Re: [PATCH for-7.1] hw/mips/malta: turn off x86 specific features of PIIX4_PM

[Igor Mammedov <imammedo@redhat.com>]

On Thu, 28 Jul 2022 16:04:58 +0100
Peter Maydell <peter.maydell@linaro.org> wrote:

> On Thu, 28 Jul 2022 at 15:44, Dr. David Alan Gilbert
> <dgilbert@redhat.com> wrote:
> >
> > * Igor Mammedov (imammedo@redhat.com) wrote:  
> > > QEMU crashes trying to save VMSTATE when only MIPS target are compiled in
> > >   $ qemu-system-mips -monitor stdio
> > >   (qemu) migrate "exec:gzip -c > STATEFILE.gz"
> > >   Segmentation fault (core dumped)
> > >
> > > It happens due to PIIX4_PM trying to parse hotplug vmstate structures
> > > which are valid only for x86 and not for MIPS (as it requires ACPI
> > > tables support which is not existent for ithe later)
> > >
> > > Issue was probably exposed by trying to cleanup/compile out unused
> > > ACPI bits from MIPS target (but forgetting about migration bits).
> > >
> > > Disable compiled out features using compat properties as the least
> > > risky way to deal with issue.  
> >
> > Isn't the problem partially due to a 'stub' vmsd which isn't terminated?  
> 
> Yes, but setting these properties causes that vmsd
> (vmstate_acpi_pcihp_pci_status) to not be used:
> 
>  * it is used only in VMSTATE_PCI_HOTPLUG()
>  * that macro is used only in hw/acpi/ich9.c (not relevant here) and
>    hw/acpi/piix4.c
>  * in piix4.c it is invoked passing it the test functions
>    vmstate_test_use_acpi_hotplug_bridge and
>    vmstate_test_migrate_acpi_index
>  * setting the properties on the device as this patch does
>    causes those test functions to return false, so the
>    vmstate_acpi_pcihp_pci_status is never examined

it's not limited to VMSTATE_PCI_HOTPLUG but also memory hotplug
and other x86 specific knobs that may cause crash.
(I ignored cpu hotplug one for now since it doesn't cause crash)

> 
> -- PMM
>