A code error in accel/tcg/user-exec.c
Description of problem:
accel/tcg/user-exec.c:
```
static int probe_access_internal(CPUArchState *env, vaddr addr,
                                 int fault_size, MMUAccessType access_type,
                                 bool nonfault, uintptr_t ra)
{
    int acc_flag;
    bool maperr;

    switch (access_type) {
    case MMU_DATA_STORE:
        acc_flag = PAGE_WRITE_ORG;
        break;
    case MMU_DATA_LOAD:
        acc_flag = PAGE_READ;
        break;
    case MMU_INST_FETCH:
        acc_flag = PAGE_EXEC;
        break;
    default:
        g_assert_not_reached();
    }

    if (guest_addr_valid_untagged(addr)) {
        int page_flags = page_get_flags(addr);
        if (page_flags & acc_flag) {
            if ((acc_flag == PAGE_READ || acc_flag == PAGE_WRITE)
                && cpu_plugin_mem_cbs_enabled(env_cpu(env))) {
                return TLB_MMIO;
            }
            return 0; /* success */
        }
        maperr = !(page_flags & PAGE_VALID);
    } else {
        maperr = true;
    }

    if (nonfault) {
        return TLB_INVALID_MASK;
    }

    cpu_loop_exit_sigsegv(env_cpu(env), addr, access_type, maperr, ra);
}
```
The conditional judgment "acc_flag == PAGE_WRITE" seems to have an issue, because acc_flag can only be PAGE_WRITE_ORG, PAGE_READ or PAGE_EXEC from the previous code.