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

[Bernhard Beschow <shentey@gmail.com>]

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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?

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

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