target/riscv: Use a smaller guess size for no-MMU PMP

Signed-off-by: NAlistair Francis <alistair.francis@wdc.com>
Reviewed-by: NBin Meng <bin.meng@windriver.com>

target/riscv/pmp.c

@@ -233,12 +233,16 @@ bool pmp_hart_has_privs(CPURISCVState *env, target_ulong addr,
         return true;
     }
 
-    /*
-     * if size is unknown (0), assume that all bytes
-     * from addr to the end of the page will be accessed.
-     */
     if (size == 0) {
-        pmp_size = -(addr | TARGET_PAGE_MASK);
+        if (riscv_feature(env, RISCV_FEATURE_MMU)) {
+            /*
+             * If size is unknown (0), assume that all bytes
+             * from addr to the end of the page will be accessed.
+             */
+            pmp_size = -(addr | TARGET_PAGE_MASK);
+        } else {
+            pmp_size = sizeof(target_ulong);
+        }
     } else {
         pmp_size = size;
     }