Re: [PATCH v3 8/9] hw/i386/x86: Make TYPE_X86_MACHINE the owner of smram

[Juan Quintela]

Bernhard Beschow <shentey@gmail.com> wrote:
v> On Mon, Feb 6, 2023 at 11:06 AM Juan Quintela <quintela@redhat.com> wrote:
>
>> Philippe Mathieu-Daudé <philmd@linaro.org> wrote:
>> > On 4/2/23 16:10, Bernhard Beschow wrote:
>> >> Treat the smram MemoryRegion analoguous to other memory regions such as
>> >> ram, pci, io, ... , making the used memory regions more explicit when
>> >> instantiating q35 or i440fx.
>> >> Note that the q35 device uses these memory regions only during the
>> >> realize phase which suggests that it shouldn't be the owner of smram.
>> >
>> > Few years ago I tried something similar and it wasn't accepted because
>> > the MR owner name is used in the migration stream, so this was breaking
>> > migrating from older machines.
>>
>> I don't remember the details O:-)
>>
>> Migration code, really depends on RAMBlocks names, not memory region
>> names.  But as far as I remember, that don't matter too much because the
>> memory region names ends tangled quite a bit with the RAMBlock name, right?
>>
>> > Adding David/Juan for double-checking that.
>>
>>     trace_vmstate_save(se->idstr, se->vmsd ? se->vmsd->name : "(old)");
>>
>> You can try to enable this trace and see that every section has the same
>> name with and without your change (i.e. that memory region name is not
>> seen by the migration stream).
>>
>> But that is the only help that I can came with.
>>
>> The code that you are changing (smram) is something that I don't know
>> about to give you more help.
>>
>> Looking at the patch, it looks that the name was before and now the
>> "sram", so perhaps it could help.  But I don't know.
>>
>> In the i440fx you say that you only use it until realize, so you should
>> be safe.
>>
>> For q35, it is not clear to me.
>>
>> If the trace don't show new names, I will just try:
>> - migrate a i440fx machine from binary without your patch to one with
>>   your patch
>> - the same for q35.
>>
>> And depending on the result, we can go from there.
>>
>
> Thanks for the pointers, Juan!
>
> I took some inspiration and created four migration files,
> {pc,q35}-{before,after}.mig by running `qemu-system-x86_64 -M {pc,q35} -S`
> with qemu built from master and from my branch. Then I basically ran
>  `./scripts/analyze-migration.py -d desc -f *.mig > *.json` on the four
> files and compared the diffs. Both diffs were empty. AFAIU this proves that
> there is no binary change, right?

We have two options here:
- you are right (my opinion)
- you got a bug in analyze-migration.py script and you have a new job.

But I think you can send this patch.

Later, Juan.

> Best regards,
> Bernhard
>>
>>
>> Later, Juan.
>>
>>