target/riscv: Add a config option for ePMP

Add a config option to enable experimental support for ePMP. This
is disabled by default and can be enabled with 'x-epmp=true'.

Signed-off-by: Hongzheng-Li <Ethan.Lee.QNL@gmail.com>
Signed-off-by: Hou Weiying <weiying_hou@outlook.com>
Signed-off-by: Myriad-Dreamin <camiyoru@gmail.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Message-id: a22ccdaf9314078bc735d3b323f966623f8af020.1618812899.git.alistair.francis@wdc.com
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>

target/riscv/cpu.c

@@ -412,6 +412,14 @@ static void riscv_cpu_realize(DeviceState *dev, Error **errp)
 
     if (cpu->cfg.pmp) {
         set_feature(env, RISCV_FEATURE_PMP);
+
+        /*
+         * Enhanced PMP should only be available
+         * on harts with PMP support
+         */
+        if (cpu->cfg.epmp) {
+            set_feature(env, RISCV_FEATURE_EPMP);
+        }
     }
 
     set_resetvec(env, cpu->cfg.resetvec);
@@ -554,6 +562,8 @@ static Property riscv_cpu_properties[] = {
     DEFINE_PROP_UINT16("elen", RISCVCPU, cfg.elen, 64),
     DEFINE_PROP_BOOL("mmu", RISCVCPU, cfg.mmu, true),
     DEFINE_PROP_BOOL("pmp", RISCVCPU, cfg.pmp, true),
+    DEFINE_PROP_BOOL("x-epmp", RISCVCPU, cfg.epmp, false),
+
     DEFINE_PROP_UINT64("resetvec", RISCVCPU, cfg.resetvec, DEFAULT_RSTVEC),
     DEFINE_PROP_END_OF_LIST(),
 };

target/riscv/cpu.h

@@ -304,6 +304,7 @@ struct RISCVCPU {
         uint16_t elen;
         bool mmu;
         bool pmp;
+        bool epmp;
         uint64_t resetvec;
     } cfg;
 };