Re: xilinx-zynq-a9: cannot set up guest memory 'zynq.ext_ram'

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On 8/20/21 4:39 PM, Peter Maydell wrote:
> On Fri, 20 Aug 2021 at 15:34, David Hildenbrand <david@redhat.com> wrote:
>>
>> On 20.08.21 16:22, Bin Meng wrote:
>>> Hi Philippe,
>>>
>>> On Fri, Aug 20, 2021 at 10:10 PM Philippe Mathieu-Daudé
>>> <philmd@redhat.com> wrote:
>>>>
>>>> Hi Bin,
>>>>
>>>> On 8/20/21 4:04 PM, Bin Meng wrote:
>>>>> Hi,
>>>>>
>>>>> The following command used to work on QEMU 4.2.0, but is now broken
>>>>> with QEMU head.
>>>>>
>>>>> $ qemu-system-arm -M xilinx-zynq-a9 -display none -m 40000000
>>>>> -nographic -serial /dev/null -serial mon:stdio -monitor null -device
>>>>> loader,file=u-boot-dtb.bin,addr=0x4000000,cpu-num=0
>>>>> qemu-system-arm: cannot set up guest memory 'zynq.ext_ram': Cannot
>>>>> allocate memory
> 
>> -m 40000000
>>
>> corresponds to 38 TB if I am not wrong. Is that really what you want?
> 
> Probably not, because the zynq board's init function does:
> 
>     if (machine->ram_size > 2 * GiB) {
>         error_report("RAM size more than 2 GiB is not supported");
>         exit(EXIT_FAILURE);
>     }
> 
> It seems a bit daft that we allocate the memory before we do
> the size check. This didn't use to be this way around...
> 
> Anyway, I think the cause of this change is commit c9800965c1be6c39
> from Igor. We used to silently cap the RAM size to 2GB; now we
> complain. Or at least we would complain if we hadn't already
> tried to allocate the memory and fallen over...

Ouch... I remember having tested -M raspi2 -m 8G etc... to verify
the error messages, but didn't noticed the memory was allocated.

static void qemu_init_board(void)
{
    MachineClass *machine_class = MACHINE_GET_CLASS(current_machine);

    if (machine_class->default_ram_id && current_machine->ram_size &&
        numa_uses_legacy_mem() && !current_machine->ram_memdev_id) {
        create_default_memdev(current_machine, mem_path); // <- alloc
    }

    /* process plugin before CPUs are created ... */
    qemu_plugin_load_list(&plugin_list, &error_fatal);

    /* From here on we enter MACHINE_PHASE_INITIALIZED.  */
    machine_run_board_init(current_machine); // <- Machine::init()
                                             //    checks RAM size

    ...

$ qemu-system-x86_64 -m 1T
qemu-system-x86_64: cannot set up guest memory 'pc.ram': Cannot allocate
memory