target/riscv: Add Smdbltrp ISA extension enable switch

Add the switch to enable the Smdbltrp ISA extension and disable it for
the max cpu. Indeed, OpenSBI when Smdbltrp is present, M-mode double
trap is enabled by default and MSTATUS.MDT needs to be cleared to avoid
taking a double trap. OpenSBI does not currently support it so disable
it for the max cpu to avoid breaking regression tests.

Signed-off-by: Clément Léger <cleger@rivosinc.com>
Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Message-ID: <20250116131539.2475785-1-cleger@rivosinc.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

Author: clementleger

target/riscv/cpu.c

@@ -194,6 +194,7 @@ const RISCVIsaExtData isa_edata_arr[] = {
     ISA_EXT_DATA_ENTRY(smcdeleg, PRIV_VERSION_1_13_0, ext_smcdeleg),
     ISA_EXT_DATA_ENTRY(smcntrpmf, PRIV_VERSION_1_12_0, ext_smcntrpmf),
     ISA_EXT_DATA_ENTRY(smcsrind, PRIV_VERSION_1_13_0, ext_smcsrind),
+    ISA_EXT_DATA_ENTRY(smdbltrp, PRIV_VERSION_1_13_0, ext_smdbltrp),
     ISA_EXT_DATA_ENTRY(smepmp, PRIV_VERSION_1_12_0, ext_smepmp),
     ISA_EXT_DATA_ENTRY(smrnmi, PRIV_VERSION_1_12_0, ext_smrnmi),
     ISA_EXT_DATA_ENTRY(smmpm, PRIV_VERSION_1_13_0, ext_smmpm),
@@ -1626,6 +1627,7 @@ const RISCVCPUMultiExtConfig riscv_cpu_extensions[] = {
     MULTI_EXT_CFG_BOOL("ssnpm", ext_ssnpm, false),
 
     MULTI_EXT_CFG_BOOL("smaia", ext_smaia, false),
+    MULTI_EXT_CFG_BOOL("smdbltrp", ext_smdbltrp, false),
     MULTI_EXT_CFG_BOOL("smepmp", ext_smepmp, false),
     MULTI_EXT_CFG_BOOL("smrnmi", ext_smrnmi, false),
     MULTI_EXT_CFG_BOOL("smmpm", ext_smmpm, false),

target/riscv/tcg/tcg-cpu.c

@@ -1439,6 +1439,16 @@ static void riscv_init_max_cpu_extensions(Object *obj)
         isa_ext_update_enabled(cpu, CPU_CFG_OFFSET(ext_smrnmi), false);
         qemu_log("Smrnmi is disabled in the 'max' type CPU\n");
     }
+
+    /*
+     * ext_smdbltrp requires the firmware to clear MSTATUS.MDT on startup to
+     * avoid generating a double trap. OpenSBI does not currently support it,
+     * disable it for now.
+     */
+    if (cpu->cfg.ext_smdbltrp) {
+        isa_ext_update_enabled(cpu, CPU_CFG_OFFSET(ext_smdbltrp), false);
+        qemu_log("Smdbltrp is disabled in the 'max' type CPU\n");
+    }
 }
 
 static bool riscv_cpu_has_max_extensions(Object *cpu_obj)