     ret = smstateen_acc_ok(env, 0, SMSTATEEN0_HSENVCFG);
@@ -2178,7 +2198,11 @@ static RISCVException write_henvcfg(CPURISCVState *env, int csrno,
     }
 
     if (riscv_cpu_mxl(env) == MXL_RV64) {
-        mask |= env->menvcfg & (HENVCFG_PBMTE | HENVCFG_STCE | HENVCFG_ADUE);
+        menvcfg_mask = HENVCFG_PBMTE | HENVCFG_STCE | HENVCFG_ADUE;
+        if (riscv_cpu_cfg(env)->ext_ssdbltrp) {
+            menvcfg_mask |= HENVCFG_DTE;
+        }
+        mask |= env->menvcfg & menvcfg_mask;
     }
 
     env->henvcfg = (env->henvcfg & ~mask) | (val & mask);
@@ -2196,8 +2220,8 @@ static RISCVException read_henvcfgh(CPURISCVState *env, int csrno,
         return ret;
     }
 
-    *val = (env->henvcfg & (~(HENVCFG_PBMTE | HENVCFG_STCE | HENVCFG_ADUE) |
-                            env->menvcfg)) >> 32;
+    *val = (env->henvcfg & (~(HENVCFG_PBMTE | HENVCFG_STCE | HENVCFG_ADUE |
+                              HENVCFG_DTE) | env->menvcfg)) >> 32;
     return RISCV_EXCP_NONE;
 }
 
@@ -2205,7 +2229,7 @@ static RISCVException write_henvcfgh(CPURISCVState *env, int csrno,
                                      target_ulong val)
 {
     uint64_t mask = env->menvcfg & (HENVCFG_PBMTE | HENVCFG_STCE |
-                                    HENVCFG_ADUE);
+                                    HENVCFG_ADUE | HENVCFG_DTE);
     uint64_t valh = (uint64_t)val << 32;
     RISCVException ret;
 
@@ -4801,7 +4825,7 @@ riscv_csr_operations csr_ops[CSR_TABLE_SIZE] = {
     [CSR_VSATP]       = { "vsatp",       hmode,   read_vsatp,    write_vsatp,
                           .min_priv_ver = PRIV_VERSION_1_12_0                },
 
-    [CSR_MTVAL2]      = { "mtval2",      hmode,   read_mtval2,   write_mtval2,
+    [CSR_MTVAL2]      = { "mtval2",      dbltrp_hmode,   read_mtval2,   write_mtval2,
                           .min_priv_ver = PRIV_VERSION_1_12_0                },
     [CSR_MTINST]      = { "mtinst",      hmode,   read_mtinst,   write_mtinst,
                           .min_priv_ver = PRIV_VERSION_1_12_0                },
diff --git a/target/riscv/op_helper.c b/target/riscv/op_helper.c
index f414aaebdb..468ee58a00 100644
--- a/target/riscv/op_helper.c
+++ b/target/riscv/op_helper.c
@@ -289,6 +289,17 @@ target_ulong helper_sret(CPURISCVState *env)
                         get_field(mstatus, MSTATUS_SPIE));
     mstatus = set_field(mstatus, MSTATUS_SPIE, 1);
     mstatus = set_field(mstatus, MSTATUS_SPP, PRV_U);
+    if (riscv_cpu_cfg(env)->ext_ssdbltrp) {
+        if (env->virt_enabled) {
+            if (get_field(env->henvcfg, HENVCFG_DTE)) {
+                mstatus = set_field(mstatus, MSTATUS_SDT, 0);
+            }
+        } else {
+            if (get_field(env->menvcfg, MENVCFG_DTE)) {
+                mstatus = set_field(mstatus, MSTATUS_SDT, 0);
+            }
+        }
+    }
     if (env->priv_ver >= PRIV_VERSION_1_12_0) {
         mstatus = set_field(mstatus, MSTATUS_MPRV, 0);
     }
-- 
2.43.0